Fluid Mechanics and Fluid Power, Volume 7

Given the imminent depletion of fossil fuels, the present scenario relies on capturing solar energy. The current study compares experimental trials of traditional SAH with alternative impinging jet ribbed solar air heater designs. The experimental investigation is investigated by increasing the Re from 4000 to 16,500 and comparing the results. The geometric parameters and jet parameters used in the investigation were e/d_hd = 0.043, P/e = 10, α = 55°, X_st/d_hd = 0.40, Y_sp/d_hd = 0.84, and d_j/d_hd = 0.064. The impinging jet with multi-V-shaped ribs outperformed the V-shaped ribbed SAH, with a reported thermohydraulic efficiency of 3.301 compared to 2.05 for the V-shaped ribbed SAH and 1.83 for the impinging jet flat-plate solar air. It establishes that when active and passive heat transfer approaches are coupled, heat transfer enhancement and THEP are increased. The findings were also compared to traditional SAH.

A solar air heater is easy to build and easy to use for drying applications, room heating purposes, etc. In the present study, single-pass forced convection rectangular-type solar air heater is studied numerically. The copper metal foam with 0.92 porosity is used for case (a) empty channel, cases (b) to (e) comprising of different stepped-type arrangements, and case (f) fully filled metal foam condition and studied numerically to obtain outlet temperature, pressure drop and the performance factor of the solar air heater. The Reynolds number is varied from 4401 to 5868. Based on this range of Reynolds number RNG k-ε model with enhanced wall function is adopted for numerical simulations. The local thermal equilibrium model is used to simulate the porous zone. The Rosseland radiation model has been chosen with solar ray tracing method. The case (c) is the best stepped-type arrangement to get same outlet temperature compared to fully filled metal foam case (f). Hence, the material cost is minimized. The temperature rise is 8.89% more compared to empty channel solar air heater. Case (c) has less pressure drop compared to other metal foam arrangements. The performance factor for case (c) is 2.03.

In this research work, experiments are conducted in a U-type evacuated tube solar collector (ETSC), which can be used for producing medium-temperature industrial process hot air. The amount of heat gain, thermal performance, and efficiency of the U-type ETSC with air as the working fluid are studied experimentally. Solar radiation is found as the main important parameter for the efficiency and higher collector outlet temperatures. The values of the highest collector efficiencies are observed between 1:30 PM and 2 PM due to higher solar radiation at this time. The energetic and exergetic efficiencies of the collector are determined, and the results are presented in this paper. From the experimental results, it can be concluded that the developed U-type with ETSC can be useful for medium-temperature industrial process heating applications.

Wake characteristics of wind turbines such as wake width, velocity deficit, and turbulence intensity are important factors for optimal placement of wind turbine rotors in an array in a typical wind farm. Reduced-order analytical wake models are useful tools in wind-farm layout design due to their simplicity and low computational demand. However, the suitability of such reduced-order models has to be tested with more refined CFD studies before they can be deployed in the optimization of wind-farm layout. In this study, a detailed comparison of widely used analytical wake models with CFD studies on static and dynamic Savonius Vertical Axis Wind Turbine (S-VAWT) is done. The CFD studies involve solving the Reynolds-averaged Navier–Stokes (RANS) equations using finite volume method-based Ansys Fluent. The comparative investigation showed that the analytical wake models reported in the literature are capable of predicting wake characteristics such as the wake width; however, they fail to predict the wake velocity deficit. Moreover, the asymmetry in the wake velocity profile, which is a characteristic feature of S-VAWTs, is not captured by the models. This highlights the need for developing new analytical wake models that are better suited for S-VAWTs.

