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2016 | Buch

New Results in Numerical and Experimental Fluid Mechanics X

Contributions to the 19th STAB/DGLR Symposium Munich, Germany, 2014

herausgegeben von: Andreas Dillmann, Gerd Heller, Ewald Krämer, Claus Wagner, Christian Breitsamter

Verlag: Springer International Publishing

Buchreihe : Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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SUCHEN

Über dieses Buch

This book presents contributions to the 19th biannual symposium of the German Aerospace Aerodynamics Association (STAB) and the German Society for Aeronautics and Astronautics (DGLR). The individual chapters reflect ongoing research conducted by the STAB members in the field of numerical and experimental fluid mechanics and aerodynamics, mainly for (but not limited to) aerospace applications, and cover both nationally and EC-funded projects. Special emphasis is given to collaborative research projects conducted by German scientists and engineers from universities, research-establishments and industries. By addressing a number of cutting-edge applications, together with the relevant physical and mathematics fundamentals, the book provides readers with a comprehensive overview of the current research work in the field. Though the book’s primary emphasis is on the aerospace context, it also addresses further important applications, e.g. in ground transportation and energy.

Inhaltsverzeichnis

Frontmatter

Airplane Aerodynamics/Propulsion Integration

Frontmatter
Numerical Stall Behavior Investigation of an Aircraft Equipped with Coanda Flap and Droop Nose

An active high-lift set up is employed on a wing-body aircraft configuration and the stall behavior is analyzed by means of CFD RANS simulations. The high-lift system is composed of a trailing-edge gap-less Coanda flap and a leading-edge flexible droop nose. The effect of the leading-edge device is studied by using comparisons with the cruise leading-edge configuration. Comparisons with previous 2D simulations highlight lower lift performances for the wing section of the 3D model with respect to the airfoil data. This is due to 3D flow dynamics that limit the lift generated by the wing and induce stall with mechanisms not observed in 2D. Cross flow at the wing leading edge, or over the suction side of the wing root, increase the boundary layer thickness over the wing, thus reducing the efficiency of the Coanda flap.

Marco Burnazzi, Jakob Thiemeier, Rolf Radespiel
Aerodynamic Design of a Folded Krüger Device for a HLFC Wing

This work presents the design of a folded Krüger device under realistic geometrical requirements for a wing with hybrid laminar flow control (HLFC). A focus is laid on the investigation of the trade-off between space allocation of the retracted Krüger and the aerodynamic high-lift performance. The results reveal that the Krüger device is able to replace a reference slat device in relation to its aerodynamic high-lift performance. Further on the reduction of the allocation space influences the high-lift performance unfavorably.

Dirk M. Franke, Jochen Wild
Validation of CFD Airdrop Simulations in the Vortical Wake of an Aircraft with Open Ramp

During the first few seconds of an airdrop the supplies heavily interact with the wake of the military transport aircraft. Due to the particular shape of their rear fuselage and the voluminous landing gear fairings the flow field behind the aircraft is highly vortical. Flying in airdrop configuration even aggravates the situation. To comprehensively analyze and evaluate the airdrop capabilities of military transport aircraft DLR has developed a simulation approach, coupling the DLR TAU code with the multibody simulation tool SIMPACK. This approach enables DLR to compute the trajectories of airdropped supplies under full consideration of flow interaction effects. For various cargo and cargo–parachute configurations DLR successfully demonstrated that this approach is well-suited to accurately compute an airdrop sequence. The results of two of these configurations are presented in this paper.

Sven Geisbauer, Hauke Schmidt
Numerical Investigation of Unsteady Tangential Blowing at the Rudder of a Vertical Tailplane Airfoil

A numerical 2D investigationKröhnert, A. of a vertical tailplane airfoil using active flow control with tangential blowing over the rudder shoulder is conducted. The aim of the flow control application is to increase the maximum lift or side force, which can be created by the vertical tailplane, at critical flight conditions like the one-engine-inoperative failure case. In this case the rudder is highly deflected, leading to a large separation on the rudder without blowing. With constant tangential blowing at the rudder shoulder it was shown that fully attached flow can be achieved. To increase the efficiency, pulsed blowing is applied in the present study, leading to a similar increase in the lift coefficient at a reduced actuation mass flow rate requirement. Parameters like the blowing momentum coefficient and the dimensionless frequency are varied and the results are compared to those of the flow calculations with constant blowing. It is observed that pulsed blowing with a small momentum coefficient leads to a strong increase in the lift coefficient compared to constant blowing. The resulting lift increment depends on the dimensionless frequency selected.

Anna Kröhnert
Propeller and Active High Lift Wing Interaction in Experiment and Simulation

Within the German BNF research project a generic twin-engine configuration with an active high-lift wing and modern turboprop engines is investigated. This paper deals with high fidelity RANS computations of the wind tunnel configuration measured in previous measurement campaigns. The simulation data is in good agreement with the experiment. The presented investigations focus on the jet flow due to the internally blown flap and the propeller slipstream.

Carsten Lenfers, Nils Beck, Marc Bauer
Sensitivity of a Low Pressure Ratio Jet Engine Fan to Inlet Distortion

As partTheune, M. of futureSchönweitz, D. civil aircraft concepts the integration of jet engines is considered as an additionalSchnell, R. possibility to increase the efficiency of the whole aircraft. While the ingestion of the fuselage boundary layer reduces the drag of the aircraft it also causes the fan stage of the engine to operate with a distorted inflow. In this study, a fan with a low total pressure ratio, representing future fan designs, and the fan of the International Aero Engines (IAE) V2500 engine, representing a common fan design in today’s jet engines, are imprinted with a parameterized generic but also realistic inlet distortion. The numerical investigation of both fans that employed transient full-annulus simulations showed that regarding different criteria the low pressure ratio fan is more sensitive to the imprinted inlet distortion.

Marius Theune, Dirk Schönweitz, Rainer Schnell

Optimization

Frontmatter
A Consistent and Robust Discrete Adjoint Solver for the SU $$^2$$ 2 Framework—Validation and Application

InSagebaum, M.thisGauger, N.R. work we introduce a robust and consistent discrete adjoint solver that has been embeddedAlbring, T. into the open-source multiphysics framework SU$$^2$$2 by exploitation of the fixed-point structure of the flow solver. At inviscid and turbulent optimization test cases we demonstrate the capabilities of the implementation and compare it with the continuous adjoint method and the common frozen eddy viscosity assumption.

Tim Albring, Max Sagebaum, Nicolas R. Gauger
Comparison of Breguet and ODE Evaluation of the Cruise Mission Segment in the Context of High-Fidelity Aircraft MDO

ThisBecker, R.-G.reportSeider, D.presentsHimisch, J. a multi-disciplinary optimization (MDO) processKruse, M.thatAbu-Zurayk, M.minimizesEinarsson, G. the missionBanavara, N. fuel burn of an aeroelastic long-rangeFührer, T.transportIlić, Č aircraft configuration, by modifying the wing planform, twist, and structural element thicknesses. Two optimizations are performed, one where the fuel burn is approximately evaluated through Breguet range equation, and the other where the ordinary differential equation (ODE) for the step-climb cruise is formally integrated. This is done in order to determine if the Breguet equation is still sufficient in face of high-fidelity aeroelastic simulations. The two optimized designs ended up having similar improvements, thus confirming the applicability of the Breguet equation, for the number of design parameters that were employed.

Časlav Ilić, Tanja Führer, Nagaraj Banavara, Mohammad Abu-Zurayk, Gunnar Einarsson, Martin Kruse, Jan Himisch, Doreen Seider, Richard-Gregor Becker

Turbulence Research and Turbulence Modeling

Frontmatter
Control of the Secondary Crossflow Instability Using Plasma Actuators

Direct numerical simulations are used to investigate the fundamental applicability of plasma actuators for controlling laminar breakdown in a swept-wing-type boundary-layer flow. Localized volume forcing, modelling the actuators, is used to favourably influence the three-dimensional nonlinear disturbance state with large-amplitude crossflow vortices (CFVs). One actuator per fundamental spanwise wavelength is positioned at a selected spanwise position to alter the CFVs and the associated flow field. It is found that both forcing against and in the direction of the crossflow can weaken the secondary instability and thus delay transition to turbulence.

