CFD Study Research Articles

Wind tunnel testing of a Formula Student vehicle for checking CFD simulation trends

The aerodynamic performance analysis of Formula Student racecars has been mostly done by teams with CFD tools, for time and cost savings, that often lack proper validation. To address this, the FST Lisboa team performed a detailed wind tunnel (WT) test campaign, using a one-third scale model, under different configurations, including variable ride heights, bullhorn appendix, and rear wing flap settings, also replicated in CFD. The simulations used RANS with the SST k-omega turbulence model, with a 13.7 million polyhedral mesh for the test chamber region domain. Both experimental and numerical errors were estimated from the instrumentation and mesh convergence analysis, respectively. Comparisons were made between WT and CFD both in terms of local flow, using tufts for flow visualization, and global flow, using lift, drag, and pitching moment coefficients. Overall, the numerical streamlines agreed very well with the orientations of the tufts in experiments, but some discrepancies were found in regions of cross-flow and high-frequency unsteadiness, mainly caused by limitations of the visualization technique. The gamma transition model in CFD was abandoned as it could not replicate the WT observations. In terms of aerodynamic coefficients, a strong correlation was found between WT and CFD. The parametric studies revealed that the simulations captured the experimental sensitivity to each car setting parameter studied but the uncertainties did not enable a full quantitative evaluation of the aerodynamic performance. The drag reduction system significantly impacted the aerodynamic balance of the racecar, while the current bullhorn design proved to be ineffective. The ride height increase led to higher downforce, mostly due to the higher pitch angle of the vehicle, with negligible variation of the aerodynamic balance. This work validated the team CFD studies, building confidence in that trends estimated in numerical parametric studies are likely to be translated to the real prototype performance.

A CFD study of the gas reaction path in growth of InN films in metal–organic chemical vapor deposition

During simulation of the growth of indium nitride (InN) thin films in metal–organic chemical vapor deposition (MOCVD), different choices of kinetic parameters (activation energy Ea and pre-exponential factor A) for gas-phase reactions give rise to many uncertainties in the gas reaction path and growth rate. This study summarized and compared the kinetic parameters of gas-phase reactions during InN MOCVD growth. The InN MOCVD growth in a close-coupled showerhead reactor was simulated with varying kinetic parameters of gas-phase reactions. The effects of kinetic parameters on the gas reaction path were determined by comparing molar concentrations and growth rates of primary In-containing substances. The results show that with varying kinetic parameters, the gas reaction path is likely to be dominated by the addition or trimethylindium pyrolysis path, or to proceed through both reaction paths. Although the reaction path changes with varying kinetic parameters, the predicted growth rates do not vary substantially, because the total rate of transport of In-containing substances to the substrate changes little with the reaction path. The results also indicate that the contribution of pyrolytic products to the growth rate is greater than that of amine, whereas H radicals have minimal effect on the gas reaction path in InN MOCVD growth.

Investigations into the Effect of Mixing on Steam–Water Two-Phase Subsonic Cross-Flow Stability

Theoretical and experimental aspects of the project were conducted to investigate the effect of the mixing of a swirling steam jet into cross-flowing water. It was observed that based on the theoretical adiabatic estimations for the equilibrium temperature of steam–water mixing and by varying Psteam = 1–3 bar, Pwater = 1 bar and RPM = 60–300 around 97% (experimentally compared to the area it has at initial condition) and 85% (CFD study compared to the area it has at initial condition), an increase in the area under the influence of perfect adiabatic mixing was found. A virtual cover over the steam duct was seen. The area of this virtual cover based on the void fraction of swirling steam had a weak relationship with the total area of the region, inhibiting the perfect mixing for which an analytical relationship had been developed. The effect of mixing on the stability of swirling steam–water cross-flows was overall more than twice that of the effect on the area under the influence of the stability profile protrusions. Thus, an overall rise in inlet pressure contributed to improper mixing, whereas a rise in the RPM contributed to proper mixing inside a fixed window of observations. The effect of spatial scaling of a swirling steam trajectory on mixing in cross-flowing water was also investigated across the vertical plane. Also, the scaling of the vertical trajectories of the swirling steam jets under all operating conditions resulted in merging the regions of perfect mixing to some extent. Thus, the area under the influence of perfect mixing was reduced to around 3–4.7% under all operating conditions with scaling. This type of scaling has enormous potential for the characterization of larger fluid domains in environmental and process engineering studies.

