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This book reports on the latest developments in computational fluid dynamics and turbulence modeling, with a special emphasis on hybrid RANS-LES methods and their industrial applications. It gathers the proceedings of the Sixth Symposium on Hybrid RANS-LES Methods, held on September 26-28 in Strasbourg, France. The different chapters covers a wealth of topics such as flow control, aero-acoustics, aero-elasticity and CFD-based multidisciplinary optimization. Further topics include wall-modelled Large Eddy Simulation (WMLES), embedded LES, Lattice-Bolzman methods, turbulence-resolving applications and comparisons between LES, hybrid RANS-LES and URANS methods. The book addresses academic researchers, graduate students, industrial engineers, as well as industrial R&D managers and consultants dealing with turbulence modelling, simulation and measurement, and with multidisciplinary applications of computational fluid dynamics.

Attached and Detached Eddy Simulation

ADES is not a new concept, but it represents a significant evolution from the original or “Natural” DES concept (NDES), and we believe it could become widespread and the basis for turbulence treatment in most high-Reynolds-number applications once the computing power is sufficient. Therefore, its potential and the likely difficulties inherent in it deserve a detailed discussion.

Philippe R. Spalart, Mikhail K. Strelets

Progress in Hybrid Temporal LES

In order to favour the modelling of the subgrid stresses in continuous hybrid RANS/LES methods, the comparison of the solutions with experimental or DNS databases, and eventually the understanding of the phenomenology observed in the resolved motion, defining a rigorous formalism for such methods is highly desirable [18].

Rémi Manceau

Stress-Blended Eddy Simulation (SBES)—A New Paradigm in Hybrid RANS-LES Modeling

A new global hybrid RANS-LES methodology will be presented. It is intended as replacement for existing models like DES/DDES/IDDES. The new model offers improved shielding of RANS boundary layers, a more rapid RANS-LES ‘transition’, WMLES capabilities as well as modularity with respect to the combination of different RANS and LES formulations.﻿﻿

F. Menter

Consistent Strain/Stress Lag Eddy-Viscosity Model for Hybrid RANS/LES

The paper presents a comparison of two hybridization techniques between RANS and LES, and their potential and limitations in an industrial context. The first part of the paper also attempts to address an often eluded problem in the hybrid RANS/LES scommunity: the importance of the baseline statistical model. A new robust low-Reynolds number eddy-viscosity model, derived from a Reynolds-stress model and accounting for the lag between stress and strain is extended to Detached Eddy Simulation (DES), and compared with the most widely used DES model. The potential of a dual-mesh approach, where statistical and scale-resolving simulations are performed on separate grids, with drifts terms allowing to recover the most accurate solution on each grid, is also assessed on a simple case.

Sylvain Lardeau

Improved Delayed Detached-Eddy Simulations of Actively Controlled Flow

In this study, Improved Delayed Detached-Eddy Simulations (IDDES) were conducted for active flow control with a harmonic actuation on a backward-facing step (BFS) and pulsed blowing on a NACA0015 airfoil for reattachment and separation controls. By using Dynamic Mode Decomposition, the characteristic physical modes of the unexcited flow have been extracted for both cases. With better understanding of unsteady flow features, effective control practices were illustrated. For the BFS case, the optimum excitation frequency was found identical with the step-mode frequency of the baseline flow. Such harmonic actuation enhanced the pairing process, forming the largest scale spanwise coherent structures in the free shear layer, resulting in 40% the maximum reduction of the bubble length. For the airfoil case, with the optimum excitation frequency that determined by the vortex-shedding mode of the baseline flow, 194% the increase of the lift-to-drag ratio was obtained.

Liang Wang, Ruyun Hu, Liying Li, Song Fu

Effect of Upstream Turbulence on Single and Dual-Stream Jets. Assessment of Zonal Detached Eddy Simulation (ZDES)

This paper aims at investigating the effect of upstream turbulence (for instance coming from the engine’s internal geometry) on the jet flow development. Simulations are performed using ZDES [4] combined with synthetic turbulence generation methods. Two cases are studied: an incompressible, single-stream jet and a compressible dual-stream one. It is shown that the upstream turbulence reduces the RANS-to-LES transition and improves the prediction of the location of the shock-cells and global jet flow development, which advocates a systematic consideration of realistic nozzle exit conditions in eddy-resolving simulations.