Philipp C. Dörr, Markus J. Kloker
On Phase Asymmetries in Oscillatory Pipe Flow

We present results from direct numerical simulations (DNS) of oscillatory pipe flow at several dimensionless frequencies $$W\!o\in \{6.5,13,26\}$$Wo∈{6.5,13,26} and one fixed shear Reynolds number $$Re_{\tau }=1440$$Reτ=1440. Starting from a fully-developed turbulent velocity field at that $$Re_{\tau }$$Reτ, the oscillatory flow either relaminarises or reaches a conditionally turbulent or strongly asymmetric state depending on $$W\!o$$Wo. The numerical method is validated by demonstrating excellent agreement of our DNS results with experimental data and analytical predictions from literature for the limiting cases of non-oscillating but turbulent and oscillating but laminar pipe flow. For an oscillating turbulent pipe flow we further found a very good agreement between qualitative descriptions of the characteristic flow features observed in experiments and our DNS. Here, we focus on the observation of a strongly asymmetric behaviour between the positive and the negative half-cycles of the oscillatory pipe flow at $$W\!o=6.5$$Wo=6.5.

Daniel Feldmann, Claus Wagner
Generalized Energy Budget Equations for Large-Eddy Simulations of Scalar Turbulence

The energy transfer between different scales of a passive scalar advected by homogeneous isotropic turbulence is studied by an exact generalized transport equation for the second moment of the scalar increment. This equation can be interpreted as a scale-by-scale energy budget equation, as it relates at a certain scale r terms representing the production, turbulent transport, diffusive transport and dissipation of scalar energy. These effects are analyzed by means of direct numerical simulation where each term is directly accessible. To this end, a variation of the Taylor micro-scale based Reynolds number between 88 and 754 is performed. Understanding the energy transport between scales is crucial for Large-Eddy Simulation (LES). For an analysis of the energy transfer in LES, a transport equation for the second moment of the filtered scalar increment is introduced. In this equation new terms appear due to the interaction between resolved and unresolved scales, which are analyzed in the context of an a priori and an a posteriori test. It is further shown that LES using an eddy viscosity approach is able to fulfill the correct inter-scale energy transport for the present configuration.

Michael Gauding, Achim Wick, Jens Henrik Goebbert, Markus Hempel, Norbert Peters, Christian Hasse
Statistical Description of Streamline Segments in a Turbulent Channel Flow with a Wavy Wall

In this study we investigate the statistical properties of so called streamline segments in a turbulent channel flow with one plane and one wavy wall. We give a short overview of the concept of streamline segments and recent results in description and modeling in this field. We find that streamline segments in the vicinity of the wavy wall are significantly smaller on average than in the core region. However, normalizing the length distribution with the mean segment length leads to an almost perfect collapse of the pdfs. This quasi-universal behavior is further highlighted by the comparison to statistics of streamline segments in homogeneous isotropic turbulence. Finally, we investigate the kinematic behavior of streamline segments by means of conditional moments and show differences in scaling behavior compared to the classical structure function analysis.

Fabian Hennig, Jonas Boschung, Norbert Peters
Application of Numerical Wall Functions for Boundary Layer Flows with Separation and Reattachment

This paper describes a numerical wall function method for RANS simulations of isothermal incompressible flows with separation and reattachment using an unstructured flow solver. The method is studied for the Spalart-Allmaras one-equation model and is implemented in OpenFOAM$$\circledR $$®. For each wall node, a one-dimensional boundary-layer problem is integrated numerically on an embedded sub-grid in the near-wall region. The method is applied to the flow over a backward facing step, over a smoothly contoured ramp and over a NACA4412 airfoil to show the improvement of the results compared to universal wall functions.

Tobias Knopp, Fabian Spallek, Octavian Frederich, Gerd Rapin
Simulation of a Helicopter Engine Jet Including a Realistic Nozzle Geometry

AOnur Cetin, M.preliminaryRist, U.numericalMeinke, M.simulationSchröder, W. of a helicopter engine jet at a Reynolds number of Re = 750,000 and a Mach number of M = 0.341 is performed. The influence of a realistic nozzle geometry on the jet properties is analyzed by using highly resolved large-eddy simulations based on hierarchically refined cartesian meshes. To simulate the helicopter engine jet, the interior of the engine nozzle, is included in the flow domain. At the inlet plane synthetic turbulence is prescribed to mimic the exit conditions after the last turbine stage. For the validation of the solution method, a single cold round jet at a Reynolds number of Re = 400,000 and a Mach number of M = 0.9 is computed and the results are compared to reference data.

Mehmet Onur Cetin, Matthias Meinke, Wolfgang Schröder
Large-Eddy Simulation of the Flow Field in a Rotating Axial Fan

Large-eddy simulation (LES) results of the turbulent flow field in a $$72^{\circ }$$72∘ segment of a rotating axial fan are discussed. A newly developed finite-volume flow solver which is based on non-boundary-fitted Cartesian grids is used to solve the three-dimensional flow equations for viscous compressible fluids. Computations are performed for two operating points at a constant Reynolds number of $$9.36 \times 10^5$$9.36×105 based on the outer casing wall diameter. The capability of the method to accurately resolve the main flow phenomena including the unsteady turbulent tip-gap vortices is demonstrated.

Alexej Pogorelov, Matthias Meinke, Wolfgang Schröder
Investigation of the Law-of-the-Wall for a Turbulent Boundary Layer Flow Subject to an Adverse Pressure Gradient Using Particle Imaging

We present an experimental investigation and data analysis of a turbulent boundary layer flow at a significant adverse pressure gradient for two Reynolds numbers $$Re_\theta =6200$$Reθ=6200 and $$Re_\theta =8000$$Reθ=8000. We perform detailed multi-resolution measurements by combining large-scale and long-range microscopic particle imaging. The flow is designed to be close to equilibrium in the sense that characteristic integral flow parameters evolve slowly in streamwise direction to study scaling laws for the mean velocity and for the total shear stress in the inner part of the boundary layer. In the inner part of the inner layer the mean velocity can be fitted by a log-law. We observe larger values for the log-law slope than in zero-pressure gradient flows and study possible history effects. The outer part can be described by a modified log-law, which depends on the pressure gradient parameter and on a parameter for the effect of the mean inertial terms. Finally we present a new composite profile for the mean velocity.

Tobias Knopp, Nicolas A. Buchmann, Daniel Schanz, Christian Cierpka, Rainer Hain, Andreas Schröder, Christian J. Kähler

Laminar Flow Control and Transition

Frontmatter
Numerical Investigation of the Bending of Slender Wall-Mounted Cylinders in Low Reynolds Number Flow

TheAxtmann, G. aim of the present studies is construction of reference data for the prediction of the bending of sensor hairs close to the wall in a boundary-layer flow. Three-dimensional direct numerical simulations (DNS) of finite cylinders in single and tandem configuration are carried out. The numerical setup is guided by a towing-tank experiment performed at the Technical University of Freiberg. All numerical configurations are chosen to complement and extend the experimental work. The bending curve of the cylinders is estimated by a static approach according to 1st-order Euler-Bernoulli beam theory. Based on the forces, extrapolated from the DNS of the flow field, the influence of wall- and top-end effects and Reynolds numbers between 5 and 40 is examined more deeply. Also, varying positions of cylindrical tandem configurations in stream- and spanwise directions are investigated. The present work shows good agreement between simulation and experiment.

Gabriel Axtmann, Ulrich Rist, Franziska Hegner, Christoph Bruecker
Effect of Forward-Facing Steps on Boundary Layer Transition at a Subsonic Mach Number

Experiments were conducted at a subsonic Mach number in the Cryogenic Ludwieg-Tube Göttingen to study the influence of surface imperfections on boundary layer transition. Forward-facing steps of different height were installed on two spanwise invariant wind tunnel models and their effect on transition was examined at high chord Reynolds numbers and various streamwise pressure gradients. Transition, detected non-intrusively by means of the Temperature-Sensitive Paint technique, was found to gradually move upstream towards the step location with increasing step Reynolds numbers and relative step height. Larger flow acceleration had a favorable influence on the transition Reynolds number even in the presence of forward-facing steps, but also increased the sensitivity of boundary layer transition to the surface excrescences. The plots of the relative change in transition location as a function of step Reynolds number and relative step height gave good correlations of the results obtained with both wind tunnel models. The correlations were practically independent of the streamwise pressure gradient. Criteria for allowable tolerances on low-sweep Natural Laminar Flow surfaces can now be established from the functional relations determined in this work.

