Papers by Keyword: Turbulent Model

Abstract: A solver for MHD turbulent flow and a new RANS model based on k-ω model in the open source toolbox OpenFOAM are developed to investigate magnetohydrodynamic (MHD) turbulent flow. Two electro-magnetic terms in the k and ω transport equations are added to include magnetohydrodynamic (MHD) effects. The modified k-ω is validated by simulating MHD turbulent duct flow. Time-averaged velocity and turbulent kinetic energy profiles simulated by standard k-ω and the modified k-ω in the fully developed section are both reported. The results compare fairly with those obtained from DNS data. A difference of 8.4% in is found between the modified k-ω and DNS, but the RANS model only uses 0.4% of the DNS computation time.

Abstract: VOF model and turbulent model were used in this paper to study on flow characteristic inside a certain spillway tunnel of hydropower station, which includes cross sectional distributions of flow velocity in pressure section and non-pressure section. The results show that flow velocity distribution in the pressure section of the spillway tunnel is basically symmetrical. After turning, flow velocity is well-distributed and move ahead; flow velocity in the right side of non-pressure section in the spillway tunnel is 1m/s faster than that in the left side. When two high-speed water flow come together after passing through the central division pier, flow velocity distributions in the both sides of the spillway tunnel are all uniform. The conclusions obtained can improve the design of the spillway tunnel.

Abstract: Flow structure over bluff bodies is more complex in wake. The wake is characterized by the unsteady behavior of the flow, large scale turbulent structure and strong recirculation region. For the case of high speed train, wake can be observed at the gap between the coaches and also on the rear coach. Wakes formation of high speed train are generated by free shear layer that is originated from the flow separation due to the sudden change in geometry. RANS and LES turbulent models are used in this paper to stimulate the formation of wakes and behavior of the flow over a simplified high speed train model. This model consists of two coaches with the gap between them is 0.5D. A total of four simulations have been made to study the effect of computational domain size and grid resolution on wake profiles of a simplified high speed train. The result shows that the computational domain can be reduced by decreasing the ground distance to 1.5D without affecting the magnitude of the wake profile. Both RANS and LES can capture the formation of the wake, but LES requires further grid refinement as the results between the two grid resolutions are grid dependent.

Abstract: The last years have proved that Vertical Axis Wind Turbines (VAWTs) are more suitable for urban areas than Horizontal Axis Wind Turbines (HAWTs). To date, very little has been published in this area to assess good performance and lifetime of VAWTs either in open or urban areas. The main goal of this current research is to investigate numerically the aerodynamic performance of a newly designed cavity type vertical axis wind turbine having four blades. In the current new design the power generated depends on the drag force generated by the individual blades and interactions between them in a rotating configuration. For numerical investigation, commercially available computational fluid dynamic CFD software GAMBIT and FLUENT were used. In this numerical analysis the Shear Stress Transport (SST) k-ω turbulence model is used which is better than the other turbulence models available as suggested by some researchers. The computed results show good agreement with published experimental results.

Abstract: Natural convective heat transfer is the most important means to supply heat load for resident building to keep necessary indoor air temperature in winter. To determine the surface convective heat transfer coefficient (CHTC) of a radiator is of primary importance to evaluate the heat flow within building interiors, and thereby to affect the thermal comfort and the overall energy consumption of a building. In this paper, a turbulent k-ε model is used to numerically analyze the heat transfer characteristics of a radiator used in a heating room in Lanzhou region of China. The results indicate that the averaged Nu number of radiator surface increases with increasing outer wall thermal conductivity, decreasing outdoor temperature and decreasing radiator surface area, respectively. And the outer wall thermal conductivity has weak influence on the local Nu number of radiator surface.

Abstract: This paper mainly studies at the different way of ventilation to the influence of air distribution in the large size plenum. The model is a grand theatre stalls. To model the plenum which under the grand theatre stalls,and took out the size of large mutations alone modeling and studying it. the six different way of ventilation: small plenum with four directions supply air; Take a duct with four tuyere on supply air; Single tuyere withside air supply; Tuyere parallel supply air; Single tuyere with air supply under; Take a duct with four draught under supply air have influence of air distribution.And combined with the well of heat insulation in the large size plenum.It can use the standard RNG turbulence model, and the pressure interpolation adopt standard discrete format, the convection item of the momentum equations, k equation, ε equation adopt with second order the format. the pressure speed coupling adopt Simple algorithm. Finally through the FLUENT software were used. It can use the air balance coefficient wich is one evaluation index to analyz Simulation results of the Six air distribution mode . Through the analysis and comparison with a wind that four tuyere air supply under Static pressure boxair supply the best effect, the static pressure air distribution most evenly

Abstract: In HDD air flow simulation, the well known LES turbulent model requires large computing times and resources, including CPU, RAM and storage intensive which is not appropriate when using various variables. The effect of an air damper is studied by the k-e model with a reduced boundary due to the lower number of equations, computing time and computer resources. Firstly the RMS velocities of a partial model are compared between LES and k-e and then the reduced boundary models are compared with the partial model. The RMS velocity errors of the partial model compared with LES and k-e are less than 6 %. The mean RMS velocity errors compared with the reduced boundary model and the partial model are 3.93% at ID and 2.12% at MD position while the OD position increased to 26.5% because there is no effect from a return flow from the flex bracket and voice coil zone. Computing time of the reduced boundary and k-e model is reduced by 68.4%. In primary HDD air flow analysis, the k-e method together with a reduced model can be used to predict the effect of an air damper.

Abstract: Four turbulent models are introduced. The hypersonic aerodynamic heating calculation results by Shear Stress Transport (SST) turbulent model of different grid scale shows that near wall y+ spacing approximate to one third of the upper limit prescribed by turbulent model. Then, the comparison of the hypersonic aerodynamic heating calculation results by different turbulent model and the test data shows that SST turbulent model can give an enough accurate result.

Abstract: Averaging pitot tube has been applied in practice more often in these years. This paper set up the two-dimensional model of the bullet-shaped averaging pitot tube, numerical simulation based on CFD was used to investigate the changes of flow coefficient along with the Reynolds number. The geometric size of the section was changed to investigate how it influences the flow coefficient and differential pressure. To guarantee the accuracy of the simulation, the grid and the simulation model were investigated too.

Abstract: In order to complete the numerical simulation on internal flow and operating characteristics of down hole multiphase pump compress unit, establishing perfect finite element model, the three-dimensional turbulent current fields inside the impellers of compression unit for down hole multiphase pumps were simulated by using ANSYS. The calculation of multiphase flow is based on the standard k-ε turbulent current model. Reference information for the improvement of the pump can be obtained by the analysis of the flow of gas-oil in the channel of pump. Based on the finite method, we analyzed several situations in a pumping period. The velocity and liquid pressure distributing of sucker rod pump is studied in this paper, which may offer some evidences for the engineering design of sucker rod pump.