F. Gand, J. Verrière, S. Deck

Implementation and Assessment of the Synthetic-Eddy Method in an Unstructured Compressible Flow Solver

This paper presents the recent implementation and assessment of the Synthetic-Eddy Method and its divergence-free version in the unstructured compressible DLR-TAU solver. Synthetic turbulence can either be injected at the inflow or at interface planes inside the flow domain, which are defined via simple user input. The methods are successfully applied to quasi-2D flow cases of varying complexity, ranging from a flat-plate boundary layer up to a 3-element airfoil near stall. The simulations yield satisfying agreement with mean-flow reference data, but still leave room for improvements of the adaptation length to fully-developed turbulence.

Axel Probst

Hybrid RANS/LES Simulation Strategy for High-Lift Applications with Disturbed Inflow

This paper presents a strategy to investigate the influence of inflow disturbances on the performance of high-lift airfoils in numerical simulations. The method relies on the algebraic delayed detached-eddy simulation (ADDES), which alows a flexible introduction of synthetic turbulence to trigger the scale resolving mode of the turbulence model. First it is shown that the flow separation is sensitive to the position of the synthetic turbulence injection. Then the ability of the method to predict the influence of a generic vortex on a DLR F15 two-element airfoil is demonstrated.

Silvia Probst

Grey-Area Mitigation Using Commutation Terms at the Interfaces in Hybrid RANS-LES Modeling

With the aim to mitigate the grey area at the RANS-LES interface, the effect of commutation terms is investigated. Simulations of fully developed channel flow and spatially developing boundary layer flow are presented using the commutation terms at the RANS-LES interfaces. The commutation terms are added as source terms in the k, $$\omega$$ω and momentum equations of a zonal RANS-LES model. It is concluded that as an inlet in embedded LES of the developing boundary layer flow, the use of the proposed commutation terms are needed for the LES simulated flow to accurately predict the skin friction. However, it is demonstrated for flows where the RANS-LES interface aligns with the mean flow direction that the effect of the proposed interface methodology is weak.

Sebastian Arvidson, Lars Davidson, Shia-Hui Peng

Scale-Resolving Simulations Based on a Lattice-Boltzmann Method

This paper gives an overview on the scale-resolving capabilities of the Lattice-Boltzmann Method as implemented in the solver PowerFLOW. The basic concept of the approach is outlined, which comprises the turbulence modelling strategy. Following this are three examples ranging from fundamental to geometrically complex test cases: a shear layer, the flow over the NASA Hump and the flow over an iced airfoil. It is shown for all cases that transition from modelled to resolved turbulent fluctuations is achieved automatically once the flow separates with a flow based sensor if grid resolution is sufficient. Agreement with experimental reference data is good. As this paper is only intended to give a general overview, additional insight into each case is available in the corresponding reference papers.

Benjamin Duda, Ehab Fares, Benedikt König

Gas-Kinetic Scheme for Multiscale Turbulence Simulation

Based on the extended BGK equation, the gas-kinetic scheme (GKS) is developed for fine simulation of high-Reynolds-number turbulence. With the help of existing hybrid RANS/LES models to approximate the effective relaxation time, two extended schemes, GKS-DES/IDDES are constructed and show good performances in typical turbulent flow around a cylinder with $$\text {Re}_D=3900$$ReD=3900. Furtherly, a new multiscale method MS-GKS is proposed based on the multiscale evolving solution of extended BGK equation and preliminary tests reveal its strong competitiveness compared with IDDES.

Shuang Tan, Qibing Li, Song Fu

Effects of Convection Schemes on Hybrid RANS-LES Calculations

Nowadays it is commonly accepted to report on convections schemes in the case of Large Eddy Simulations. However, this is still not mandatory for the hybrid Reynolds-Averaged Navier-Stokes (RANS)—LES calculations. Therefore, this paper intends to show that the effects of convection scheme is equally important for hybrid RANS-LES calculations as well as for LES runs. We choose here the Partially-Averaged Navier–Stokes (PANS) model as the representative hybrid RANS-LES model but the conclusions derived in this work are equally applicable to other methods. The aim of the paper is to provide a proper criterion from the employment of higher order differencing schemes. The paper will assess two approaches, namely step functions where central-differencing scheme is used in the regions with a lower unresolved turbulent kinetic energy and a continuous function which depends on the ratio between unresolved and total kinetic energy. The results will be presented for the flow around the square cylinder. Direct numerical simulation (DNS) data and measurements are available for comparisons.