Marco Costantini, Steffen Risius, Christian Klein, Winfried Kühn
Combined Active Separation Control on the Leading Edge and on the Trailing Edge Flap of a Slatless High-Lift Configuration

ThisHaucke, F.paperBauer, MatthiasdescribesNitsche, W. experimental investigations into active flow control applied at the wing leading edge and at the trailing edge flap of a slatless high-lift wing configuration. The experiments were conducted on an airfoil, which is used extensively by different German and European research programs. The experimental results presented in this work demonstrate successfully the effectiveness of multi-locational active flow control to increase $$c_l$$cl, $$c_{l,max}$$cl,max and $$\varDelta \alpha _{max}$$Δαmax in combined mode.

Frank Haucke, Matthias Bauer, Wolfgang Nitsche
Receptivity of a Swept-Wing Boundary Layer to Steady Vortical Free-Stream Disturbances

Direct numerical simulations (DNS) of steady vortical free-stream disturbances impinging on the leading edge of a swept wing are performed for a low- and a high-speed subsonic case at a Mach number of 0.16 and 0.65, respectively. The receptivity of the crossflow-instability dominated boundary layer downstream of the stagnation line to the forced disturbances is investigated. The introduced (spanwise) wavelengths are in the order of the most amplified steady crossflow mode in the low Mach-number case and induce respective low-amplitude disturbances in the boundary layer.

Holger B. E. Kurz, Markus J. Kloker
Discrete Adjoint Based Optimal Active Control of Separation on a Realistic High-Lift Configuration

ThisÖzkaya, E.paperKramer, F.presentsThiele, F. a frameworkGauger, N.R. for the optimalNemili, A. active separation control mechanism on a realistic high-lift configuration. To control the separation, synthetic jet actuation is applied on the pressure and suction side of a 3D wing with slats, flaps and flap track fairings. Flow control is realised by varying the parameters of actuation like amplitude, frequency, phase shift and blowing angles. An optimal set of actuation parameters that delay the separation and enhance the aerodynamic performance is found by combining a gradient based optimisation algorithm with a discrete adjoint Unsteady Reynolds-averaged Navier Stokes (URANS) solver. A detailed analysis of the sensitivities with respect to the actuation parameters is presented. Optimisation has yielded a noticeable increase in the lift compared to the initial actuated flow.

Anil Nemili, Emre Özkaya, Nicolas R. Gauger, Felix Kramer, Frank Thiele
Nonlinear Disturbance Evolution Downstream of a Medium Height Roughness Element

The present study is devoted to nonlinear mode interactions in the wake of a medium height, isolated roughness placed in a laminar, airfoil boundary layer. Upstream of the roughness low-amplitude, fundamental TS-wave bands are excited. Nonlinear interactions in-between the fundamental modes in the near wake lead to the formation of low-frequency, subharmonic-type modes before the fundamental modes can recover linear stability characteristics with the stabilization of the mean flow. For lower roughness heights the low-frequency modes are only weakly distinct and the disturbance evolution is dominated by the fundamental modes in the roughness wake. With increasing mean flow distortion, that is roughness height, the subharmonic-type modes experience a resonant growth stage in the far wake, which provokes the onset of turbulence. For further increased roughness heights, the fundamental and the subsequent interactions modes reach nonlinear amplitudes in the near wake and, thereby, initiate the laminar flow breakdown before the boundary layer can stabilize.

Benjamin Plogmann, Werner Würz, Ewald Krämer
Leading-Edge Receptivity to Free-Stream Vorticity of Streamwise Corner-Flow

The receptivity of a streamwise corner-flow configuration with super-elliptical leading edges is investigated by means of direct numerical simulations. For this purpose, vortical perturbations are induced into the computational domain upstream of the leading edge to study the influence of frequency and wave obliqueness on perturbation amplification and pattern formation. Additionally, we investigate the flow response to artificial homogeneous and isotropic free-stream turbulence. It is found that the near-corner region is particularly sensitive to vortical disturbances aligned with the free-stream, and prone to the formation of anti-symmetric disturbance patterns that lead to high local amplification levels.

Oliver T. Schmidt, Jennifer Staudenmeyer, Ulrich Rist, Claus-Dieter Munz
IR Measurements for Quantification of Laminar Boundary Layer Stabilization with DBD Plasma Actuators

In-flight experiments for laminar boundary layer stabilization are conducted on a laminar flow wing glove, mounted on a manned motor glider. A single DBD plasma actuator is operated on the pressure side of the glove to delay natural laminar-turbulent transition while an infra red (IR) camera is mounted below the wing allowing a measurement of the spatial development of the transition. Besides the quantification of the flow control result, this article shows postprocessing strategies for perspective camera calibration with curved surfaces, image dewarping and for inhomogeneous surface heating.

Bernhard Simon, Paul Schnabel, Sven Grundmann
Local Stability Analysis of Laminar-Turbulent Boundary Layer Transition on Blunt Generic Re-Entry Capsules

Numerical results on laminar-turbulent transition in the boundary layer of typical re-entry capsules at an angle of attack are presented. Laminar base flow computations were conducted for a blunt body with a pure spherical forebody and for sphere-cone models with varying cone angles at cold hypersonic windtunnel conditions. Stability calculations on first and cross-flow modes were performed and the influence of different forebody shapes on the stability properties are discussed. Pressure gradient distribution along the leeward line of symmetry turned out to be the dominant factor of influence for first-mode transition. The stability results reveal a strong dependency of the obtained cross-flow instability N-factors on the sphere-cone angle.

Alexander Theiss, Martin Lichtmes, Stefan Hein

Rotorcraft Aerodynamics

Frontmatter
Transition Determination on a Periodic Pitching Airfoil Using Phase Averaging of Pressure Data

A method of boundary layer transition measurement is presented for wind tunnel models instrumented with surface pressure taps. The measurement relies on taking a number of theoretically identical measurements at different times and then analysing the standard deviation of the pressures. Due to the slight unsteady movement of the transition position, a peak in the standard deviation of pressure $${\sigma } C_{P_{peak}}$$σCPpeak is found at the transition position, and this is correlated with measurements of the transition position with an infrared camera and hot film anemometers. In contrast to microphone measurements, it is shown that the transition detection works for data which has been low-pass filtered with a cutoff of 1 Hz. The application to static and dynamic transition measurements on static and periodically pitching helicopter rotor blade airfoils at Mach 0.3 is demonstrated.

A. D. Gardner, K. Richter
Validation of a Flow Simulation for a Helicopter Fuselage Including a Rotating Rotor Head

This work presents a detailed analysis of the aerodynamic characteristics for a helicopter fuselage including a skid-landing-gear and a rotating rotor head. Thereby, a special emphasis is set on the rotor head. The results are obtained through numerical simulations based on the incompressible URANS equations. The modelling of the rotating rotor head, including collective and cyclic pitch, is based on a sliding mesh interface in combination with mesh deformation. The numerical simulations are performed under the same conditions and at the same scale as for the existing wind tunnel data. Thus a detailed validation study based on the broad experimental data base could be performed. For this purpose the experimental data base was further extended by rotor phase locked stereo particle image velocimetry measurements.

Moritz Grawunder, Roman Reß, Victor Stein, Christian Breitsamter, Nikolaus A. Adams
Comparison Between Two-Dimensional and Three-Dimensional Dynamic Stall

Numerical computations using the DLR-TAU code investigate the differences and similarities between dynamic stall on the two-dimensional OA209 airfoil and the three-dimensional OA209 finite wing. The mean angle of attack in the two-dimensional computations is reduced to match the effective angle of attack at the spanwise position where in the finite wing computations the dynamic stall vortex starts to evolve. Small variations of the mean angle of attack in the two-dimensional numerical simulations show a change from trailing edge separation only to deep dynamic stall. The analysis of the three-dimensional flow field reveals that after the evolution of the dynamic stall vortex the flow field is split into two parts: 1. High spanwise velocities towards the wing’s root in the region between the plane of the first occurrence of stall and the wing’s root. 2. High spanwise velocities towards the wing’s tip in the region between the plane of the first occurrence of stall and wing tip.

K. Kaufmann, A. D. Gardner, M. Costes
CFD/CSD Trim Coupled Simulation of the HART II Rotor with Higher Harmonic Control

The TAU-HOST coupling chain for Fluid-Structure Interaction (FSI) simulations of active helicopter-rotors is validated by computing the HART II experiment. The result accuracy of the unstructured flow solver TAU is investigated in the case of a rotor which experiences Higher Harmonic Controls (HHC). Investigations are performed by a code-to-code comparison with the experiment, FLOWer-HOST, and literature. Moreover, a time-step study and mesh refinement study were performed but improvement of Blade-Vortex Interaction (BVI) intensity fell short of expectations. Nevertheless, results of rotor controls, blade loads and blade deformation show good agreement with experimental data and are in accordance with literature.