Numerical investigation of the hydrothermal performance of novel vortex generators in a rectangular channel by employing inclination and rotational angles

Vortex generators are passive methods of heat transfer enhancement in any thermal system. However, more research is needed to compare the effects of vortex generators having unique shapes on the flow distribution for high heat transmission. Also, a research gap exists in analyzing how different angular orientations of the vortex generator (VG) affect thermohydraulic performance. Therefore, this CFD study aims to propose a total of five novel vortex generator shapes applying modification on a rectangular VG shape, analyzing and comparing the heat transfer and pressure drop properties in a rectangular channel for the Reynolds number varying in the range of Re=4000–11,000. VG-1 (vortex generator-1) with three triangles on its top side, VG-2 with concave shape arc, VG-3 combined with a rectangle and a triangle, VG-4 consists of a rectangle and two triangles at two corners, while VG-5 consists of a rectangle with a triangular inside cut. Among the five designs, VG-1 gives the most optimal hydrothermal performance, incrementing Nusselt number and friction factor of about 38.2 % and 80.38 %, respectively. Combining these two dimensionless parameters, we get the maximum thermal performance factor, TPF, for VG-1, whereas VG-2 performs the least in terms of TPF. Moreover, compared with conventional rectangular VG, VG-1 performed the best with a 1.63 % increase in TPF. Considering the effect of different angular orientations, VG-1 was further studied by applying five vertical inclination angles and four horizontal rotation angle configurations to investigate the impact of inclination and rotational angles. Minimizing the pressure drop penalty, the 30˚ inclination design had the best hydrothermal performance overall, with the highest TPF range of 1.19–1.41, whereas 120˚ variants had the lowest TPF, at 1.09–1.31. Also, for the configuration of the horizontal rotations, 30˚ angle gives the best result, having a slight edge over 150˚case with 1.17–1.41 TPF. Finally, the best cases from vertical inclination and horizontal rotation are combined in a new hybrid configuration, which yielded the maximum TPF of 1.22–1.45, indicating that this configuration is the most effective among all the cases.

A multi-physics CFD study to investigate the impact of laser beam shaping on metal mixing and molten pool dynamics during laser welding of copper to steel for battery terminal-to-casing connections

This study aims to investigate the impact of laser beam shaping on metal mixing and molten pool dynamics during laser beam welding of Cu-to-steel for battery terminal-to-casing connections. Four beam shapes were tested during LBW of 300 µm Cu to 300 µm nickel-plated steel. Both experiments and simulations were used to study the underlying physics. A CFD model was firstly calibrated against experiments and then deployed to explore the effect of the increasing ring-to-core diameter, as well as a tandem laser spot configuration. The study showed that metal mixing is influenced by the keyhole dynamics and collapse events, but also there is an intricate interplay between keyhole geometry, fluid dynamics via Marangoni forces and buoyancy forces. Notably, the buoyance forces due to the different densities of steel and Cu, along with the recoil pressure contribute to the upward flow of steel towards Cu, and hence impact meaningfully the material mixing. The study pointed-out that the selection of a custom ring-to-core diameter and ring-to-core power is a decision with a trade-off between the need of stabilising the keyhole dynamics and the need to reduce the mixing. Findings indicated that 350 µm ring and 90 µm core with 30% of ring power (weld configuration C3) resulted in more stable dynamics of the keyhole, with significant reduction of collapse events, and ultimately controlled migration of steel towards Cu. Additionally, the pre-heating approach with the tandem beam only led to local fusion of Cu and no significant improvement in keyhole stability was observed.