B. Basara, Z. Pavlovic, S. Krajnovic

Application of a Stochastic Backscatter Model for Grey-Area Mitigation in Detached Eddy Simulations

Detached eddy simulations may suffer from so-called grey areas where the model is in LES mode but resolved turbulence is still lacking. A new stochastic backscatter model has recently been proposed and shown to be effective in grey-area mitigation for basic test cases in combination with a high-pass filtered subgrid-scale model. Here, this approach is applied to two cases with more complex flow patterns: a delta wing at high angle of attack showing vortex breakdown and a three-element airfoil. For both cases, significant grey areas are effectively prevented.

Johan C. Kok

On Scale-Resolving Simulation of Turbulent Flows Using Higher-Accuracy Quasi-1D Schemes on Unstructured Meshes

The paper is focused on the scale-resolving simulation of turbulent flow using quasi-1D schemes on unstructured meshes. The numerical algorithm is based on the Edge-Based Reconstruction (EBR) scheme possessing higher accuracy and moderate computational costs on unstructured meshes. We discuss issues related to the application of low-dissipative version of EBR scheme for the scale-resolving simulation on anisotropic meshes. Some techniques which improve the scheme robustness are proposed. The feasibility of the developed numerical algorithm is demonstrated on the two cases. The first problem is immersed subsonic unheated round jet, $$\mathrm{{M}}_{jet}=0.9$$Mjet=0.9, $$\mathrm{{Re}}_D=1.1\times 10^6$$ReD=1.1×106. The second one is turbulent flow over M219 cavity $$\mathrm {M}_\infty =0.85$$M∞=0.85, $$\mathrm{{Re}}_H=1.37\times 10^6$$ReH=1.37×106. The results are in a good agreement both in aerodynamic and acoustic characteristics with the corresponding experimental data. The computations show a strong sensitivity of the results of scale-resolving simulations to the numerical scheme in use and confirm a need in its careful adjustment.

Alexey Duben, Tatiana Kozubskaya

On the von Karman Length Scale as a Triggering Parameter in Eddy-Resolving Simulations of Turbulent Flows

The von Karman length scale $${\text{L}}_{\text{vK}} =\upkappa{\text{S}}/\left| {\nabla^{2} {\text{U}}} \right|$$LvK=κS/∇2U represents a key element in triggering the flow to generate resolved turbulence in Scale-Adaptive Simulations (SAS) [8, 9, 12] analog to the role of grid spacing $$\Delta \left( { = \sqrt[3]{{\Delta _{\text{x}}\Delta _{\text{y}}\Delta _{\text{z}} }}} \right)$$Δ=ΔxΔyΔz3 in Large-Eddy Simulation (LES). Accordingly, the $${\text{L}}_{\text{vK}}$$LvK parameter mimics the length scale characterizing the resolved motion within the SAS framework. It represents a flow variable of decisive importance in additional source term providing selective enhancement of the dissipation rate production, mostly in the separated shear layer regions. The main objective of the present work is the visualization of the structural properties of the $${\text{L}}_{\text{vK}}$$LvK length scale in some internal and external flow configurations subjected to different straining originating from the boundary layer separation from sharp-edged and continuous curved surfaces. Furthermore, the present work attempts to establish a relationship between the $${\text{L}}_{\text{vK}}$$LvK length scale and grid resolution (in terms of grid spacing $$\Delta$$Δ) in relation to the flow unsteadiness characterization, identifying the SAS method capabilities of capturing appropriately the fluctuating turbulence.

Recent Results with Grey-Area Improved DDES for a Wide Range of Flows

At the previous HRLM Symposium we presented a novel DES-based approach [4] that addresses one issue frequently encountered for hybrid RANS-LES methods, i.e. the delayed transition from RANS to LES in separated shear layers also known as the grey area. The approach is based on employing a different sub-grid scale model (i.e. the $$\sigma$$σ LES model of Nicoud et al. [6]) for the LES mode of delayed DES (DDES), which offers an ameliorated behaviour in the crucial early shear layer region. Results are presented for basic calibration cases as well as a range of complex applications featuring different flow topologies, where a comparison is drawn to a current state-of-the-art hybrid method, i.e. standard DDES of Spalart et al. [11]. The new DDES variant is found to improve predictive accuracy significantly for cases strongly impacted by the grey area (e.g. a compressible round jet, flow over delta wing) and at the same time maintains key advantages of the original DDES method, such as its non-zonal nature and its capability to shield attached RANS boundary layers.

