RANS

—This work presents the numerical simulation and analysis of the turbulent flow over a two-dimensional channel with a backward-facing step. The computational simulation performed in this study is based on the Reynolds equations using a technique denominated Reynolds Average Navier-Stokes (RANS). The main objective of the present work is the comparison of different models of turbulence applied to the turbulent flow over a backward-facing step. The performance of each RANS model used will be discussed and compared with the results obtained through a direct numerical simulation present in the literature. The RANS turbulence models used are k-ω, k-ε, Shear Stress Transport k-ω (SST k-ω) and the second-order closure model called Reynolds Stress Model (RSM). The Reynolds number used in all the numerical simulations constructed in this study is equal to 9000, based on the height of the step h and the inlet velocity U b. The results are the reattachment length, the mean velocity profiles and the turbulence intensities profiles. The k-ε model obtained poor results in most of the analyzed variables in this study. Among the RANS turbulence models, the SST k-ω model presented the best results of reattachment length, mean velocity profile and contour when compared to results obtained in the literature. The RSM model found the best results of turbulence intensity profile, when compared to the models of two partial differential equations that use the Boussines hypothesis.

This paper describes a generalized renormalization group (RNG) turbulence model applied to simulate non-reacting flows in an optical single-cylinder PFI engine. A structured computational mesh of the combustion system with complex geometry was generated by ICEM-CFD in conjunction with KIVA-3V code. Turbulent flow in the 4-valve engine, including the exhaust, intake, compression and expansion strokes, was simulated with the standard k  and a generalized RNG turbulence model using the KIVA-3V code. Crank anglere-solved results from available experimental data were used as the boundary and initial conditions for the calculation setup. Pressure traces of the simulation results were compared to the phase-averaged measured pressure trace. Predicted radial and vertical velocities along a horizontal line at BDC and radial velocities along the cylinder axis at four crank angles were compared with the experimental measurements. In addition, the velocity field calculated by the generalized RNG turbulence model was compared with experimental data from Particle Image Velocimetry (PIV) measurements. Good agreement was found between the experiment results and simulation results with the generalized RNG turbulence model.

Keywords: internal combustion engine, RANS, generalized RNG model, structured grids

The present study tries to analyze the water channel junction, their upstream and
downstream derived hydraulic jump due to an abrupt variation in the liquid flow
phenomenon from the Supercritical to Subcritical stage, and that transforms the water
into a gaseous form without any indication or visible phase changeover. A hydraulic
jump condition explained as a significant loss of head, manifesting the available
energy to act, scour and generate turbulence. The Triple Point phase position
coexisting in equilibrium is created at the three diverse phases interaction point,
where liquid, solid, and gaseous states of water coexist in a stable equilibrium. The
water depth measurements for the simulation of the CFD was developed and further
equated with experimental
averaged Navier-Stoke called RANS, derives the turbulence model, and various
hydraulic jumps applied to the turbulent flow explained. The numerical simulation
results concluding design provide very support
type of model, definitely showing the CFD ability to simulate the complicated
condition of fluid phenomenon. In the methodology, highly common modelling and
application is shown in the water flow equations in the ope
Hydraulic Jump Process.

This paper presents numerical results of the DU-91-W2-250 airfoil. Reynolds-averaged Navier–Stokes (RANS) simulations of the 2D profile are performed employing the Transient SST turbulence model. The airfoil was investigated for the Reynolds number of 6·10 6. Lift and drag coefficients are compared with the experimental data from LM Low Speed Wind Tunnel (LSWT). The results of lift and drag coefficients obtained using the SST Transient model are in a good agreement in comparison with the experiment in the angle of attack range from-10° to 10°. The static pressure distributions calculated by the SST Transition model are also in good agreement with the experiment.

A computational investigation of thermal plume is important because such flows are encountered in various industrial applications. The investigation is also important because thermal plume can be considered as a test case for modeling of fire which can help designers and safety engineers to develop preventive measures and fire safety systems. The present study primarily focuses on the investigation of thermal buoyant plume in the self-similar region. In the present study, an assessment of three buoyancy-corrected turbulence models, namely k-ω, the standard k-ε model and the RNG k-ε model, has been conducted for a thermal buoyant plume. Modifications to the turbulence models have been made to account for the effect of buoyancy on the production and dissipation of turbulent kinetic energy and these modifications are based on the simple gradient-diffusion hypothesis and generalized gradient-diffusion hypothesis. The model based on the simple gradient diffusion hypothesis is shown to under-predict contribution to the generation of turbulence kinetic energy due to buoyancy. A comparison with the experimental measurements reported in the literature shows that the generalized gradient-diffusion hypothesis along with both turbulence models correctly predicts the mean flow field, temperature field and spread rates. The results of the present simulations using the RNG k-ε model with the generalized gradient-diffusion hypothesis are shown to be in good agreement with the corresponding experimental results reported in the literature for thermal plumes.

Keywords: plume, buoyancy, RANS, turbulence modelling, natural convection

Fluid flow around a NACA 4412 airfoil in a wind tunnel test section at Reynolds number of 3 x 106, based on the chord of the airfoil (150 mm) and free stream velocity (30 m/s), is considered. The study covers the boundary layers around the airfoil and the wake region at different angles of attack. Different turbulence models are used to predict separated flows over the airfoil. Two-equation turbulence models, k-ω and k-ε, and Reynolds Stress Model are tested for the ability to predict boundary layer separation on the airfoil. Reynolds Stress model captured the physics of separated flow favourably, and gave a very realistic evolution of the vortex formed due to separation. Statistics of the flow which is generated by RSM are in good agreement with an existing wind tunnel experimental data. The flow field which is generated by the two-equation turbulence models poorly predicted flow separation and vortex dynamics and consequently overestimated the lift coefficient for angles of attack larger than the critical angle of attack.

This paper presents a feasibility study of a hybrid RANS-LES approach to numerical simulation of aircraft wing-tip vortices. A NACA 0012 wing is considered for which earlier published experimental and numerical data are available. Mesh sensitivity tests of our RANS solver and comparisons between two different turbulence models indicate that the RANS approach adequately describes the flow upstream from the trailing edge, but overestimates the rate of decay of the wing-tip vortex. A hybrid RANS-LES method is presented that results in a better agreement with the wind tunnel experiment, hence this approach is suggested for numerical simulation of the wake of an airliner.

A numerical investigation was carried out to determine the impact of structural morphology on the power generation capacity of building-integrated wind turbines. The performance of the turbines was analysed using the specifications of the Bahrain Trade Centre which was taken as the benchmark model, the results of which were compared against triangular, square and circular cross-sections of the same building. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations along with the momentum and continuity equations were solved for obtaining the velocity and pressure field. Simulating a reference wind speed of 6 m/s, the findings from the study quantified an estimate power generation of 6.4 kW indicating a capacity factor of 2.9 % for the benchmark model. The square and circular configurations however determined greater capacity factors of 12.2 % and 19.9 %, recording an estimated power production capability of 26.9 kW and 35.1 kW and confirming the largest extraction of the incoming wind stream. The optimum cross-sectional configuration for installing wind turbines in high-rise buildings was the circular orientation as the average wind speed at the wind turbines was accelerated by 0.3 m/s resulting in an overall augmentation of 5 %. The results from this study therefore highlighted that circular building morphology is the most viable building orientation, particularly suited to regions with a dominant prevailing wind direction.