The world is witnessing the transformation of countries toward the adoption of renewable sources for power generation. Power generation through solar photovoltaic is at the top preference due to its proven advantages. Among the various technology in solar PV, floating solar photovoltaic is emerging in the past decade as it shows higher performance than ground-mounted PV system, reduces CO₂ emission, saves land, and saves water from evaporation. In this view, the research that has been conducted across the world in the year 2022 and reported in various publications has been discussed in this article. The review presents the reported software used for the geographical and meteorological data collection, performance analysis, thermal analysis, FSPV in hydro-reservoirs, environmental effects, and FSPV in marine condition are discussed. Based on the investigation, it is proved that the floating solar photovoltaic is a robust source of energy that has a huge demand in the global market as it can replace the non-renewable sources for power generation.

The present research work proposes a method to optimize the geometrical parameters of a large-scale heliostat reflector using CFD analysis. The use of heliostat reflectors in solar cookers is well established because of its low-cost production. Determining the best configuration of a fixed shape of inverted frustum of a square pyramid reflector is very helpful as it can avoid the tracking of reflector. The reflector height and dimensions of sides of the top surface are kept constant which are 1.75 and 5 × 5 m², respectively. Results are obtained by varying the dimensions of the bottom sides of the reflector by 5%. All 32 combinations are tested for a time interval of 15 min considering daily radiation data for the time period starting from 0900 to 1700 h. To analyze the effect of these varying parameters, total daily radiation heat flux at the top and base is calculated, and a dimensionless concentration factor is calculated to get the topology optimization. Two dimensionless parameters are identified, viz., height-to-base ratio and area ratio of top to bottom surface, the values of which are 0.7 and 2. These dimensionless geometrical parameters can be utilized to manufacture heliostat solar reflectors.

The objective of the present work is to assess the performance of a pitch type WEC suited for a potential location along the Indian coastline through CFD simulations of multiphase flows. A numerical wave tank (NWT) is modelled and validated with and without the presence of the WEC-rotor, with the waves being generated by the inlet velocity using Stokes second-order wave theory. Based on the hydrodynamic performance assessment carried out, the power absorption capacity and hydrodynamic efficacy of the WEC- rotor are estimated for a range of sea-states.

Global energy demand has increased due to population expansion and improved living conditions. PV/T systems have lately gained popularity as a means of fulfilling this energy demand. The current study examines the effect of CuO/EG nanofluid on the performance of a flat-plate solar collector. An experimental investigation of the thermal rheological properties of CuO/EG nanofluid is carried out. TEM and XRD are used to determine the size and crystallinity of the particles. Stable nanofluids with a volume percentage of 1% are synthesised without the use of any surfactant. Experimental results show an increase of about 20% in thermal conductivity with a subsequent increase of 42% in viscosity. Furthermore, a numerical simulation is carried out for a flat-plate hybrid PV/T solar collector in a laminar flow regime with Re values ranging from 100 to 500. The effect of nanoparticle concentration on heat transfer is established by calculating the increase in heat transfer coefficient. Consequently, the effect of nanoparticle concentration on pressure drop is calculated to estimate the increase in pumping power. A comprehensive analysis is done by calculating the thermohydraulic efficiency of the fluid. As concentration increases from 0 to 1 vol%, the overall Nusselt number increases by 21% at Re = 100 and by 200% at Re = 500. Furthermore, as concentration increases from 0% to 1 vol%, the overall pressure drop increases by 75% at Re = 100 and by 210% at Re = 500. A maximum increase of 41.2% in thermohydraulic efficiency is achieved at Re = 500 and 1 vol%.

In this report, we perform a numerical analysis of a three-dimensional solar air heater (SAH) having a finned absorber plate. The number of fins of circular cross-section (h = 5 mm to h = 25 mm) has been varied from 10 to 25. Finite volume method is adopted to solve the problem numerically. Fluid flow considered in the turbulence regime where Reynolds varies from 4000 to 16,000. Continuity, momentum, and energy equations with k-ε RNG turbulence model are solved to obtain the velocity and temperature field. Brief results of heat transfer are explained with the aid of graphical plots and contours. A uniform heat flux of 1000 W/m² is applied over the absorber plate. It is observed that the performance of the solar air heater mainly depends on Reynolds number, fin height, and relative coarseness of fins. It is found that the average absorber surface temperature at ten fins is 339.92 K and at 335.5944 K at 15 fins, which is the least among all cases. When the number of fins increases beyond 15, the absorber temperature starts rising and becomes 337.737 K at 25 fins. Thus, 15 fins on the absorber plate are the optimum configuration for maximum heat transfer.