Annika Länger
Experimental Investigation of Dynamic Stall on a Pitching Rotor Blade Tip

Measurements on a pitching finite rotor blade tip are performed. Sectional forces obtained from surface pressure measurements show a significant difference in maximum loads and the extent of hystereses between a section near the parabolic blade tip and two sections further inboard. Different characteristics appear also in the flow topology over the suction side of the airfoil investigated by means of Particle Image Velocimetry (PIV) at these locations.

Christoph B. Merz, C. Christian Wolf, Kai Richter, Kurt Kaufmann, Markus Raffel
Influence of Periodically Varying Incident Velocity on the Application of Semi-Empirical Dynamic Stall Models

The dynamic stall behavior of an OA209 rotorcraft airfoil is examined under the influence of a varying incident velocity. Therefore, a harmonic flow velocity variation is added to the pitch motion of the airfoil in antiphase. Results from two-dimensional unsteady RANS computations are presented for steady and periodic flow velocity. The unsteady flow velocity in the computational domain is generated by a fore-aft motion of the airfoil. Both methods are approximations of the flow conditions a blade section of a helicopter rotor experiences during fast forward flight. Finally, the numerical predicted aerodynamic coefficients are used to investigate the modeling capabilities of semi-empirical formulations for a simultaneous angle of attack and incident velocity change.

Dominik Schicker, Manfred Hajek
Coupled Fluid-Structure Simulations of a Trimmed Helicopter Rotor in Forward Flight

Coupled fluid-structure simulations of high fidelity tools have the potential to deliver a more accurate prediction of the aerodynamic and structural properties of helicopters in forward flight than comprehensive rotor codes. Within this paper the aeroelastic behavior of a trimmed helicopter rotor was investigated using strong and loose coupling approaches. Results of the coupling chains HOST-TAU and SIMPACK-TAU are compared to experimental data from the European GOAHEAD test campaign. The validation test case is a cruise flight condition at Ma $$=$$= 0.204 related to an advance ratio of $$\mu = 0.33$$μ=0.33. Pressure distributions along the blade and blade deflections are in good agreement with experimental results and among the coupling approaches.

S. Surrey, J.-H. Wendisch, F. Wienke

Technical Flows

Frontmatter
Transient Temperature Fields of Turbulent Mixed Convection in an Aircraft Cabin Caused by a Local Heat Source

The impact of a localized, transient head load on the temperature fields in aircraft cabin air flows was investigated in the Do 728 test bed of the German Aerospace Center. Surface and fluid temperatures were analyzed using more than 340 local sensors as well as a grid of polystyrene spheres, which was imaged by an infrared camera. To simulate the impact of the real passengers, thermal passenger dummies were used. The spatial spreading of the heat released by the local source could be characterized for the state of the art mixing ventilation system (MV—mixing ventilation) and a novel ventilation system (CCDV—ceiling based cabin displacement ventilation), which provides fresh air at low momentum through the cabin ceiling. As expected, CCDV provides lower cabin temperatures due to its higher heat removal efficiency. While MV tends to accumulate the heat released by the local source in the passenger zone, warm air is able to ascend to the ceiling more easy at CCDV due to the lower inertia forces. The different amount of inertia forces in the flow between MV and CCDV has a measureable impact on the temporal behavior of the resulting flow patterns during operation of the heat source, which is well reflected in the fluctuations of the temperature elevations.

T. Dehne, J. Bosbach
Numerical Simulation of the Thermal Comfort in a Model of a Passenger Car Cabin

Results of numerical simulations of the air flow including the heat transport, the thermal radiation and the thermal comfort of passengers in a model of passenger car cabin are presented. The computations have been performed by coupling flow simulations conducted with the Computational Fluid Dynamics (CFD) code OpenFOAM with simulations of the heat transport within the passengers using the finite-element code THESEUS-FE. The latter takes into account effects like blood flow, heat transfer through the skin and clothing as well as activity levels and ambient humidity in various layers with different heat transport characteristic. Based on these simulations four different ventilation variants known from the ventilation of aircraft cabins are analysed with respect to their performance regarding the thermal comfort of passengers and the their energy efficiency in future electric cars.

Mikhail Konstantinov, Claus Wagner

Vehicle Aerodynamics

Frontmatter
Rear-End Shape Influence on the Aerodynamic Properties of a Realistic Car Model: A RANS and Hybrid LES/RANS Study

TheJakirlic, S.presentKutej, L.workHanssmann, D. is concernedSchütz, T.withBasara, B.theTropea, C. computational investigation of aerodynamic properties of the so-called ‘DrivAer’ car model representing a ‘generic realistic car configuration’ created by ‘merging’ the original geometries of two medium sized cars from the Audi A4 and the BMW 3 series, Heft et al. [7]. Three down-scaled (1:2.5) configurations differing in the rear-end shape—fastback, notchback and estate back geometries—investigated experimentally at the Institute of Aerodynamics and Fluid Mechanics Technical University in Munich are presently considered. The present numerical study focuses on the application of the ERM-capable (Elliptic-Relaxation Method) eddy-viscosity-based $$\zeta -f$$ζ-f RANS model [6] describing turbulence within the Unsteady RANS (Reynolds-Averaged Navier-Stokes) and the so-called PANS (Partially-Averaged Navier-Stokes) computational frameworks. The latter approach representing a variable-resolution Hybrid RANS/LES (Large-Eddy Simulation) method is formulated and implemented into the CFD software package AVL-FIRE by Basara et al. [3]. The main objective of the present work is to check the models’ feasibility in computing the unsteady flow past the ‘DrivAer’ car configuration. The focus is on the varying structural properties of the flow arising from differently-shaped rear-ends and their impact on the surface pressure distribution and subsequently on the drag and lift force coefficients.

S. Jakirlic, L. Kutej, D. Hanssmann, B. Basara, T. Schütz, C. Tropea
Adjoint-Based, CAD-Free Aerodynamic Shape Optimization of High-Speed Trains

Following Othmer’s work [14] on the continuous adjoint formulation for the computation of sensitivities of incompressible, steady-state, ducted flows, we will introduce an iterative, CAD-free, continuous, adjoint-based shape optimization procedure using gaussian filtered sensitivities and mesh morphing with radial basis function interpolation based on the approach described by [1, 2] for the optimization of the front part of the simplified model of a conceptual, generic high-speed train with respect to drag and pressure wave via single- and multi-objective optimization. We will show that, during pressure wave minimization, it was mainly the area with the widest sidewise extension in the bogie section which was affected by the strongest modifications while, on the other hand, for drag optimization the most sensitive areas and significant changes can be found in the front part of the nose tip section. First multi-objective investigations for two-dimensional testcases will show the influence of weighting and morphing parameters on the optimization process involving objective functions for drag and pressure wave.

Daria Jakubek, Claus Wagner
Large Eddy Simulations of Side Flow Past a Generic Model of a High-Speed Train

Computational fluid dynamics (CFD) has been utilized to investigate straight and side flow over a simplified model of the concept high-speed Next Generation Train of the DLR. Large eddy simulation (LES) with a finite volume method for unstructured grids and a lattice Boltzmann method (LBM) were performed to compare the results. The Reynolds number of the flow was $$\mathrm {Re}=2.1\,\times \,10^5$$Re=2.1×105 and the investigated yaw angle was $$30^\circ $$30∘. The flow fields and the aerodynamic forces predicted with these two different methods are compared for the validation case of the flow past a sphere and the flow around the generic train model. Both approaches yield similar force predictions and exhibit different strengths and weaknesses throughout the computational process which are discussed.

Natalia Kin, Ralf Deiterding, Claus Wagner
Flow Field Analysis of a Detailed Road Vehicle Model Based on Numerical Data

The three-dimensional flow field of a detailed road vehicle model with focus on the importance of engine and underbody representation is studied. Further, issues of vortical flows are explored. Especially the presence of wheels and a detailed underbody has a major impact on the developing flow field. The numerical data provides the necessary insight into the main flow features such as the dominant wake structure typical for a bluff body. URANS simulations accounting for the inherent unsteadiness of the flow were performed in OpenFOAM$$^{{\textregistered }}$$® and were validated with experimental force and velocity field measurements using particle image velocimetry at a corresponding Reynolds number of 3 million. The results for the flow field showing a number of secondary effects interacting with the large areas of separated flow along and downstream of the model are discussed in detail. Another emphasis of the analysis is placed on the dependence of the wake structure on the characteristics of the underbody flow and the accuracy of the integral drag and lift coefficients. The study shows the particular importance of considering the impact of model simplifications on the global flow field of a road vehicle model.