CFD study of a horizontal axis wind turbine NREL Phase II

The present work aims to study the aerodynamic characteristics of the NREL phase II (generated only with S809 profile along the span for an untwisted case) rotor that is a horizontal axis downwind wind turbine rotor and which is assumed to stand isolated in the space. The two dimensional steady-incompressible flow Reynolds average NavierStokes equations, are solved by using the commercial CFD package Ansys Fluent. The 2D computations are first performed on S809 airfoil in order to define the most suitable model to be used; the turbulence closure model has been chosen among four possible candidates (standard , Spalart-Allmaras, based on comparison of pressure coefficient for the different configurations with experimental results. Secondly, through a three dimensional study we tried to simulate the experiment for wind speed velocities of 7.2, 10.56, 12.85, 16.3, and 9.18m/s. Results of pressure and torque for considered wind turbine rotor have been directly compared to the available experimental data. The comparisons show that CFD results along with the turbulence model used can predict the span-wise loading of the wind turbine rotor with reasonable agreement. The work presented here is the first stage of project that aims at giving a better understanding of the main influence of the rotational effect on boundary layer separation, and identify the stalled configuration in order to control this latter in future work.

Influence of distributor plate design on mixing characteristics of rice husk biomass in a bubbling fluidized bed gasifier: An experimental and CFD study

This study investigates the mixing characteristics of rice husk biomass in a bubbling fluidized bed gasifier (BFBG) using different distributor plates: perforated, 45° slotted, and hybrid plates. The study explores the fluidization characteristics of a biomass/sand mixture using three distributor plates, observing the maximum difference in initial minimum fluidization velocity (Umf,i) and final minimum fluidization velocity (Umf,f) for perforated plate, indicating axial mixing and segregation, while the 45° slotted plate represents uniform bed expansion and fluidization, and the hybrid plate exhibits an intermediate behavior. Axial and lateral biomass distribution is also studied, and it is found that with the 45° slotted plate the highest axial distribution of rice husk is observed at the lower portion due to lateral and swirling flow whereas perforated plate causes the highest deviation at the lower portion but approaches ideal mixing at the mid and upper sections due to axial dominant flow. The hybrid plate exhibits a blend of axial and lateral flows, resulting in intermediate axial distribution at lower and upper section of gasifier. Radially, the perforated plate has the highest concentration of biomass at maximum height whereas the 45° slotted plate has concentration near the walls, and the hybrid plate has optimal mixing throughout. The hybrid plate also achieves the highest mixing index at all air velocities. Overall, the study provides insights into biomass mixing in BFBGs and highlights the superior performance of the hybrid distributor plate.The CFD study also carried out to complement the experimental results in terms of pressure drop and mixing behavior by employing different distributor plats. Multiphase two fluid model (TFM) with kinetic theory of granular flow has been employed for CFD simulations with the engagement of k-epsilon turbulence model. The simulation results are in good agreement with experimental results in terms of bed pressure drop quantitatively and mixing characteristics of rice husk biomass qualitatively.

Optimizing air distribution in floor and wall burners of an industrial steam cracking firebox: a CFD study

A 3D computational fluid dynamics model for an industrial scale steam cracking firebox is combined with a 1D reactor model for the cracking process within the reactor coil. This framework is validated using industrial tunable diode laser absorption spectroscopy (TDLAS) measurements in a naphtha steam cracking furnace. Industrial O2, H2O, CO and temperature data show good agreement with simulation results at different locations within the firebox. The influence of varying the primary-to-secondary air flow distribution to the floor and wall burners separately is investigated using the validated framework. Altering the primary-to-secondary air flow distribution of the floor burners from 75/25 to 25/75 results in a 66% increase in furnace run length and a 35% decrease in NOx formation. This shift in air ratio ensures a lower rollover height of the flame and a large recirculation zone of the flue gas, spreading the radiative heat flux on the reactor coil more evenly. Altering the primary-to-secondary air flow distribution of the sidewall burners from 50/50 to 100/0 results in a 13% increase in run length and a 30% decrease in NOx formation. More primary air towards the sidewall burners is found to lead to more evenly spread out flames along the wall, resulting in flame interactions between the different burners and a combined flow towards the center of the firebox. These interactions result in a more uniform tube metal temperature profile along the different passes of the coil.