A two-dimensional numerical model of the compound parabolic collector (CPC) with a tubular receiver has been developed to study the effect of the concentration ratio of the collector on the flow profile in a horizontally held cavity and heat losses by the collector. Six concentration ratio (CR) values have been analyzed for three diameters. As per the literature, very few studies have investigated this effect for a horizontal CPC cavity. The convective and radiative heat losses have been modeled using the k-epsilon turbulence and surface-to-surface (S2S) radiation models. The heat conduction in walls is considered by giving suitable wall thickness. Different cases have been simulated to obtain total heat losses, Rayleigh number, velocity vectors, and temperature contours. The results showed total heat losses, and the Rayleigh number increased with the concentration ratio. A symmetric bicellular flow pattern was obtained in the CPC cavity for four CR values (1.1, 1.4, 2.9, and 3.9). However, CR values of 2.0 and 2.5 showed a deviation from this behavior by showing an asymmetric behavior for the flow pattern for the same boundary conditions.

Vortex bladeless turbine is a non-conventional turbine that does not use any rotor blades to capture energy from flowing fluid. The device captures the energy of periodic vortices shed downstream of a bluff body, an aero- hydrodynamic effect that has plagued structural engineers and architects for ages in different engineering designs. As the wind passes a fixed structure, the Von Karman vortex sheet-type vortices generate alternate lift forces on the mast (movable structure) and make it start oscillating. Research has shown that such bladeless turbines have an excellent ability to harvest low-speed wind or hydro-energy. Innovative modifications of the mast’s outer surface open the possibility of extracting energy from a flowing stream. In this paper, a new mast system is designed, developed, and experimented with in an open airflow system, which results in a nearly fivefold increase in the amplitude of the vibrations due to vortices. Wake-Induced Vibration (WIV) is also tested in another set of experiments which does not show the same possibilities.

Solar energy is one of the most important renewable energies utilized in numerous applications. The present work focuses on numerical analysis of a solar air heater (SAH). The main challenge in SAH is to improve the temperature of the air keeping the absorber plate temperature within the limiting range. It can be achieved with the addition of fins or baffles at the cost of pressure loss. In the present work, the effect of conducting baffles on the thermos-hydraulic performance of SAH is studied. A constant heat flux (1110 W/m²) is applied on the absorber plate. Average Nu and the frictional pressure drop across the solar air heater are comprehensively investigated using the commercial software of Ansys Fluent. The baffle height and number of baffles are varied in the range of 0 to 0.03 m and 0 to 33. The air flow in SAH is considered in turbulence range with Reynolds number varying from 4000 to 16,000. It is observed that Nu becomes maximum at nine baffles at a baffle width and height of 0.06 and 0.02 m for both Re of 8000 and 16,000. The pressure drop follows the same trend of Nu and becomes maximum at nine baffles.

Performance improvements on wind turbines are emerging due to increased renewable energy demand. The researchers are focusing on improvements in turbine efficiencies. The advancements in numerical simulations immensely support the new design developments and deployment of wind turbines. However, the fidelity and shortcomings of various numerical models are highly challenging to predict accurate results. One of the challenges in numerical simulations is the stopping criteria for the simulations after specific turbine rotations for highly accurate predictions. This paper investigates the influence of turbine rotations on the numerical prediction accuracy for a standalone three-bladed NACA0021 vertical axis wind turbine. The SST k-\(\omega \) turbulence model is used in 2D turbine configurations. A comprehensive turbine revolution study is carried out for an extensive range of tip speed ratio (TSR) values. The simulation result shows that the operating TSR highly influences prediction accuracy. For lower TSR, a minimal number of turbine rotations are required as compared to higher TSR.