Robin Placzek, Peter Scholz

Aeroelasticity and Structural Dynamics

Frontmatter
Flutter Prediction of a Laminar Airfoil Using a Doublet Lattice Method Corrected by Experimental Data

In this paper a stability analysis of a laminar airfoil is presented and compared to turbulent flow conditions. The flutter system with the two degrees-of-freedom heave and pitch is introduced. The aerodynamic derivatives due to a pitch motion are identified experimentally and two Doublet Lattice correction methods are used to determine the aerodynamic derivatives due to a heave motion. The correction is applied to the local pressure distributions and includes nonlinearities due to transonic flow as well as transitional effects. The resulting aerodynamic derivatives reflect the differences between laminar and turbulent flow as measured in the experiment. An influence of the mean angle-of-attack on the stability boundary is shown for free transition. A comparison of the flutter boundaries for free and fixed transition exhibits a lower transonic dip for free transition. One-degree-of-freedom flutter is found only for free transition.

Anne Hebler, Reik Thormann
Numerical Modeling of Wind Tunnel Walls for the Investigation of Oscillating Airfoils

The numerical modeling of airfoil oscillations in wind tunnels is investigated on the basis of frequency response functions of the flow field due to a forced motion input employing unsteady RANS simulations. The analyzed models reasonably predict the unsteady wind-tunnel wall effects, including the acoustic wind tunnel resonance. For high frequencies, however, the model shows significant spurious fluctuations related to non-physical reflections at the outflow boundary. Therefore, both increasing the distance to the computational boundaries and a nominally less-reflective boundary condition according to Hedstrom (1979, J. Comput. Phys. 30:222–237) are examined leading to slightly improved results.

Christoph Kaiser, Jens Nitzsche
Efficient Modeling of Generalized Aerodynamic Forces Across Mach Regimes Using Neuro-Fuzzy Approaches

In the present work, a nonlinear reduced-order modeling (ROM) approach based on dynamic local linear neuro-fuzzy models is presented for predicting unsteady aerodynamic loads in the time domain. In order to train the input-output relationship between the structural motion and the corresponding flow-induced loads, the local linear model tree (LOLIMOT) algorithm has been implemented. Furthermore, the Mach number is incorporated as an additional input parameter to account for different free-stream conditions with a single model. The approach is applied to the AGARD 445.6 configuration in order to demonstrate the efficiency and fidelity of the proposed method. It is indicated that the ROM-based time domain generalized aerodynamic forces (GAFs) show good agreement with the respective full-order CFD solution (AER-Eu). A further comparison in the frequency domain confirms the validity of the approach. Moreover, the potential of the method for reducing the numerical effort of aeroelastic analyses is highlighted.

Maximilian Winter, Christian Breitsamter

Numerical Simulation/Aerodynamics

Frontmatter
Numerical Simulation of Vortex Roll-Up Processes Using the SSG/LRR- $$\omega $$ ω Model

Vortex roll-up processes at two different wing tip shapes are investigated using the DLR TAU flow solver in combination with a Reynolds Stress Model. The performance of the SSG/LRR-$$\omega $$ω Reynolds Stress Model is hereby explored. Results from simulations are compared to state-of-the-art eddy-viscosity models as well as experimental results from literature and own investigations. The SSG/LRR-$$\omega $$ω model predicts the mean flow much more accurately than the eddy-viscosity models. However, deviations up to $$15\,\%$$15% compared to experiments can be found which are related to an inaccurate prediction of the Reynolds stresses in the inner vortex core.

Sebastian Braun, Anna Uhl, Bernhard Eisfeld, Eike Stumpf
Numerical Aero-Structural Dynamic Simulations of the ASDMAD Wing

A partitionedBrüderlin, M.ComputationalStickan, B. Aero-Structural Dynamics (CASD)Schulze, B. method embedded in the FlowSimulator environment is presented and validated with experimental data from the Aero-Structural Dynamics Methods for Airplane Design (ASDMAD) project. With exception of the wingtip, which is an almost $$90^{\circ }$$90∘ canted winglet, the wing is identical to that from the predecessor project High Reynolds Number Aerostructural Dynamics (HIRENASD). The steady results achieved with the coupling chain agree very well with experimental data from the European Transonic Windtunnel (ETW) tests. During the test campaign, the wing was excited in the root region close to resonance frequency of the first and second bending mode. The experimental data is compared with two unsteady simulation approaches: forced motion computations in the corresponding mode, which neglect the mutual interaction between solid and fluid, and CASD simulations, during which the wing was excited by force couples in the wing root region, like in the experiment. The difference between both simulation approaches is small and both agree very well with the experimental data.

Manuel Brüderlin, Bernd Stickan, Bernd Schulze, Marek Behr
Large Eddy Simulation of Turbulent Thermal Convection Using Different Subgrid-Scale Models

We present a comparison of large eddy simulations of turbulent convection in a cuboidal Rayleigh–Bénard cell. The LES are performed with the dynamic Smagorinsky model in the momentum equation and with the subgrid scale heat transport model by Peng and Davidson [5] in the energy equation. Additionally, LES were conducted with a dynamic scale similarity model used in the momentum and in the energy equation. It was found that in contrast to the scale similarity model, the dynamic Smagorinsky model occasionally produces unphysical temperature values which must be filtered out. Their number can be reduced by increasing the filter ratio in the dynamic procedure. On the other hand, the Smagorinsky model shows a log-like dependency on the filter width ratio for all compared quantities, with the best agreement to DNS with respect to the predicted Nusselt number and SGS heat fluxes for the smallest considered filter width ratio.

Tomasz Czarnota, Tim Wetzel, Claus Wagner
Highly Resolved Simulations of Turbulent Mixed Convection in a Vertical Plane Channel

Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of turbulent mixed convection in a vertical plane channel have been performed with the open source finite volume code OpenFOAM®. Since the agreement of the results of LES obtained with second order accurate central differences in space, implicit time integration and the PISO method for the pressure-velocity coupling to data in the literature was rather poor, additional DNS were performed to identify sources of discretization errors in OpenFOAM®. The comparison revealed errors associated not only with the used eddy viscosity and diffusivity subgrid scale turbulence models used for LES but also with the provided default discretization settings. Changing the latter, it turned out that applying an explicit Leapfrog time integration scheme together with a projection method for the velocity-pressure coupling and a fourth order accurate discretization considerably improved the DNS results. Thus, this combination is also recommended for future LES studies.

Christian Kath, Claus Wagner
Computer Aided Analysis of Preconditioned Multistage Runge-Kutta Methods Applied to Solve the Compressible Reynolds Averaged Navier-Stokes Equations

The development of solution methods to approximate steady state solutions of the turbulent compressible Reynolds-averaged Navier-Stokes (RANS) equations is often based on several heuristics. In general a deep understanding of the power as well as the deficiencies of the methods is missing. It is the goal of this article to present an analysis tool which is applied to many well known solution techniques. The tool is based on Arnoldi’s method to investigate approximations to the spectrum of the linearized equations. Numerical examples will demonstrate the good correlation between the approximate spectrum and the convergence behavior for the nonlinear equations.

Stefan Langer
Adjoint-Based Error Estimation and Mesh Refinement in an Adjoint-Based Airfoil Shape Optimization of a Transonic Benchmark Problem

In this article, we apply a new airfoil shape optimization algorithm based on adaptive higher order Discontinuous Galerkin methods with discretization error control to a 2D benchmark problem of the AIAA Design Optimization Discussion Group. Each flow solution in the optimization process is computed on a sequence of goal-oriented h- or hp-refined meshes until the estimation of the discretization error in a given target quantity (like the drag coefficient) is below a prescribed error tolerance. Furthermore, the optimization is driven by the Sequential Quadratic Programming (SQP) algorithm and the corresponding gradient of the objective function is evaluated via the adjoint approach. Finally, the effect of the discretization error on the quality of the optimized airfoil shapes is investigated.