Three-dimensional CFD study of triangular solar air heater duct (TSAHD) with trapezoidal ribs

The current numerical analysis presents the thermo-fluidic performance of a triangular solar air heater duct having trapezoidal ribs on the absorber plate. Roughness variables like Non-dimensional pitch and non-dimensional height are varied from 7.5 to 30 and 0.013 to 0.053, respectively and Reynolds number is kept in the turbulent regime, i.e., Reynolds number = − 18 Trapezoidal-shaped ribs with non-dimensional pitch and non-dimensional height of 10 and 0.05, respectively, at Reynolds number of a maximum enhancement of 126% in heat transfer is attained as compared to the base model. A maximum increase in friction penalty is found 2.79 times over base model as a result of a non-dimensional pitch of 10 and non-dimensional height of 0.053 at a Reynolds number of Within the range of analysis, a highest thermal performance ratio of 1.66 is attained for the non-dimensional pitch of 10 and non-dimensional height of 0.053.

Multi-scale CFD study of multiphase flow in structured sinusoidal corrugated sheets packings

Structured packing is an important equipment and has wide applications in chemical separation process. In this study, the complex hydrodynamics characteristics of structured sinusoidal corrugated sheets packings were investigated by 2D liquid film model and 3D Representative Element Unit model. Volume of Fluid method was employed to investigate the effect of eleven different structures of sinusoidal corrugated sheets packings (i.e. wavelength, amplitude, and corrugated angle) on liquid holdup, wet pressure drop, and interfacial area. In addition, a shape factor was proposed to characterize the effect of flow regime on packing hydrodynamics characteristics and wetting performance. The packing shape factor analysis method proposed in this study could provide a reference for the structural optimization and evaluation of structured packing in the future.

CFD Study of the Non-Linear Physical Phenomena of the TLP of a 15-MW-Class FOWT under Extreme Waves

In this study, a numerical simulation was conducted to investigate the non-linear physical phenomena of a tension leg platform (TLP) of a 15-MW-class floating offshore wind turbine (FOWT). Computational fluid dynamics was employed as the numerical tool, and a deforming mesh technique was used to describe the moving body. To examine the non-linear physical phenomena, an irregular wave was generated with a focus on head sea conditions. The springing and ringing responses were calculated from the numerical simulation results, and the relations between the motions and dynamic tensions of the 15-MW-class FOWT TLP were investigated. From the irregular wave impact simulation, it was found that the springing response via the wave sum frequencies and the ringing response occurred at approximately three times the wave peak frequency. Additionally, whipping simulations were conducted under a focused wave. The results show that the response in pitch resonance frequency was caused by the wave impact. The numerical results of this study could be used as fundamental data for FOWT TLP design.

The Biffis Canal Hydrodynamic System Performance Study of Drag-Dominant Tidal Turbine Using Moment Balancing Method

Drag-dominant tidal turbine energy holds tremendous clean energy potential but faces significant hurdles as unsuitability of the actuator disc model due to the varying swept blockage area, unaccounted bypass flow downstream interaction, and rotor parasitic drag, whereas blade element momentum theory is computably effective for majorly 3-blade lift-dominated aerofoil. This study validates a novel method to find the optimal TSR of any turbine with a cost-effective and user-friendly moment balancing algorithm to support robust tidal energy development. Performance analysis CFD study of Pinwheel and Savonius tidal turbines in a Biffis canal hydrodynamic system was carried out. Thrust and idle moment are analyzed as functions of only inlet fluid velocity and rotational speed, respectively. These relationships were verified through regression analysis, and the turbines’ net moment equations were established based on these parameters. In both simulation models, rotational speed and inlet velocity were proved excellent predictor variables (R2 value ≈ 1) for idle and thrust moments, respectively. The optimal TSR values for Pinwheel and Savonius turbines were 2.537 and 0.671, respectively, within an acceptable error range for experimental validation. The optimal basin efficiency (ηopt, TSR) values for Pinwheel and Savonius in the 12% blockage channel were (29.09%, 4.0) and (25.67%, 2.87), respectively. The trade-off between TSRopt and ηopt is the key instruction concerning electricity generation and environmental impact.