Savonius vertical axis wind turbines (VAWT) are very common off-grid power producing devices. The ideal environment for its operation is undisturbed freestream wind which is rarely available in urban surroundings. Operational environment has a significant effect on the performance of VAWT related to power production. The last decade has served as a transition period in the transport industry, from fossil fuel-based to electric-based vehicles. Regenerative braking and other methods are already in place to produce electricity onboard. This work aims to produce power onboard using a VAWT in the air vents of cars by utilizing the air intake space. A 2D computational study was conducted on an open-source tool OpenFOAM to showcase the potential of power production, when the turbine is kept between the blocks representing the car body and when the turbine is in the free stream velocity. A wind velocity of 5, 7, and 9 m/s was adopted to compare both the models with Re. no. 12804, 17,925, and 23,047. The performance for the turbine between blocks performs better in terms of coefficient of torque and C_P values.

The primary drawback of the solar air heater (SAH) is a decreased heat transfer coefficient caused by the development of a laminar sublayer on the absorber plate's surface. This laminar sublayer can be eliminated by various methods. One of the methods is to use artificial roughened absorber plate. Artificial roughness will improve the heat transfer coefficient, but it also increases the pressure drop; therefore, the ribs must be provided in such a way that solar air heater's overall thermo-hydraulic performance is enhanced. In the current study, SAH analysis was carried out with smooth and artificially roughened absorber plate in the form of NACA 0040 profile ribs with V-down orientation with an angle of attack of 45° in the reverse manner. Experimental results were used to validate the numerically generated results in the Reynolds number (Re) range of 6000 to 18,000. The values of relative roughness pitch and relative roughness height were kept as 5 and 0.065 respectively. As compared to a smooth absorber plate, the ribs’ provision improved the Nusselt number and friction factor by 37.51–59.42 and 19.89–26.22% respectively. The maximum thermo-hydraulic performance parameter (THPP) was found to be 1.48 at Re of 16,000.

Single-camera micro-PIV and PTV measurements were performed in diverging-converging micro-channel to study the suspension flow. In micro-channel, the width of the left and right daughter branch constant at 200 µm. A small quantity of 1 µm dyed particles was mixed with the suspension to measure background fluid velocity with the micro-particle image velocimetry technique (μ-PIV), and a small quantity of dispersed particle (6 μm or 10 μm) dyed to measure particle-phase velocity profile and particle distribution using micro-particle tracking velocimetry (μ-PTV). A tip-valley-tip velocity profile was observed near the divergence, which gradually reduces to blunted profile at the outlet of the confluence section. We have qualitatively studied the concentration by using in-house developed particle counting MATLAB programme and from micro-PTV vector map. At the inlet locations of diverging section concentration profile was symmetric due to particle migration towards the centre of the channel which becomes asymmetric at the daughter branches. The profile becomes again symmetric due to additional particles migration towards the centre of daughter branches and in the outlet locations of converging sections.

An endeavor is made to design the intrusive emission measurement technique to predict the combustion reaction with a precise species concentration. The present study built two (P1 and P2) different orifice diameters of gas sampling probes with a water-cooled system. A laminar premixed CH₄/Air one-dimensional flame is chosen for the product concentration measurements. The flame area contraction ratio using direct images demonstrates probe-induced flame interference. The probe configuration is evaluated based on thermo-physical properties and emission measurement. The sampling velocity, quenching temperature, and residence time emphasize the understanding of aerodynamic quenching in the designed probe. The sampled gas temperature is observed to be well below the quenching temperature limit within a chemical time scale. The smaller orifice diameter of the probe, in this case, P2, is most likely to measure species concentration accurately. In addition, a higher sampling velocity and lower flame stretching can be expected. The gas sampling probe measured CO₂ concentration corroborates with the numerical solution.

