Numerical simulation of shock wave propagation using the finite difference lattice Boltzmann method

The shock wave process represents an abrupt change in fluid properties, in which finite variations in pressure, temperature, and density occur over the shock thickness which is comparable to the mean free path of the gas molecules involved. This shock wave fluid phenomenon is simulated by using the finite difference lattice Boltzmann method (FDLBM). In this paper, a new model is proposed using the lattice BGK compressible fluid model in FDLBM for the purpose of speeding up the calculation as well as stabilizing the numerical scheme. The numerical results of the proposed model show good agreement with the theoretical predictions.     

Numerical Prediction of Acoustic Sounds Occurring by the Flow Around a Circular Cylinder

Acoustic sounds generated by uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. A third-order-accurate up-wind scheme is used for the spartial derivatives. A second-order-accurate RungeKutta scheme is also used for time marching. Very small acoustic pressure fluctuation, with same frequency as that of Karman vortex street, is compared with pressure fluctuation around a circular cylinder. The propagation velocity of acoustic sound shows that acoustic approaching the upstream, due to the Doppler effect in uniform flow, slowly propagates. For the downstream, on the other hand, it quickly propagates. It is also apparent that the size of sound pressure is proportional to the central distance τ^-1/2 of the circular cylinder.     

Investigation of the flow field developed behind a planar shock wave propagating into a reactive gas solid suspension

The equations governing the flow-field which is developed when a moderately strong shock wave propagates in an oxygencarbon suspens on were developed and solved numerically. The energy transfer which takes place between the shocked gas and the solid carbon particles causes ignition of the particls. The resulting flow-field properties are shown at different times.     

CFD软件在对旋式轴流风机数值模拟中的应用

综合分析介绍了CFD软件在叶轮机械数值模拟中的两个关键问题,即数值算法和湍流模型及其最近的一些研究进展,并以对旋式轴流风机的数值模拟为例对其应用进行了举例说明,最后对CFD在叶轮机械数值模拟中的应用及发展趋势进行了展望.     

Numerical simulation of droplet formation in a micro-channel using the lattice Boltzmann method

This study investigates droplet formation in a micro-channel using the lattice Boltzmann (LB) method. A cross-junction micro-channel and two immiscible, water and oil phase fluids, were used to form the micro-droplets. Droplets are formed by the hydrodynamic instability on the interface between two immiscible fluids when two immiscible fluids are imported simultaneously in a cross-junction micro-channel. The Shan & Chen model, which is a lattice Boltzmann model of two-phase flows, is used to treat the interaction between immiscible fluids. The detailed process of the droplet formation in the cross-junction micro-channel was illustrated. The results of the droplet formation by the LBM predicted well the experimental data by PIV (particle image velocimetry). The effect of the surface tension and the flow rate of water phase fluid on the droplet length and the interval between droplets was also investigated. As the surface tension increased, the droplet length and the interval between droplets were increased. On the other hand, when we increased the flow rate of the water phase fluid under the condition of the fixed oil-phase fluid flow rate, the droplet size was increased while the interval between droplets was decreased.     

The effect of blade angle on the flow and pressure distributions in the vicinity of the diffuser blades of a room air conditioner

Many studies on air-conditioning systems are more focused on the individual thermal comfort rather than the thermal efficiency, due to an increase in health concerns. There are several factors influencing the thermal comfort, such as temperature, humidity, convection and air movement, etc. Numerical analyses were performed to investigate the effect of blade angle on the flow characteristics in the vicinity of diffuser blades of a room air conditioner (RAC), with three different blade discharge angles of 45.1°, 58.6° and 116°. We used the commercial code FLUENT to calculate the two-dimensional steady thermal flow fields with different impeller rotational velocities. The angular velocities were located within the range from 900 rpm to 1200 rpm. Turbulence closure was achieved using a standard k-ɛ model. A moving reference frame (MRF) approach was adopted to simulate the flow field generated by the impeller in an RAC. The results were graphically depicted with various geometrical configurations and operating conditions. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Youn-Jea Kim received his B.S. degree in Mechanical Engineering from Sungkyunkwan University, Korea, in 1982. He then received his M.S. and Ph.D. degrees from the State University of New York at Buffalo in 1987 and 1990, respectively. Dr. Kim is currently a Professor at the School of Mechanical Engineering at Sungkyunkwan University in Korea. Dr. Kim’s research interests include gas dynamics, MEMS, and fluid-machineries, etc.     

正弦波纹流道中流体流动和传热特性研究

采用计算流体力学(CFD)方法,研究了一定雷诺数范围内(50≤Re≤200),正弦波纹流道内的流体充分发展的层流流动和传热性能。比较了不同结构的正弦波纹流道的阻力因子ef、传热因子eNu和能效因子e的值,研究结果表明,正弦波纹流道的波纹波幅对于流体流动和传热性能的影响较大。分析了波纹流道中垂直于主流方向特殊横截面上的流体速度矢量图和温度等值线图,研究结果表明,波纹流道的弯曲壁面使得流体在流道中垂直于主流方向的截面上产生二次流,二次流的出现增强了流道中心流体和近壁处流体的混合和传热,传热性能提高的同时阻力增加。     

Computational study of the mixed cooling effects on the in-vessel retention of a molten pool in a nuclear reactor

The retention of a molten pool vessel cooled by internal vessel reflooding and/or external vessel reactor cavity flooding has been considered as one of severe accident management strategies. The present numerical study investigates the effect of both internal and external vessel mixed cooling on an internally heated molten pool. The molten pool is confined in a hemispherical vessel with reference to the thermal behavior of the vessel wall. In this study, our numerical model used a scaled-down reactor vessel of a KSNP (Korea Standard Nuclear Power) reactor design of 1000 MWe (a Pressurized Water Reactor with a large and dry containment). Well-known temperature-dependent boiling heat transfer curves are applied to the internal and external vessel cooling boundaries. Radiative heat transfer has been considered in the case of dry internal vessel boundary condition. Computational results show that the external cooling vessel boundary conditions have better effectiveness than internal vessel cooling in the retention of the melt pool vessel failure.