Performance characteristics on up-scaling vacuum membrane distillation modules

Large-scale CFD studies are currently lacking in membrane distillation due to high computational overhead. This study utilizes a validated CFD model for vacuum membrane distillation and reduces the order of the model to enable prototype scale simulations. Different module designs were considered: a baseline flat sheet membrane module, a spacer-filled channel, a wavy channel, and a wavy channel with embedded stiffeners. Different lengths (330 mm, 660 mm, and 990 mm) were studied to simulate lab to prototype upscaling. Large Eddy Simulations were run in the laminar (Re 900) and turbulent (Re 3600) flow regimes. For Re 900, cases with geometric alterations (wavy membrane, spacer-filled channel) locally outperformed the baseline case within the first 330 mm before axial temperature polarization equilibrated the performance between the baseline and altered channels. The improvement in local performance was seen over the whole 990 mm length at Re 3600, culminating in a 35–40 % flux improvement versus the baseline at Re 3600 versus a 0–35 % difference at Re 900. Axial temperature polarization was mitigated using heat injection, showing a 5 % flux drop as length tripled compared to a 20–27 % decline. Higher operational Reynolds numbers should be considered cautiously for increasing pressure drop and violating the liquid entry pressure limit for wetting.

Isolated bubble ascent in a non-Newtonian media inside an infinite bubble column: a CFD study

Isolated bubble ascent in a non-Newtonian media inside an infinite bubble column: a CFD study

CFD study of DNB in a hexagonal sub-assembly using MuSiG model

PurposeSubcooled flow boiling phenomenon is characterized by coolant phase change in the vicinity of the heated wall. Although coolant phase change from liquid to vapour phase significantly enhances the heat transfer coefficient due to latent heat of vaporization, eventually the formed vapor bubbles may coalesce and deteriorate the heat transfer from the heated wall to the liquid phase. Due to the poor heat transfer characteristics of the vapour phase, the heat transfer rate drastically reduces when it reaches a specific value of wall heat flux. Such a threshold value is identified as critical heat flux (CHF), and the phenomenon is known as departure from nucleate boiling (DNB). An accurate prediction of CHF and its location is critical to the safe operation of nuclear reactors. Therefore, the present study aims at the prediction of DNB type CHF in a hexagonal sub-assembly.Design/methodology/approachComputational fluid dynamics (CFD) simulations are performed to predict DNB in a hexagonal sub-assembly. The methodology uses an Eulerian–Eulerian multiphase flow (EEMF) model in conjunction with multiple size group (MuSiG) model. The breakup and coalescence of vapour bubbles are accounted using a population balance approach.FindingsBubble departure diameter parameters in EEMF framework are recalibrated to simulate the near atmospheric pressure conditions. The predictions from the modified correlation for bubble departure diameter are found to be in good agreement against the experimental data. The simulations are further extended to investigate the influence of blockage (b) on DNB type CHF at low operating pressure conditions. Larger size vapour bubbles are observed to move away from the corner sub-channel region due to the presence of blockage. Corner sub-channels were found to be more prone to experience DNB type CHF compared to the interior and edge sub-channels.Practical implicationsAn accurate prediction of CHF and its location is critical to the safe operation of nuclear reactors. Moreover, a wide spectrum of heat transfer equipment of engineering interest will be benefited by an accurate prediction of wall characteristics using breakup and coalescence-based models as described in the present study.Originality/valueSimulations are performed to predict DNB type CHF. The EEMF and wall heat flux partition model framework coupled with the MuSiG model is novel, and a detailed variation of the coolant velocity, temperature and vapour volume fraction in a hexagonal sub-assembly was obtained. The present CFD model framework was observed to predict the onset of vapour volume fraction and DNB type CHF. Simulations are further extended to predict CHF in a hexagonal sub-assembly under the influence of blockage. For all the values of blockage, the vapour volume fraction is found to be higher in the corner region, and thus the corner sub-channel experiences CHF. Although DNB type CHF is observed in corner sub-channel, it is noticed that the presence of blockage in the interior sub-channel promotes the coolant mixing and results in higher values of CHF in the corner sub-channel.