The present study aims to characterize the free stream flow of the newly installed recirculating water tunnel facility in the BIAHR Laboratory at the Indian Institute of Technology Kharagpur. This tunnel can operate at speeds ranging from 0.05 m/s to 0.40 m/s in the test section. The dimension of the test section is 400 × 400 × 1500 mm³ in width, depth, and length respectively. An acoustic Doppler velocimetry is used to measure the instantaneous velocity in the test section at the frequency of 10 Hz with a measured accuracy of ± 1%. The flow velocity in the test section is found to vary linearly with motor speed, and the turbulence level decreases on increasing the motor speed. The average temporal stability in the tunnel is found to be less than 1%, and the maximum possible deviation in the spatial uniformity is less than ± 1.35%. Furthermore, the free stream turbulence intensity characteristics in the test section are determined at different operating velocities.

We have performed an experimental flow visualization for a flow over an axisymmetric body which has a spherical shape. To explain the flow visualization images, we have also carried out the global stability analysis. The aspect ratio (χ) of the spherical shape body is defined as χ = 2W/D, where W and D are the width and the base diameter, respectively. We present here some flow visualization and stability calculations for χ = 0.6. We used Laser-Induced Florescence (LIF) technique for flow visualization. The flow speed has been set such that the Strouhal number is found to be 0.12, which is similar to the vortex shedding frequency of a sphere. The wake structure is compared with the global Eigen modes obtained from the stability analysis.

A 3D Acoustic Doppler velocimeter was used in the current investigation to quantify the mean and turbulence characteristics in non-uniform open-channel flows. Results are obtained from studies done in laboratory, analysing the behaviour of sand particles under turbulent open-channel flow conditions flowing through rough, porous beds. Data obtained from ADV is used to calculate turbulent flow characteristics, Reynolds stresses and turbulent kinetic energy. Theoretical formulations for the distribution of Reynolds stress and the vertical velocity have been constructed using the Reynolds equation and the continuity equation of 2D open-channel flow. Measured Reynolds stress profile and the vertical velocity are comparable with the derived expressions. This study uses the Navier–Stokes equations for analysing the behaviour of the vertical velocity profile in the dominant region of full-fledged turbulent flows in open channels, and it gives a new origination of the profile. For both wide and narrow open channels, this origination can estimate the time-averaged primary velocity in the turbulent boundary layer's outer region.

Bio-inspired aerodynamics has amazed the scientific community for decades now. It has inspired researchers and innovators to identify solutions to several fundamental and advanced problems in academia and industry. Insight into temporally evolving vortical structures developing in the near field of a beating wing will be helpful to interpret better the aerodynamic forces generated by the flap cycle of an insect. In the present study, high-speed Schlieren imaging is implemented to capture vortex structures on the wings of Pantala flavescens in the tethered arrangement. The method discussed here helps identify various vortical structures like leading edge vortex and trailing edge vortex. A physics-based optical flow method is also implemented to quantify the flow field and interpret the jump in the nature of vorticity during wing rotation at the end of the stroke. It is also demonstrated that this method has the potential to capture the vortex structure. The present study illustrates how this method is not limited to presenting flow visualization or qualitatively complementing the force measurement tests but also has the potential to provide a quantified velocity field.

The present study aims to measure the volumetric flow field of a circular synthetic jet using three-dimensional particle tracking velocimetry (3D-PTV). The statistical flow characteristics of the synthetic jet have been discussed using ensemble-averaged velocities and their fluctuations. The 3D-PTV data is compared with the 2D-PIV data for the same formation number. The jet width is different in both cases, which owes to the difference in the orifice configuration in the two measurement cases. The streamwise velocity and root mean square velocity dominates the flow owing to the induced velocity of the vortex rings. The transverse velocity and its fluctuations are more than the vertical velocity and its fluctuation. The time evolution of the circular vortex ring has also been shown for two actuation cycles using isosurfaces plots of the normalized vorticity magnitude, which infers that the induced velocity of the vortex ring remains nearly the same throughout the flow field. The streamwise turbulence decreases along the downstream direction, but the ring loses its coherence in the far field due to persisting vertical and transverse turbulence.