M. Fuchs, C. Mockett, J. Sesterhenn, F. Thiele

Hybrid Simulation of High-Reynolds Number Flows Relying on a Variational Multiscale Model

We are interested in the study and improvement of the LES component in hybrid RANS-LES formulations. These models are not designed for blunt-body flows with laminar boundary layers, but it is interesting to examine how they behave in that case. A DDES model is compared with a dynamic Variational multi-scale (DVMS) LES model for two subcritical flows past a cylinder. We then propose a hybridation restricting to DVMS in LES regions. The performances of the different options are compared for subcritical flows and for a flow around a tandem cylinder.

Emmanuelle Itam, Stephen Wornom, Bruno Koobus, Alain Dervieux

Assessment of Scale-Resolving Simulations for Turbomachinery Applications

The application of scale-resolving turbulence representations in turbomachinery promises significantly improved predictions over the classical steady RANS approaches. The scale-resolving models available in the DLR solver for turbomachinery applications TRACE are presented and evaluated using three testcases, viz. a circularX cylinder mounted in a square channel, a 2D streamwise-periodic channel with one wall having hill-shaped features and a low-speed compressor cascade with a tip gap. Results are compared to RANS and URANS predictions and conclusions are drawn.

M. Franke, C. Morsbach

Comparison of Hybrid RANS/LES Methods for Supersonic Combustion in a Model Scramjet Combustor

Numerical studies are carried out on the boundary layer behavior on a flat plate as well as on the non-reactive and reactive flows in a scramjet combustor to analyze the effects of various hybrid RANS/LES methods. Three hybrid RANS/LES methods are selected—an improved delayed detached eddy simulation, the l2ω-detached eddy simulation, and the dynamic l2ω-detached eddy simulation. The present method is based on the finite-volume approach on structured mesh, and the governing equations are treated using the Favre averaging approach. Inviscid fluxes are discretized using 5th order WENO schemes. Turbulent combustion is modeled as a level-set flamelet model. Based on the results from the flat plate and the non-reacting and reacting simulation, most of the hybrid RANS/LES methods show equivalent trends. However, dramatic differences are found in the calculations for the improved delayed detached eddy simulation and dynamic l2ω-detached eddy simulation in terms of eddy capturing.

Junsu Shin, Hong-Gye Sung

Computational Investigation of a Swirled Premixed Burner Using Hybrid RANS-LES Method

High turbulent swirling reacting flow is investigated in a swirled premixed burner using hybrid RANS-LES method. The hybrid method is the Detached Eddy Simulation (DES) and it is combined with the Finite-Rate/Eddy Dissipation (FR/EDM) combustion model to treat turbulence-chemistry interaction. The instantaneous flow fields are well captured by DES and the premixed flame is well reproduced by FR/EDM. It is shown that DES is capable to reproduce the experimental profiles of the mean axial velocity and temperature. Phase-angle analysis of the instantaneous flow field shows the presence of large-scale coherent structures. Q-criterion is used to visualize the 3D behaviour of the structures; it is found that the unsteady flow contains a Precessing Vortex Core (PVC) and Secondary Outer Vortex (SOV).

Z. Mansouri, T. Boushaki, M. Aouissi, I. Gökalp

Assessment of Turbulence Models for Flow Around Three-Dimensional Geometries

This paper presents a computational study of flow around three-dimensional geometries as the Ahmed body, which is a classical test case for automotive flow, but also as the JBC (Japan Bulk Carrier)which was first investigated in the framework of the Tokyo 2015 Workshop on Numerical Ship Hydrodynamics. For both test cases, an investigation of RANS ($$k-\omega$$k-ω SST and EARSM) and hybrid RANS-LES models (DES and IDDES) is conducted. All simulations have been performed with the ISIS-CFD flow solver, which is developed by Ecole Centrale de Nantes and CNRS. For both geometries, the hybrid RANS-LES models predict a high level of turbulent kinetic energy which is in better agreement with the experiments than the quantity predicted with a RANS turbulence model.

E. Guilmineau, G. B. Deng, P. Queutey, M. Visonneau, J. Wackers

Comparison of Three Hybrid Turbulence Models for the Flow Around a Ahmed Body

The flow around the $$25^{\circ }$$25∘ Ahmed body has been studied computationally by applying different methods including an improved URANS formulation, the SAS model and two popular hybrid RANS/LES formulations: DDES and SBES models. All of the turbulence models employ the underlying SST RANS formulation. These hybrid models show a good prediction for the drag coefficient, with an error between 0–4% compared to experiments, whereas the discrepancy is slightly more important for the lift coefficient. The DDES model shows the best representation of the flow features between all the models studied.