Improving the vortex tube parameters using CFD analysis for sustainable manufacturing

Sustainable development will provide innovative methods to lessen manufacturing’s negative environmental effects. Due to the rising desire for a more environmentally conscious populace, sustainability is becoming increasingly crucial in today’s world. Without using power or refrigerant, vortex tubes are a green method of spot cooling. Vortex tubes don’t need to be maintained and are maintenance free. Through this effort, the tube’s parameters will be optimized to raise the cooling temperature. Via CFD study, different vortex tubes with different lengths. Through CFD simulation, the ideal parameters for achieving the lowest cold gas temperature are discovered, including the ideal length of the tube to diameter of the tube ratios, freezing air collection tube diameter (dc), and parameters. By examining the behaviour of vortex tubes with various profiles, length-to-diameter ratios, icy orifice diameters, also a hot end areas using a computerized fluid dynamic tool, it will be possible to demonstrate that they are an alternative and long-lasting instrument for spot cooling in machining operations.

A CFD Study on Intergranular Liquid Feeding and Cracking During Solidification in Welding

A CFD Study on Intergranular Liquid Feeding and Cracking During Solidification in Welding

Drag coefficient on particle agglomerates: a CFD study with experimental validation

Drag coefficient on particle agglomerates: a CFD study with experimental validation

Slug flow in tubular membrane in which air and activated sludge flow: A CFD study

Air bubbles have been widely applied to alleviate membrane fouling of tubular membranes in membrane bioreactors. However, the impact of the air bubbles on the flow at the membrane surface as well as the removal of membrane foulant are not well understood. Therefore, a theoretical computational fluid dynamics model was established to address this. In the model, air and activated sludge flowed at the superficial velocities of 0.7 m/s and 0.3 m/s, respectively. Furthermore, sludge concentrations were 5 g/L and 10 g/L, respectively. The model showed that the activated sludge did not flow downwards in the film zone and eddies were not observed in the zone below the tail of a bubble. The viscosity of sludge varied significantly in the film zone. Mass transfer capacities at membrane surface gradually decreased from the nose to the end of a bubble. Moreover, a lower sludge concentration resulted in a higher mass transfer capacity. The highest shear stress at membrane surface was 14 and 11 Pa, which were significantly higher than the shear stress achieved in submerged membranes being aerated. Microparticles (3–10 µm) at membrane surface could be shifted towards the filtrated bulk solution and sucked at the membrane surface alternatively when a gas slug flowed nearby. Furthermore, the bubbles are not effective in shifting microparticles (<3 µm) toward a bulk solution.

Performance Improvement of Kerosene Fuelled Scramjet Combustor Through Modified Fuel Injection - A Cfd Study

Full scale kerosene fuelled scramjet combustor of a hypersonic air-breathing vehicle is numerically explored for two different fuel injection systems. A commercial software CFXTASCflow has been used for the reacting flow computation within the combustor. Three dimensional Navier-Stokes equations are solved along with k-ε turbulence model to analyse the flow field. Eddy Dissipation Model (EDM) with fast rate chemical kinetics is used for combustion modeling. Lagrangian Particle Tracking Method (LPTM) has been used to simulate the trajectory of the kerosene droplets. Kerosene is injected from the struts. Reacting flow simulations have been carried out for the fuel equivalence ratio of 1.0. The overall flow characteristics in the combustor are presented through the distribution of various thermochemical parameters at different cross sections. Kerosene which is injected in liquid phase completely vaporizes within the combustor. Considerable improvement in the performance in terms of thrust and combustion efficiency is observed with the modified fuel injection system.