Papers by Keyword: Turbulence Model

Abstract: Flow past a two-dimensional D-shaped bluff body is numerically studied. This study uses two turbulence models, the standard k-ε turbulence model and the Shear Stress Transport (SST) turbulence model to simulate the fluid flow inside the computational domain. This study focuses on the pressure distribution on the D-shaped body and the wake region behind the bluff body. Variation of centreline mean velocity, variation of mean velocity profile and the wake half-width in the wake region are also investigated and the results are compared with experimental results available in the literature. The computational fluid dynamics software EASYCFD, which uses a finite-volume based discretization method is chosen to solve the governing equations. The first order upwind method is used to discretize the momentum equations, turbulent kinetic energy and turbulence dissipation rate equations. The Semi-Implicit Method for Pressure-Linked Equations-Consistent (SIMPLEC) method is implemented for the pressure velocity interactions. Numerical results show that the two turbulence models perform reasonably well in predicting this complex fluid flow. The drag coefficient of the bluff body has been calculated to be 0.758 and 0.679 using the standard k-ε and the Shear Stress Transport (SST) turbulence models respectively.

Abstract: An idea of introducing an underground floodway inspired by Storm-water Management and Road Tunnel (SMART) in Malaysia is considered attractive to minimize land utilization regarding to the flood problem in Jakarta. This research was aimed to know the flow behavior of this modified tunnel due to sudden transitions, pressure losses and loss coefficients using numerical modeling. The simulation was conducted in the three-dimensional model using FLUENT Software which was divided into three models, i.e., contraction, enlargement, and straight pipe model. The simulation model was followed the geometrical design of SMART which the area ratio between smaller and larger pipe, A₁/A₂ varied, namely 0.20, 0.50, and 0.80. Standard k-ε and equilibrium wall function were used in straight pipe model, while contraction and enlargement model used k-ε modified and non-equilibrium wall function. The effect of different Reynolds number was also studied in this research. The result of the simulation showed that hydraulic parameters and area ratio of sudden transitions pipe give significant effect towards losses along the pipe. FLUENT simulation result gave good agreement with Darcy-Weisbach formula. The results indicate that loss coefficient decreases with the increase in pipe area ratio. The increase in pressure head loss was incurred by severe separated regions in the vicinity of pipe transition which was proved by typical flow pattern. Variation of Reynolds number also showed a different area of separation flow, yet the flow pattern was somewhat similar.

Abstract: In order to evaluate the performance of airfoils with computational fluid dynamics (CFD) tools, modelling of transitional region in the boundary layer is very critical. Currently, there are several classes of transition-based turbulence model which are based on different methods. Among these, the k-k_L- ω, which is a three equation turbulence model, is one of the prominent ones which is based on the concept of laminar kinetic energy. This model is phenomenological and has several advantageous features. Over the years, different researchers have attempted to modify the original version which was proposed by Walter and Cokljat in 2008 to enrich the modelling capability. In this article, a modified form of k-k_L-ω transitional turbulence model has been used with the help of OpenFOAM for an investigative CFD analysis of a NACA 4-digit airfoil at range of angles of attack.

Abstract: A gas-solid multiphase flow is simulated using CFD to investigate the fluid dynamics of a fluidized bed reactor. The simulation is based on Euler-Euler two fluid model where Kinetic Theory of Granular Flow is used for predicting the solid phase transport properties. The simulation procedure is validated by reproducing and comparing hydrodynamic parameters with those available in the literature. The effect of different turbulence models on bed fluid dynamics is analyzed and k-ε RNG per-phase model is found to have better prediction accuracy compared to other models. The minimum fluidization velocity, granular temperature, bed expansion, particle velocity and volume fraction are determined by the model.