F. Delassaux, V. Herbert, I. Mortazavi, C. Ribes

Numerical Simulation of a 3-D Laminar Wing in Transonic Regime

The present paper details the simulations carried out for the 3D-V2C wing configuration designed by Dassault Aviation in the context of the TFAST—Transition location effect on shock boundary layer interaction—European programme. The results concern the constant section wing and the swept one. In the second case, the transition location is imposed by numerical tripping of the eddy-viscosity to examine the impact of its location on the buffet’s onset. The computations have been carried out by using URANS, OES and hybrid approaches. The results analyse the transonic buffet dynamics by means of spectral and POD analysis in case of the constant section wing. They also examine onset of unsteadiness at 5° and 7° of incidence for the swept wing. Because of the chord’s length variation, there are sections where the local Reynolds number is subcritical or supercritical regarding the buffet instability.

D. Szubert, I. Asproulias, N. Simiriotis, Y. Hoarau, M. Braza

Hybrid RANS-LES Study of Transonic Flow in the Wake of a Generic Space Launch Vehicle

Transonic flow in the wake of a generic space launch vehicle is investigated using Improved Delayed Detached-Eddy simulations on quasi-structured, partially unstructured and hybrid grids. It is shown that a $$90^\circ$$90∘ segment of the full domain can already capture the main afterbody flow dynamics and give a good agreement with experimental results. In order to assess the effect of unstructured grids, simulation results on a grid with an unstructured recirculation region are compared to a quasi-structured and a true hybrid grid. Finally, a comparison between IDDES and zonal DES results are presented and discussed.

Tim Horchler, Kai Oßwald, Volker Hannemann, Klaus Hannemann

Detached Eddy Simulation of an SD7003 Airfoil

Laminar separation followed by transition and turbulent reattaching is a key challenge for computational fluid dynamics. Typical RANS models cannot reproduce this behaviour correctly, while LES or DNS only is affordable for quasi two-dimensional configurations. Hybrid RANS-LES models offer a method to reduce the computational effort and resolve larger configurations at reasonable cost. For the present study the simulation of laminar separation on a SD 7003 airfoil has been performed using LES and DDES in order to validate the DDES for this type of application.

Eike Tangermann, Markus Klein

Vortex Breakdown Flows Around a Double-Delta Wing During Pitching Motion Based on DDES

A solver based on rigid moving mesh and DDES techniques is implemented to investigate the unsteady flows around an 80°/65°double delta wing during a sinusoidal pitching motion with reduced frequency equal to 0.4. We focus on the behavior of burst point, helical mode instability, pressure fluctuations and dynamic pitching stability. The response of burst point is nearly a simple harmonic motion and locked in the frequency of pitching motion associated with a phase lag. The time-averaged flow after breakdown regions is still approximately a conical flow, whose cone angle is different from the steady state. Cm lags behind with the variation of incidence, which means dynamic pitching stability is obtained.

Jian Liu, Haisheng Sun, Zhixiang Xiao

On the Convection Velocity of Wall-Bounded Turbulence Resolved by ZDES Mode III at

WMLES simulations of a flat-plate zero-pressure-gradient boundary layer are done with the Zonal Detached Eddy Simulation Mode III technique over a wide range of Reynolds numbers $$3\,150 \le Re_\theta \le 14\,000$$3150≤Reθ≤14000. A WMLES field is compared with the WRLES interpolated onto the WMLES mesh. Two interface heights are considered, $$y_\text {interface} = 0.1 \delta$$yinterface=0.1δ and $$y^+_\text {interface} = 3.9 \sqrt{Re_\tau }$$yinterface+=3.9Reτ. The prediction and resolved fraction of mean skin friction is discussed, as well as remaining issues, especially in the logarithmic layer. An excess of high-wavelength streamwise velocity fluctuations is observed below the RANS/LES interface with $$y^+_\text {interface} = 3.9 \sqrt{Re_\tau }$$yinterface+=3.9Reτ, and studied by a spectral convection velocity analysis, leading to the suggestion that it may be a footprint of coherent structures located further away from the wall.

Nicolas Renard, S. Deck

Hybrid RANS/LES Simulation of a Supersonic Coaxial He/Air Jet Experiment at Various Turbulent Lewis Numbers

In this article, the unstructured, high order finite-volume CFD solver FLUSEPA, developed by Airbus Safran Launchers, is used to simulate a supersonic coaxial Helium/Air mixing experiment. The aim is to assess the ability of the code to accurately represent mixing in compressible flows and to create a reference case in order to test a future hybrid RANS/LES (HRL) model with variable turbulent Prandtl and Schmidt numbers. Both RANS and HRL simulations are performed and the impact of Lewis number on the results is studied. Fine and coarse meshes are used to see the influence of spatial resolution on modeled and resolved scales. General good agreement is obtained for both RANS and HRL simulations. Predictably, the choice of Lewis numbers has almost no impact on the time-averaged fields of the fine HRL simulation. Its role is more significant on the coarse mesh and the steady RANS simulations.