The iron and steel industry produces a waste product called slag. The Dry Spinning Disc Granulation (DSDG) process has been experimentally tried, widely, for the granulation of Blast Furnace (BF) slag with the recovery of heat from the high temperature slag. To study this phenomenon, the fabrication of an experimental setup, of the scale of laboratory level, has been done in the institute of the authors. Various experiments were performed on the setup. Stage-wise modifications were performed on the experimental setup on the basis of the limitations found in the previous stages of the experimental setup. In this paper, the methodology, that was adopted to perform the experiments in literature has been studied. Further, the methodology chosen for the current experimental setup has been discussed with each system, its subsystem, and the respective components. Finally, the chosen methodology for the current experimental setup has been compared with the methodologies of the experimental setups stated in the literature. The use of the current experiment methodology has been satisfactorily justified with reference to the literature surveyed. The Air Flow System (AFS) is a novel system that has been used in the current experimental setup of Spinning Disc Atomization (SDA).

Flow past a stationary circular cylinder is studied experimentally in an inclined flowing soap film. Experiments are conducted in the low Reynolds number regime (Re < 200). Images acquired using a high-speed camera are used to study the global wake structure of the circular cylinder for different Reynolds numbers. Both the near-wake and the far-wake are closely observed for the variation of wake characteristics such as recirculation bubble length, shedding frequency of the vortices, and the intervortex spacing of von Karman vortex street with the soap solution's volumetric flow rate. As the flow rate rises, the wavelength of the vortices first increases, reaches a maximum, and then decreases. The ‘b/a’ ratio (the ratio of the distance between clockwise and counterclockwise vortices to the distance between two successive vortices in the same row) remains constant for large parts of the flow regime studied.

We study impact of water-glycerol droplets on a flexible surface, in particular the effect of viscosity on the overall system’s dynamics. We experimentally analyzed the impact dynamics and cantilever response of the system. A thin hydrophilic cantilever beam, made of copper, was used as a flexible substrate. During impact, the viscosity of a droplet damps the substrate’s vibration by dissipating the system’s energy. However, we observed that the initial dynamics of the droplet also contribute to the damping of the cantilever. An analytical model was presented to predict the motion of a cantilever beam, which was shown to be in good accord with our experimental findings.

Accurate knowledge of avalanche impact pressure is vital for the design of avalanche control middle-zone and run-out zone structures. Very little database is available in this regard. With the motivation to fill the knowledge gaps in this area and to develop comprehensive database towards improved guidelines for the avalanche impact pressures on the avalanche control structures, an instrumented structure of size 1.0 m height and 0.65 m width has been developed and installed on a 61 m long experimental facility snow chute located at Field Research Station, Dhundhi (near Manali, Himachal Pradesh), India, for avalanche impact pressure measurement. Four equally spaced piezoelectric force sensors are fitted in the centre of the structure. The measured data has been analysed and compared with the theoretically estimated avalanche impact pressures acquired using the Voellmy–Salm model, and both are found in reasonably good agreement with each other. The obtained results portray that the maximum avalanche impact pressure varies in the range of approximately 15–40 kPa, and the present theoretical predictions are accurate within 20.4% with respect to the experimental observations.

The iron and steel industry produces a waste product, slag. Dry Spinning Disc Granulation (DSDG) process has been experimentally tried, widely, for the granulation of Blast Furnace (BF) slag, with the recovery of heat from the high temperature slag. To study this phenomenon, the fabrication of an experimental setup, of the scale of laboratory level, has been done in the institute of the authors. Various experiments were performed on the setup. Stage-wise modifications were performed on the experimental setup, on the basis of the limitations found in the previous stages of the experimental setup. In this study, the experimental setup with all its systems has been elaborated. Then, after the setup is acquainted, a study has been performed to find the effect of change in disc rotation direction with air blast on liquid flow characteristics. Finally, the results have been discussed and the conclusions drawn.