Ding Li, Ralf Hartmann
Ramifications of Implicit Runge-Kutta Time Integration Scheme

Implicit Runge-KuttaRossow, C.-C. methods are more and more coming into the focus of algorithmic research to increase efficiency when numerically solving the Navier-Stokes equations. In this contribution, three variations of Implicit Runge-Kutta methods proposed so far are investigated: first, for future parallelization efforts a red/black Gauss-Seidel iteration procedure is introduced, and compared to the standard lexicographic Gauss-Seidel iteration similar performance is shown. Second, the implicit Left-Hand-Side operator is simplified such that the method becomes formally independent of the Right-Hand-Side spatial discretization, and by careful formulation similar computation times as with the full first order Jacobian are established. Third, the sensitivity of computation time with respect to the number of global sub-iterations is reduced by introducing local sub-iterations based on the size of the actual residual. Computation of two-dimensional compressible and incompressible, laminar and turbulent airfoil flows using the resulting methods confirms the applicability to different flow cases.

Cord-Christian Rossow
Hybrid LES–URANS Methodology for Wall–Bounded Flows with Synthetic Turbulent Inflow Conditions

The paper is concerned with the employment of synthetic turbulent inflow conditions for an unique hybrid LES–URANS method. The utilization of an explicit algebraic Reynolds stress model for the unsteady Reynolds–averaged Navier–Stokes mode provides a reasonable prediction of the anisotropic near–wall turbulence within the hybrid method. In order to extend the scope of application of the hybrid model for industrially relevant flows, the influence of appropriate inflow conditions is evaluated based on two test cases. The relevance of the utilized inflow generator is presented by comparison of the results of a fully–developed channel flow with periodic boundary conditions and synthetically generated turbulent inflow conditions. As a further demanding benchmark the application of the periodic hill test case in combination with the inflow generator is presented and evaluated.

Stephan Schmidt, Michael Breuer
A Mesh-Free Parallel Moving Least-Squares-based Interpolation Method for the Application in Aeroelastic Simulations With the Flow Simulator

A mesh-free interpolation method for the use in aeroelastic aircraft simulations was implemented. The method is based on a weighted moving least-squares (MLS) approach for solving the spatial coupling problem arising in such problems. The paper presents the fundamentals of the MLS-based method and its advantages over the popular and often-used mesh-free interpolation method of Wendland et al. [1, 2]. Further emphasis is put on the description of the parallel implementation of the MLS-based method. The effectiveness of the method is demonstrated with selected interpolation test cases.

Andreas Schuster, Lars Reimer, Jens Neumann
Development of a Fully Automatic Chimera Hole Cutting Procedure in the DLR TAU Code

In order to simulate relative motion of bodies and to increase flexibility in grid generation of complex configurations, an overset grid technique can be used to couple overlapping grid blocks by interpolation of the flow data. Parts of a component grid that overlap a solid body, have to be excluded from the flow computations. In the previous implementation within DLR’s flow solver TAU this is realized by a hole cutting procedure based on hole definition geometries provided by the user. In this work an automatic hole cutting procedure is implemented in the TAU code, which is based on the intersection of grid edges and surface cells to detect the grid points inside of the body and supports overlapping surface grids. The presented method is demonstrated for two test cases.

Frank Spiering
Towards the Simulation of Trimmed Flight Conditions with Active Engines

A concept is presented for the numerical simulation of trimmed aircraft flight in steady-state conditions under the influence of working engines. An important ingredient in this process is the numerical engine boundary treatment. The engine boundary fluxes were computed following the flux-difference scheme of Roe in combination with an engine-specific definition of the fluid state. An elementary prototype configuration was considered first to verify the steady-state trim procedure in 2D. The desired flight equilibrium was found in a few Newton iterations controlling the engine, the pitch angle and the angle of the horizontal tail plane. Subsequently, a 3D configuration of a generic transport aircraft was considered in cruise conditions. As a first step towards the computation of a steady-state flight equilibrium, the CFD simulation has been performed for an initial configuration with working engines.

Arthur Stück, Ralf Heinrich
Wall Modeled Large Eddy Simulation of a Delta Wing with Round Leading Edge

We performed wall modeled large eddy simulation of the flow field around a delta wing with sweep angle of $$65^{\circ }$$65∘ and round leading edge at angles of attack of $$13^{\circ }$$13∘, $$18^{\circ }$$18∘, and $$23^{\circ }$$23∘. Qualitatively, the numerical simulations correctly predict the flow phenomena for all angles of attack considered. Quantitatively, the results show reasonable agreement with experimental measurements of steady and unsteady surface pressures, velocity distributions, and vortex breakdown position and frequency.

Christian Zwerger, Stefan Hickel, Christian Breitsamter, Nikolaus Adams

Experimental Aerodynamics/Experimental Simulation and Test Techniques

Frontmatter
Rotating Camera System for In-Flight Propeller Blade Deformation Measurements

The behaviour of the blades of a propeller or rotor during operation is crucial for its performance and operational saftey. Particularly the bending and twisting of the blades under load are of high interesst, because they directly influence the local angle of attack and thus the performance of the propeller. Up to now only local deformation measurements by means of strain gauges or acclerometers were feasible. The required cabling thereby limits the maximum number of sensors and thus avoids areal measurements. Furthermore, the application of the sensors can influence the mechanical and aerodynamic properties of the blade. A direct shape or location measurement is also not possible with those techniques. The presented measurement method IPCT (“Image Pattern Correlation Technique”) in addition with the application of the newly developed rotating camera system now enables the non-intrusive measurement of the shape and location of propeller- and rotor blades in-flight with a high accuracy. In the beginning of the paper, the measurement technique and the rotating camera are outlined. Later, the performed ground tests and the conducted flight test activities are described briefly and first measurement results are shown. The major part of the development of the rotating camera was funded by the European Commission within the FP7 project $$\text{ AIM }^{2}$$AIM2 (contract no. 266107).

Fritz Boden, Bolesław Stasicki
Fan Blade Deformation Measurements on the DLR Airbus A320-ATRA by Means of IPCT as Part of the Ground Test Campaign in the Frame of the DLR-project SAMURAI

The Image Pattern Correlation Technique (IPCT) was applied to measure the fan blade deformation of the IAE V2527 engine operating at Maximum Continous Thrust (MCT). The ground test on the DLR research aircraft A320-ATRA was a main part of the DLR project SAMURAI which wanted to use the ‘Synergy of Advanced Measurement Techniques for Unsteady and High Reynolds Number Aerodynamic Investigations’. The stereo camera system was fixed in front of the left engine. For certification reasons the correlation pattern had to be projected to the fan by a laser. The IPCT evaluation were improved to cope with the special challenges of the measurement and to enable a comparison with Computational Structural Mechanics (CSM) results finally.

Tania Kirmse, Sandra Maring, Paul-Benjamin Ebel, Andreas Schröder
Experimental Investigation of Periodically Generated Vortex Rings in Crossflow Impinging on a Flat Plate

In contrast to steady blowing jets, periodically generated vortex rings show great promise for increasing the efficiency of impingement cooling configurations. This study addresses the problem of crossflow superimposed on periodically generated vortex rings impinging on a flat plate. Frequency, duty cycle and equivalent stroke ratio of the vortex rings formed at constant jet-to-crossflow velocity ratio of 4.3 were varied. By means of time resolved PIV measurements, the parameter combinations were assessed with respect to the intensity of wall-bounded vorticity field induced by the vortices at the plate’s surface. Attenuation of the boundary layer renewal is observed if the vortex rings feature a trailing column during their formation. The frequency determines the spacing of subsequent vortices and the intensity of dynamic interaction. Vortex tilting occurs if the frequency is increased and the impact positions are affected. The duty cycle is used to relate the cooling power to the applied mass flux.

Henning Kroll, Armin Weiss, Wolfgang Nitsche
Experimental Determination of Dynamic Derivatives in a Wind Tunnel Using Parameter Identification

For the experimentalRohlf, D.determinationLoeser, T. of dynamic derivatives a new method is presented. Instead of sinusoidal oscillations the models undergoes specifically designed maneuvers on the wind tunnel’s 6 DOF model support. For data evaluation the parameter identification method, as used in flight testing, is employed. The main advantages over the classic approach are significantly reduced testing time and suitability for nonlinear aerodynamic models.