Lorris Charrier, Grégoire Pont, Simon Marié, Pierre Brenner, Francesco Grasso

Hybrid RANS/LES Simulation of a Space Launcher Using a High Order Finite Volume Scheme and Grid Intersections Technique

In this study, we apply a numerical strategy, based on high-accurate finite volume numerical schemes and advanced turbulence models, to calculate the mean and fluctuating pressure in the recirculation zone of a mock up of the Ariane 5 space launcher, which is one of our advanced validation test cases for the FLUSEPA solver, developed by Airbus Safran Launchers.

Grégoire Pont, David Puech, Pierre Brenner

Detached-Eddy Simulation of a Horizontal Axis Wind Turbine

Aerodynamic simulations of a small horizontal-axis wind turbine, suitable for integration of wind energy in urban and peri-urban areas, are performed using the improved delayed detached-eddy simulation method. Simulations are carried out for three rotation rates and inlet conditions. Aerodynamic characteristics of the wind turbine such as forces, power production, pressure distribution as well as flow topologies are presented. The effect of different rotation rates as well as the effect of free stream turbulence on the turbine aerodynamics are discussed.

Amin Rasam, Zeinab Pouransari, Karl Bolin, Ciarán J. O’Reilly

Hybrid RANS/LES Capabilities of the Flow Solver FLOWer—Application to Flow Around Wind Turbines

The compressible block-structured flow solver FLOWer of the German Aerospace Center (DLR) has been extended towards state of the art detached-eddy simulation (DES) methods in order to conduct hybrid RANS/LES simulations of flow around rotary wings. The large-eddy simulation (LES) capabilities of the code are demonstrated for decaying isotropic turbulence. Excessive numerical dissipation is avoided by using the fifth-order WENO scheme and an appropriate low-Mach number correction. The DES implementations are validated first for the well documented test cases backward facing step and NACA0021 airfoil at$$60^\circ$$60∘incidence, before increasing the complexity by simulating the flow around the MEXICO model wind turbine operating in stalled conditions and comparing with experimental data. From the latter, recommendations on the numerical settings are derived to successfully set up eddy resolving simulations for wind turbine or helicopter applications.

Pascal Weihing, Johannes Letzgus, Galih Bangga, Thorsten Lutz, Ewald Krämer

Multi-disciplinary Analysis of Flow in Weapon Bays

Scale-Adaptive Simulations of store release from weapon bays using overset grids are presented in this paper. A six-degree-of-freedom model is coupled with the HMB3 flow solver, and store release simulations are performed for a finned store inside an idealised bay. A wavelets analysis revealed that the tonal noise radiated from the cavity is generated by standing waves. It is also found that the trajectories of stores released from the cavities are affected by the mean flow field, the standing waves, and the dynamics of the shear layer formed along the cavity opening.

Gaëtan J. M. Loupy, George N. Barakos

Parametric Study of Cavity Leading-Edge Rod Spoilers by Advanced Hybrid RANS-LES Methods

Improved delayed detached-eddy simulation is performed to explore the control mechanism of the transverse rod spoiler near the leading-edge of an open-type cavity at Ma = 0.9. The rod induces vertical velocity and lifts up the shear layer, significantly reducing the pressure fluctuation inside the cavity. Rossiter peaks are damped and energy is redistributed to the high frequency components near the cavity leading-edge. Vortex shedding after the rod generates high frequency peaks. Then three rod spoilers of different diameters and gap distances are numerically evaluated and compared. A narrow gap between the rod and the wall tends to weaken the lifting-up of the shear layer. Large rod diameter enhances the lifting-up, but also generates excessive perturbation, which is also the case for the gap distance.

Kunyu Luo, Zhixiang Xiao, Zhe Weng, Ning Zong, Lidong Deng

Hybrid RANS-LES Turbulence Modelling in Aeroelastic Problems, Test Case 3 from the Second AIAA Aeroelastic Prediction Workshop

Prediction of the dynamic response of aircraft in the entire flight envelope is necessary in order to define stability margins in any possible operative situation, in particular where the flow is strongly affected by compressibility and viscous effects. Complex flow phenomena appear such as shock induced boundary layer separations, characterized by multiple turbulent time and lenghtscales. Aeroelasticists traditionally prefer the URANS approach; however, hybrid RANS-LES simulations are increasingly popular, at least among researchers. The Second AIAA Aeroelastic Prediction Workshop has proposed a test case, Test Case 3, where the flow physics may benefit from the higher physical consistence of RANS-LES modelling. A number of considerations, prompted by the discussions with the organizers and participants, are proposed.