Abstract: The numerical study of the two-dimensional supersonic hydrogen-air mixing in the free shear layer is performed. The system of the Favre-Averaged Navier-Stokes equations for multispecies flow is solved using the ENO scheme of the third order accuracy. The k-ε two-equation turbulence models with compressibility correction are applied to calculate the eddy viscosity coefficient. The dispersion of the particles is studied by following their trajectories in the shear layer by Euler method. In order to produce the roll-up and pairing vortex rings, an unsteady boundary condition is applied at the inlet plane. At the outflow, the non-reflecting boundary condition is taken. The influence of different Mach numbers on the formation of vorticity structures and shear layer growth rate are studied. The obtained results are compared with the available experimental data and the numerical results of other authors. The numerical simulation of the particle dispersion in the shear layer with large scale vortical structure is conducted.

Abstract: In general, the turbulent flow inside PWR (Pressurized Water Reactor) fuel assembly depends on the mixing vane configuration and the pattern of the mixing vane arrangement on the strap of the spacer grid. In this study, in order to examine the turbulent flow structure inside fuel assembly with the split-type mixing vanes, simulations were conducted with the commercial CFD (Computational Fluid Dynamics) software, ANSYS CFX R.14. Two different types of turbulence models, i.e. SAS (Scale-Adaptive Simulation)-SST (Shear Stress Transport) and DES (Detached Eddy Simulation), were used. The predicted results were compared with the measured data from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. Although there were locally differences between the prediction and the measurement, ANSYS CFX R.14 predicted the time averaged velocity field in the reliable level. The predicted horizontal and vertical velocity components were more in agreement with the measured data than the axial velocity component. There was no significant difference in the prediction accuracy of both turbulence models.

Abstract: In recent years, people pay increasing attention to the issue whether indoor air conditioning system can meet the requirements of thermal comfort under the circumstance of good air quality and reduce energy consumption. FLUENT, commercial computational fluid dynamics software is used to simulate the three-dimensional distribution of temperature and velocity in the subject hotel atrium. The turbulence model modified by buoyancy was used to solve equations. The SIMPLE scheme was used for numerical discrimination. Distribution of temperature, velocity on some typical section and the atrium space can be obtained; the result of numerical simulation can be visualized by post-processing module of FLUENT and TECPLOT software. The influence to the air flow distribution is simulated and calculated by the elements of different rates, angle, and height of the air supply flow. As for the specified case of the project, an optimized solution is obtained, that is supply air speed 6 m/s, angle 15°, air inlet height 7.5m, air temperature 291K.

Abstract: The codes for ejector nozzle with floating external adjustment sheet were specially developed, the flow field was numerically simulated by using parametric modeling method and grid partitioning technique. Turbulence model was selected according to predictions of explicit algebraic Reynolds stress, specific heat ratio (γ) was based on local temperature and gas compositions. The formulas of ideal nozzle parameters were derived using varied γ, which were used to analyze nozzle aerodynamic performance. The results obtained from constant and variable γ were compared. The results show that: nozzle mass flow rate is reduced because of more difficulty in airflow expansion, while nozzle thrust has a tiny change in variable γ cases. Moreover, the high temperature region of inner nozzle is larger and injected cold air is less despite of a smaller balanced floating sheet angle, which are detrimental to thermal protection.

Abstract: Dense flow absorber of desulfurization is a new type of semi dry flue gas desulfurization technology, desulfurization of flue gas is mainly in the dense phase absorption tower. By using the turbulence model in Fluent.14 software, three-dimensional numerical simulation of dense phase in different flue gas entrance tower height of internal flow field. Selection of k- ε model as the calculation model, using Simple algorithm. Selected from the flue gas 1m, 2mand 3m, simulation the flow field distribution, combined with the experimental analysis.The results show that the flue gas entrance height from the top of the 1m, the flow field distribution is uniform, the minimum pressure drop.

Abstract: The Steady flow simulation to selected the delta wing model for different angles of attack in the Maher number.The law of flow field changes with the angle of attack is gotten.Through the FLUENT simulation,The variation tendency of coefficient of lift and drag in the different angle of attack is gotten.Further reveals the change rule of Maher number, pressure, velocity and other parameters in the different angle of attack.With increasing angle of attack, Maher number distribution is sparse of the same position increases and the greater numerical.the distribution of velocity vector is sparse of the same position increases and the greater numerical.the pressure distribution is sparse of the same position increases and the greater numerical.