Applied Mechanics and Materials Vols. 444-445

Abstract: In this paper, numerical simulation of flow around a cylinder using the feedback force immersed boundary method is carried out. The feasibility of algorithm is verified by the numerical simulation of flow past two cylinders in tandem arrangement. The Cartesian adaptive mesh refinement is used in the whole flow field, and the dynamic distribution characteristics of flow field around a single cylinder and double cylinders are obtained when Re=100. Compared with the results in other literatures, the simulation shows a good agreement.

Abstract: In this study, a Computational Fluid Dynamic (CFD) model is established to obtain the 3-D flow characteristic, temperature distribution of the pressurized water reactor (PWR) upper plenum and hot-legs. In the CFD model, the flow domain includes the upper plenum, the 61 control rod guide tubes, the 40 support columns, the three hot-legs. The inlet boundary located at the exit of the reactor core and the outlet boundary is set at the hot-leg pipes several meters away from upper plenum. The temperature and flow distribution at the inlet boundary are given by sub-channel codes. The computational mesh used in the present work is polyhedron element and a mesh sensitivity study is performed. The RANS equations for incompressible flow is solved with a Realizable k-ε turbulence model using the commercial CFD code STAR-CCM+. The analysis results show that the flow field of the upper plenum is very complex and the temperature distribution at inlet boundary have significant impact to the coolant mixing in the upper plenum as well as the hot-legs. The detailed coolant mixing patterns are important references to design the reactor core fuel management and the internal structure in upper plenum.

Abstract: The extended GAO-YONG turbulence model is used to simulate the flow and heat transfer of flat-plate turbulent boundary layer, and the results indicate that GAO-YONG turbulence model may well describe boundary layer flow and heat transfer from near-wall region to far outer area, without using any empirical coefficients and near-wall treatments, such as wall-function or modified low Reynolds number model, which are used widely in all RANS turbulence models.

Abstract: To research the leakage characteristics and sealing mechanism of the comb labyrinth seals, three-dimensional solutions of NavierStokes governing equations are utilized to investigate the leakage characteristics of the comb Labyrinth for water sealing in leakage flow passage of Francis turbine. The finite volume method is used to discretize the Navier-Stokes equations. The quick scheme and the second central scheme are applied to solve convection and diffusion terms respectively. Distributions of velocity and streamline as well as some flow structure in leakage flow passage are gained at different Reynolds numbers. The results show that vortex generated in the comb consumes kinetic energy and causes the pressure decrease greatly, which play a major role in decreasing the leakage flux.

Abstract: In this paper, Based on the research of CFD basic theory and several key technologies, the numerical model for solving three-dimensional flow field around the open water rudder is proposed. And with the help of computing platform FLUENT, several kinds of numerical simulation of maneuverable movement of NACA0015 rudder have been done. The numerical results are compared with experimental results, showing that the CFD model which is proposed in this paper is suitable for computation of hydrodynamic forces and simulation of the viscous flow around the open water rudder.

Abstract: In order to improve the hydrodynamic performance of the hydrofoil, one new foil is brought forward which has slits near the leading edge and the trailing edge. In this article, the NACA0012 foil whose performance was calculated by CFD method was chose as a study object. And the validity of the CFD method was proved by contrasting the calculation results with the experiments. Through calculating and analyzing the hydrodynamic performance of the new hydrofoil that has suction inlet and jet outlet in the leading edge and the trailing edge respectively, the result shows that such performance of suction-jet hydrofoil has advantages of both suction hydrofoil and water-jet hydrofoil.

Abstract: The upward gas-liquid cross flow around a square cylinder was simulated using two fluid model with the multi-scale turbulent model based on the variable interval time average method. The computational results show that the multi-scale turbulent model can successfully simulate lift coefficient, drag coefficient and vortex shedding characteristics of flow around a body, and can also accurately predict the void fraction distribution and flow structure. Compared with the experimental data, the results of the multi-scale model are better than that of Standard k-ε model and RNG k-ε model. Hence, the study of this paper certificates further that this model can be used in the simulation of the gas-liquid flow around bluff bodies and outher engineering application.

Abstract: The Multi-Stage (MUSTA) scheme was used to construct the numerical fluxes when the hyperbolically degenerate governing equations, in which the independent eigenvectors can not be found, are numerically solved for dilute particle-gas two-phase flows. The abilities of MUSTA scheme used in various problems were analyzed. It was found that the MUSTA scheme is effective even for very complicated problem although appropriate total number of stages should be carefully selected. When the total number of stages equals 3 or 4, the MUSTA scheme is as accurate as Riemann solver in most cases.

Abstract: Based on the unsteady incompressible three-dimensional N-S equations and standard k-ε turbulent model, Sliding Interface Method (SIM) is used to simulate the relative movement between the train and tunnel. The exchange process between the tunnel and the external atmosphere was simulated during the train traveling in subway. Meanwhile, the ventilation capability concerning such factors as train assembly, areas and length of duct were analyzed in detail. Result showed: The schematic of shafts at both end of subway station is more efficiency of ventilation, and improving the train assembly and shortening the length of shaft are helpful to enhance the air exchange of tunnel. In non-air-conditioning, the Open-MTR environmental control system model is feasible. Expanding the area of shaft would not enlarge the air exchange of tunnel efficiently.

Abstract: Using a multiscale model based on the variable interval time average method and a set of averaged equations for incompressible turbulent flows, we simulate the three-dimensional separated and reattaching flow over a swept backward-facing step. The results show that the reattachment length and vortex structure vary with the swept angles from 15° to 60° through a detailed study about velocity profile and pressure distribution. Generally the reattachment length and span wise vorticity decrease dramatically after =30°. The result fully accord with experimental data. Results show that this model is suitable for separated flows, and accurately predict the flow field, so this model should be useful in engineering application.