M. Righi

Improvement of CFD-Wind Tunnel Correlation Near Buffet Onset by Using Scale Resolving Simulations

This paper is dedicated to the assessment of turbulence modeling for the aerodynamic study in transonic conditions of a long-haul business jet with a narrow fuselage, slender backswept high aspect ratio wings with fuselage mounted engines. The model of this aircraft was tested in the DNW-HST, one of the pressurized transonic facilities of the German-Dutch Wind tunnels. The CFD results were obtained using the following model: RANS Menter SST k-ω, which is the reference model, Unsteady-RANS (URANS) Menter SST k-ω and Hybrid RANS-LES (HRL) models based on the same SST model. The used hybrid RANS-LES models are: the SAS (Scale Adaptive Simulation) and the SBES model (Stress-Blended Eddy Simulation) based on the WALE model. Another feature that was investigated was the influence of the use of upwind-central reconstruction blending and the use of a dedicated laminar-turbulent transition model. A special attention was paid to properly capture the aerodynamic coefficients at angle-of-attack of 5.5°, corresponding to buffet. The buffet is an unwanted unsteady phenomenon characterized by the interaction of the shock wave and the detached boundary layer formed behind it. The final goal was to find the most economic and robust turbulence model able to capture the aerodynamic coefficients given an acceptable accuracy.

M. G. Cojocaru, M. Zhong, M. L. Niculescu, G. L. Wang, S. Zheng, C. Nae

Numerical Simulations of the Flow Dynamics Past an Oscillating Rod-Airfoil Configuration

The rod-airfoil subjected to a forced oscillation was numerically studied using the Improved Delayed Detached Eddy Simulation (IDDES) method. The freestream flow Mach number is 0.21 and Reynolds number based on the rod diameter is 48000. The transversely oscillating motion of the rod-airfoil changes the flow properties dramatically, compared to the stationary case. The shear layers become unstable earlier and the formation length is shortened, although the oscillating case has less small-scale structures. The oscillation enhances the lift fluctuations sharply and changes the phase relationships of lift between the rod and the airfoil. The relationships between the time history of lift coefficients and the evolutions of instantaneous flow fields are also explored.

Wenqing Zhu, Kunyu Luo, Zhixiang Xiao, Song Fu

Modelled and Resolved Turbulent Stresses Around a Circular Cylinder Using DES

Massively separated flows at high Reynolds numbers over a circular cylinder are simulated numerically using an in-house CFD code called Dynamic Grid Detached Eddy Simulation (DG-DES). Turbulent kinetic energy is approximated using Bradshaw’s hypothesis [2] and normal and shear stresses are computed. Comparison of time averaged normalized velocity and resolved stresses is done with the experimental data [3] at Re = 1.4 × 105. A comparison of the modelled and resolved turbulent stresses is also made at the Re = 8 × 106.The comparison of computed normalized velocity and turbulent Reynolds stresses with the available experimental data shows good results. It shows that the DES method has preserved the flow physics well while switching from RANS to LES mode. It also shows that normal and shear stress computed using the Bradshaw’s approximation to compute kinetic energy gives good results. The comparison of modelled and resolved turbulent stresses shows that the modelled stresses are concentrated in the boundary layer and shear layer region (RANS regions) and the resolved stresses are dominant in the separated flow region (LES region).

Naveed Durrani

Numerical Study of 3D Turbulent Cavitating Flows

A numerical investigation of the behaviour of a 3D cavitation sheet developing along a Venturi geometry has been performed using both a compressible one-fluid RANS solver and a pressure-based solver. The interplay between turbulence and cavitation regarding the unsteadiness and the structure of the flow is complex and not well understood. This constitutes a determinant point to accurately simulate the dynamic of sheet cavities. The mass transfer between phases is driven by a void ratio transport equation model. Turbulence is taken into account using Scale-Adaptive models (SAS). 3D simulations are compared with the experimental data.