Thomas Loeser, Detlef Rohlf
Development of a Rotor Test Facility for the Investigation of Dynamic Stall

TheRaffel, M.flightRichter, K.envelopeSchwermer, T. of modern helicopters is limited due to unsteady flow phenomena such as dynamic stall. Most investigations regarding this topic, both experimental and numerical, were done on pitching two-dimensional airfoils. Therefore, it is of great interest to investigate the dynamic stall on rotating blades in order to get a better understanding of the unsteady aerodynamics and to improve future rotor designs. A rotor test facility is being built at the DLR in Göttingen. The test rig is integrated into an existing wind tunnel facility and the surrounding conditions were defined. Critical load cases were derived from numerical flow simulations of the rotor blade, and a finite element analysis including a fatigue analysis was performed. A telemetry system is integrated into the rotor head and unsteady pressure sensors are installed in the rotor blades. The development process with its validation and the design of the rotor head and blades are described in this paper.

Till Schwermer, Kai Richter, Markus Raffel
Influence of the Shear Layer Thickness on the Flow Around Unsteady Airfoils

Experiments with a pitching and plunging unsteady airfoil have been conducted in order to investigate the influence of the separating shear layer properties on the formation and detachment of leading edge vortices (LEVs). The chord length was varied from 90 to 180 mm keeping all non-dimensional parameters constant. It has been shown, that the mechanism of vortex detachment changes with chord length, manifested by a change in flow topology. One mechanism scales with chord length, the other is attributed to viscous effects in the boundary layer. For this mechanism a new scaling of the LEV circulation is introduced.

Alexander Widmann, Cameron Tropea

Aeroacoustics

Frontmatter
Towards an Impact-Based Noise Reduction Method for Conceptual Aircraft Design

Aircraft exterior noise is typically reduced by optimizing an isolated aircraft component. The noise emission of this component is optimized with high-fidelity tools or wind tunnel measurements. However, if installed on-board of the aircraft the optimization may not have the desired effect on the total noise impact due to propagation effects or the interaction with other components. Hence, a method is presented, that derives noise reduction requirements for aircraft components based on the total aircraft noise impact. The method is implemented in a parametric aircraft noise prediction tool and applied to a reference aircraft. The aim is to use the noise requirements within conceptual aircraft design to obtain low-noise aircraft in a target-oriented way. Ultimately, this may be a first step towards a noise-to-design process.

Jason Blinstrub, Lothar Bertsch
Overset DNS with Application to Homogeneous Decaying Turbulence

In this contribution an application of a computational aeroacoustics code as a hybrid Zonal DNS tool is presented. The derivation of the Non-Linear Perturbation Equations (NLPE) extended with viscous terms is shown as well as information related to the numerical method is given. The application of the simulation tool to a generic three-dimensional test case, i.e., the Taylor-Green Vortex (TGV), is presented. This TGV, initially consists of only one length scale, develops into homogeneous decaying turbulence. Results of energy spectrum and grid convergence study are given. It is shown that the observed accuracy of the numerical code matches well with the expected theoretical order of four.

R. A. D. Akkermans, N. Buchmann, J. Dierke, R. Ewert
Direct Numerical Simulation of Tonal Noise in Sub- and Transonic Airfoil Flow

Tonal noise phenomenon is studied by Direct Numerical Simulation of the sub- and transonic flow around the symmetric NACA 0012 airfoil. A fifth-order Weighted Essentially Non-Oscillatory and a fourth-order explicit Runge-Kutta scheme are utilized. A main focus of this paper is the validation of the method and a grid study for an airfoil flow at a moderate Reynolds number. Therefore, the results of a Direct Numerical Simulation of subsonic flow are compared to experiments. Both, the results of the numerical and experimental flow show the tonal noise phenomenon. The interaction of the Tollmien-Schlichting waves and the trailing edge is studied visually enabling to easily understand the physical principles of the tonal noise phenomena. Additionally, for a transonic flow the non-linear pressure wave propagation, merging and frequency shift is considered.

Manuel A. Gageik, Igor Klioutchnikov, Herbert Olivier
Numerical Simulation of Turbulence Induced Flow Noise in Automotive Exhaust Systems Using Scale-Resolving Turbulence Models

As a first step for a general numerical method for exhaust noise prediction a simplified generic exhaust system model, the straight pipe, has been investigated in terms of turbulence induced flow noise. Impinged with a constant mass flow rate, the dominant acoustic source mechanism was reduced to the subsonic jet behind the orifice at a Mach number of $$\text {M}_{\text {j}}=0.3$$Mj=0.3. In order to calculate the radiated jet noise, detached eddy simulations have been carried out to receive transient data of the turbulent flow field. Afterwards these data were used for the calculation of the acoustic far-field, based on the Ffowcs Williams-Hawkings acoustic analogy. Additionally experimental investigations of the turbulent flow as well as the acoustic far-field have been carried out in order to validate the numerical results. The acoustic results offered a good prediction of the sound pressure level at high frequencies compared to experimental data. Otherwise partially high deviations were depicted in the lower frequency range. The study of the turbulent flow field showed, that the delay of the development of turbulent structures at the jet beginning, caused by the absence of initial turbulent fluctuations, is a possible reason for this overestimation. Due to these dominant low-frequency components, the overall sound pressure level also offered an overestimation, but a good prediction of the directivity of the sound pressure field.

Jan Hillenbrand, Stefan Becker, Thomas Sailer, Martin Wetzel, Oliver Hausner
Flap Side-Edge Noise Prediction Within Conceptual Aircraft Design

AircraftRamdjanbeg, M.R.noiseRossignol, K.-S. analysis hasSimons, D.G.beenBertsch, L. a principal topic regarding environmental issues for aviation industry and research community. Besides noise abatement procedures the focus is leaning more towards reduction at the source itself. Noise prediction for optimization purposes of existing technologies as well as integration within design processes of aircraft is required more than ever. Relatively new and still under development, yet already proven to be beneficial is the approach of noise prediction within conceptual aircraft design. To succeed it requires a componential and parametric prediction approach with dominating noise sources adequately represented and modeled. One missing source in such a prediction scheme is the flap side edge. Recent research efforts have again indicated potential dominance of this noise source. Due to complexity of the source mechanisms and practicability limitations it is difficult to investigate the contribution of the flap side edge on the overall aircraft noise. Therefore, a parametric and componential simulation approach is applied to perform a flap side edge noise analysis. For this purpose a semi-empirical prediction model is implemented within an existing parametric aircraft noise analysis module. The aim of the current research study is to analyze the flap side edge noise and provide more insight and knowledge of its potential dominance.

M. R. Ramdjanbeg, L. Bertsch, K.-S. Rossignol, D. G. Simons
A Hybrid Discontinuous Galerkin-Finite Volume Method for Computational Aeroacoustics

A hybrid method for a fully coupled determination of aerodynamic sound is introduced. From the instantaneous velocity and vorticity, determined by approximate solutions of the Navier-Stokes equations, acoustic source terms are obtained, which are plugged into the acoustic perturbation equations being solved with a high-order discontinuous Galerkin method. The coupling method is discussed in detail and results of validation tests of the aeroacoustics solver are presented.

Michael Schlottke-Lakemper, Matthias Meinke, Wolfgang Schröder
Identification of Sound Sources in Ducted Flows with an LES-SI-DMD Approach: Influence of Mesh Refinement and Subgrid Scale Models

A novel computational approach for the prediction of aeroacoustic sources based on Large Eddy Simulation and System Identification is presented. The objective is to characterize concurrently both the scattering of acoustic waves and the generation of noise at flow discontinuity in a duct. The methodology is outlined and applied to an orifice placed inside a pipe with turbulent flow. Results for the passive acoustic scattering are compared with experiment. The noise sources obtained from LES with and without an external acoustic excitation are compared for a variety of simulation settings. The influences of mesh resolution and of the subgrid scale models are investigated. Flow features responsible for noise generation are educed with dynamic mode decomposition.

Carlo Sovardi, Wolfgang Polifke
Flow-Induced Noise of a Forward-Backward Facing Step

This work deals with the aeroacoustic sound radiated by a forward-backward facing step. A large eddy simulation with coupled aeroacoustic computation was carried out. In addition, acoustic measurements in an acoustic wind tunnel were conducted and compared with the numerical results. The sound radiation of the step geometry is dominated by broadband noise. The results show that the simulation is able to capture the acoustic field and the numerical results enable the identification of flow regions responsible for sound generation.

Matthias Springer, Christoph Scheit, Stefan Becker
Experimental Investigations of Tonal Noise on a Vehicle Side Mirror

ExperimentalWürz, W. investigations on an isolated vehicle side mirror model are performed in a low turbulence wind tunnel aiming at the identification of the acoustic source mechanism leading to tonal noise emission. A combination of acoustic measurements and Particle Image Velocimetry shows that the discrete frequency noise can be related to the presence of a laminar boundary layer separation extending up to the trailing edge on the mirror’s side surface and upper side. In the vicinity of the trailing edge, the shear layer develops into a vortical structure, which impinges on the trailing edge. By utilization of Proper Orthogonal Decomposition on the ensembles of instantaneous velocity fields and application of a phase sorting method, the length scales of the vortical structures could be extracted and related to the acoustic radiation. Order of magnitude analyses show parallels to the acoustic feedback mechanism known from the NACA 0012 airfoil.

Maike Werner, Werner Würz, Ewald Krämer
Towards Adjoint-Based Trailing-Edge Noise Minimization Using Porous Material

In this paper, we present a discrete adjoint-based optimization framework to obtain the optimal distribution of the porous material over the trailing edge of a 3-D flat plate. The near-body strength of the noise source generated by the unsteady turbulent flow field is computed using a high-fidelity large-eddy simulation (LES). The design gradients are computed using the forward and reverse modes of automatic differentiation (AD). The increase of memory requirement in the reverse mode AD is alleviated by checkpointing. We show, by optimally controlling the material porosity and permeability, it is possible to minimize the turbulence intensity responsible for noise generation at the trailing edge and thus significantly reduce the radiated noise.

Beckett Y. Zhou, Nicolas R. Gauger, Seong R. Koh, Matthias Meinke, Wolfgang Schröder

Hypersonic Aerodynamics

Frontmatter
Numerical Simulation of the Flow and Combustion Inside the Reaction Chamber of the AHRES Hybrid Rocket Engine

Within the AHRES program of DLR, the Institute of Aerodynamics and Flow Technology is developing a software tool for the design of hybrid rocket engines. Therefore, the Department Spacecraft is operating a lab-scale hybrid rocket engine for ground tests with high test peroxide (87.5 wt.%) as liquid oxidizer and hydroxyl-terminated polybutadiene with aluminum additives as solid fuel. Within this study, the flow field and the combustion process inside the reaction chamber of the AHRES hybrid rocket engine are computed using numerical simulations. Namely, three characteristic points in burning time are determined within 2D axial symmetric steady-state simulations. These simulations are carried out applying the DLR TAU-Code with the implemented reaction models for chemical equilibrium and non-equilibrium conditions.

Stefan May, Ognjan Božić
Interaction of Acoustic and Entropy Waves with Shocks

TheSchröder, W.interactionMeinke, M. of acousticSchilden, T. and entropy waves with an oblique shock occurring upstream of a cone is investigated. The three-dimensional supersonic Ma $$=$$= 5.9 flow over a $$30^{\circ }$$30∘ half angle cone at prescribed acoustic and entropy waves is computed and the wall pressure fluctuations are sampled to quantify the receptivity with respect to the incident waves. Two cone configurations with different tip radii are considered to determine the influence of the tip radius on the wall pressure fluctuations. It is shown that the receptivity to both types of waves shows a weak dependence on the cone tip radius that decays in the downstream direction.

Thomas Schilden, Matthias Meinke, Wolfgang Schröder

High-Agility Configuration

Frontmatter
Dynamic Actuation for Delta Wing Post Stall Flow Control

The manipulation of delta wing flow by active and passive flow control methods is of great interest for increasing the performance (e.g. lift enhancement) of such configurations. This work presents experimental results in the post-stall regime at very high angles of attack ($$\alpha =$$α= 35–$$45^\circ $$45∘) on a $$65^\circ $$65∘ sweptback generic half delta wing configuration (VFE-2 geometry) with sharp leading edge using slot actuators for pulsed blowing along the leading edge. The study comprises results of force, velocity and pressure measurements and substantiates the receptivity of the shear layer for the pulsed excitation. For $$\alpha = 35^\circ $$α=35∘, an actuation at $$F^{+} \approx 2.7$$F+≈2.7 effects a retardation of vortex breakdown. For $$\alpha = 45^\circ $$α=45∘, the optimum pulse frequency was found at $$F^{+} =$$F+= 1.0–1.5, which leads to the re-establishment of a burst vortex and a significant increase in lift, thus satisfying the aim of enhancing aerodynamic performance.

Anja Kölzsch, Sophie Blanchard, Christian Breitsamter
CFD Study on a Pitching Missile with Respect to Reduce the Phantom Yaw Effect

ThisSchnepf, C.numericalSchülein, E. study is about the alleviation of the Phantom Yaw Effect on a pitching missile. A pair of slit shaped side jets, so called aerostrakes is used to force a symmetric separation at the shoulder of the missile. The unsteady Reynolds averaged Navier-Stokes equations are solved with a two equation turbulence model for a case with and without aerostrakes. The missile is pitching sinusoidally at a frequency of 5 Hz between $$0^\circ \le \alpha \le 44^\circ $$0∘≤α≤44∘ at Mach 0.8. The results show that the magnitude of the side force, resulting from Phantom Yaw, is reduced by the aerostrakes and the onset angle for the PYE is shifted to higher angle of attack. A reversal of sign of both the side force and yawing moment is also prevented when using the aerostrakes. Furthermore, the influence of the pitching motion on the relevant aerodynamic coefficients is less profound in the case with aerostrakes.

Christian Schnepf, Erich Schülein

Wind Energy

Frontmatter
An Adaptive Lattice Boltzmann Method for Predicting Wake Fields Behind Wind Turbines

The crucial components of a dynamically adaptive, parallel lattice Boltzmann method are described. By utilizing a level set approach for geometry embedding the method can handle rotating and moving structures effectively. The approach is validated for the canonical six degrees of freedom test case of a hinged wing. Subsequently, the wake field in an array of three Vestas V27 wind turbines at prescribed rotation rate and under constant inflow condition is simulated for two different scenarios. The results show that the low dissipation properties of the lattice Boltzmann scheme in combination with dynamic mesh adaptation are able to predict well-resolved vortex structures far downstream at moderate computational costs.

Ralf Deiterding, Stephen L. Wood
Aerodynamic Design and Optimization of a High-Lift Device for a Wind Turbine Airfoil

UnderManso Jaume, A. the framework of the BMWi funded Smart Blades project, concerned with the development of intelligent wind turbine rotor blades, the design and numerical optimization of a leading edge slat for the DU 91-W2-250 airfoil, included in the Smart Blades reference blade, have been accomplished. Two different design cases were investigated: an integrated slat and a superimposed one. The position and shape of both slats were optimized, fulfilling in both cases the objective of improving their aerodynamic performance in terms of stall delay and efficiency. In comparison to the original airfoil, the improvement in aerodynamic performance achieved by the implementation of a leading edge slat provides a glimpse of the potential benefit of using these devices in wind turbine blades.

Ana Manso Jaume, Jochen Wild
Investigations on the Wake Development of the MEXICO Rotor Considering Different Inflow Conditions

The presented studies focus on the numerical analysis of the three bladed MEXICO model wind turbine rotor regarding the wake development under different inflow conditions. One-third-model approaches are used to study grid and numerical effects of the rotor set-up before. Based on this knowledge, a full-model is created and unsteady CFD (Computational Fluid Dynamics) simulations are performed. Moreover, an investigation into the MEXICO measurement data is done in order to answer open questions of previous examinations. The goal of the studies is to simulate wake effects more accurately for different complex cases including yawed inflow.

Christoph Schulz, Konrad Meister, Thorsten Lutz, Ewald Krämer
Stroke-Wing Engine with Dual Wings for Extracting Power from an Airstream

An oscillating wing exposed to a uniform fluid flow and performing a coupled plunging and pitching motion either produces thrust or extracts energy. The amplitude ratio of the two degrees of freedom determines the respective mode. A stroke-wing engine operates in the mode in which energy is gained. The stroke-wing engine with dual wings enhances the efficiency of the single wing machine. Two wings work in opposite direction and take advantage of the interference effects between the neighbouring wings. Numerical and experimental results are presented for a stroke-wing engine with dual wings. The technology carrier DualWingGenerator operates in air and is intended to compete with wind turbines at selected sites with medium-range wind velocities.

Wolfgang Send
Backmatter
Metadaten
Titel
New Results in Numerical and Experimental Fluid Mechanics X
herausgegeben von
Andreas Dillmann
Gerd Heller
Ewald Krämer
Claus Wagner
Christian Breitsamter
Copyright-Jahr
2016
Electronic ISBN
978-3-319-27279-5
Print ISBN
978-3-319-27278-8
DOI
https://doi.org/10.1007/978-3-319-27279-5

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