E. Goncalves, J. Decaix, B. Charriere

Hybrid LES/RANS Predictions of Flows and Acoustics from an Ultra-High-Bypass-Ratio Serrated Nozzle

In this paper, the jet flow from an industrially relevant ultra-high-bypass-ratio (UHBPR) serrated nozzle has been simulated in a flight stream. The methodology to tackle complex geometries and multi-disciplinary physics is demonstrated in detail and validated using a single stream jet with measurements. A reliable industrial process chain is explored. This type of complex geometry jet simulation shows great potential to replace parts of experimental tests in the near future.

Zhong-Nan Wang, James Tyacke, Paul Tucker

Cross Flow Induced Vibration in a Single Tube of Square Array Using LES

Large eddy simulations (LES) of a single phase water flow through a square normal tube bundle at Reynolds numbers from 2000 to 6000 is performed to investigate the fluid-elastic instability. A single cylinder of the array is allowed to oscillate in one degree of freedom (1-DOF) in the flow normal direction, similar as in the corresponding experiments. The fluid-structure coupling is simulated using the Arbitrary Lagrangian-Eulerian (ALE) approach. The subgrid scale turbulence is modeled using the standard Smagorinsky’s eddy-viscosity model. The LES results show a good agreement with the experimental results, in terms of the response frequency and damping ratio of the cylinder vibration. The dynamic case simulations are compared with static cases over the range of Reynolds numbers by means of the pressure profiles on the cylinder surface and the probe velocity spectra.

Vilas Shinde, Elisabeth Longatte, Franck Baj, Y. Hoarau, M. Braza

Experimental and Numerical Investigation of a Heated Impinging Jet for a Small Nozzle-to-Plate Distance and High Reynolds Number

This paper presents a comprehensive study of an impinging jet configuration (Grenson et al, Int J Heat Mass Trans 102:801–815, 2016), which has been selected for its high Reynolds number ReD = 60,000, small nozzle-to-plate distance H/D = 3 and temperature difference between the heated jet and the ambient. First, the experiments are described and analysed, then numerical simulations (DNS, LES, ZDES and RANS) are assessed to evaluate the resolution level required to capture the salient features of this configuration.

F. Gand, P. Grenson, I. Mary, H. Deniau, P. Reulet, B. Aupoix

An Algebraic Hybrid RANS-LES Model with Application to Turbulent Heat Transfer

An algebraic hybrid RANS-LES model is proposed. The RANS mode employs a modified mixing-length approach near walls. Instead of using the magnitude of the resolved strain-rate tensor, the advanced spatial operator used by the WALE subgrid-scale model is embedded into the formulation due to its better scaling properties for the turbulent/eddy-viscosity. The LES mode incorporates the well-known WALE model to resolve flow in the rest of the domain. Similar to the robust, well-calibrated, low-cost, algebraic hybrid RANS-LES model (HYB0) which combines simple mixing length-type RANS near wall with Smagorinsky model in the off-wall region, the same turbulent length-scale adaptation approach for the RANS-LES interface is utilized for proper interaction between the modes. In addition to correct near-wall behaviour, the use of the advanced WALE differential operator should theoretically ensure smooth transition at the interface, detection of turbulent structures inside the eddies and better prediction of the log-layer velocity profile. Turbulent Rayleigh-Bénard problem is studied using both models to examine and to compare their performances without the Boussinesq approximation. It is found that HYB0 is slightly dissipative compared to mHYB0 and predicts fewer interactions among thermal plumes. However, HYB0 has interestingly better near-wall behavior. No interface issues are observed with the usage of the WALE operator. Further applications are required to characterize the behavior of the both models.

Ilyas Yilmaz

Comparison of Hybrid RANS-LES Simulations of Turbulent Flow and Heat Transfer in a Ribbed Duct

Numerical predictions of the turbulent flow and heat transfer of a stationary duct with square ribs 45° angled to the main flow direction are presented. The rib height to channel hydraulic diameter is 0.1, the rib pitch to rib height is 10. The calculations have been carried out for a bulk Reynolds number of 50,000. The flows generated by ribs are dominated by separating and reattaching shear layers with vortex shedding and secondary flows in the cross-section. The one of hybrid RANS-LES approaches, Detached Eddy Simulation (DES), is adopted to simulate such flows at a reasonable computation cost. The capability of the various versions of DES method, depending on the RANS model, such as Spalart-Allmaras model (SA), Realizable k-ε model (RKE) and Shear Stress Transport (SST) model, has been compared and evaluated against the experimental data. The significant effect of RANS model on the accuracy of the DES prediction has been shown. The DES-SST method, which was able to reproduce the reasonable physics of flow and heat transfer in a ribbed duct, showed better performance than others.

Sung in Kim, Aidan O’Sullivan