We present a highly efficient lattice Boltzmann model for simulating compressible Hows.This model isbased on the combination of an appropriate finite difference scheme,a 16-discrete-velocity model[Kataoka and Tsutahar...We present a highly efficient lattice Boltzmann model for simulating compressible Hows.This model isbased on the combination of an appropriate finite difference scheme,a 16-discrete-velocity model[Kataoka and Tsutahara,Phys.Rev.E 69(2004)035701(R)]and reasonable dispersion and dissipation terms.The dispersion term effectivelyreduces the oscillation at the discontinuity and enhances numerical precision.The dissipation term makes the new modelmore easily meet with the von Neumann stability condition.This model works for both high-speed and low-speed flowswith arbitrary specific-heat-ratio.With the new model simulation results for the well-known benchmark problems geta high accuracy compared with the analytic or experimental ones.The used benchmark tests include(i)Shock tubessuch as the Sod,Lax,Sjogreen,Colella explosion wave,and collision of two strong shocks,(ii)Regular and Mach shockreflections,and(iii)Shock wave reaction on cylindrical bubble problems.With a more realistic equation of state orfree-energy functional,the new model has the potential tostudy the complex procedure of shock wave reaction on porousmaterials.展开更多
In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow stru...In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow structures, and a particle image velocimetry (PIV) technique is applied to the measurement of the time-averaged and instantaneous velocity and vorticity fields. The results show that the unsteadiness of mass transfer process between the vapor and the two-phase regions is substantial, a self-oscillatory behavior of the whole sheet cavitation is obtained, with large length fluctuations and vapor cloud shedding, and also the cavitation structure depends on the interaction of the water-vapor mixture and the periodic vortex shedding. The main purpose of this experimental study is to offer information for validating computational models, and shed light on the unsteady multiphase transport process of cavitating flows. Furthermore, with an emphasis on the dynamics of the attached turbulent cavitating flows, a filter-based model (FBM) is derived from the ktwo-equation model, a conditional averaging method aimed at improving unsteady simulation is applied to computation. In comparison to the standard kmodel, overall, the filter-based model is shown to improve the predictive capability considerably.展开更多
To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RAN...To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction.展开更多
基金Supported by the Science Foundations of LCP and CAEP under Grant Nos.2009A0102005 and 2009B0101012the National Basic Research Program (973 Program) under Grant No.2007CB815105the National Natural Science Foundation under Grant Nos.10775018,10702010,and 10775088
文摘We present a highly efficient lattice Boltzmann model for simulating compressible Hows.This model isbased on the combination of an appropriate finite difference scheme,a 16-discrete-velocity model[Kataoka and Tsutahara,Phys.Rev.E 69(2004)035701(R)]and reasonable dispersion and dissipation terms.The dispersion term effectivelyreduces the oscillation at the discontinuity and enhances numerical precision.The dissipation term makes the new modelmore easily meet with the von Neumann stability condition.This model works for both high-speed and low-speed flowswith arbitrary specific-heat-ratio.With the new model simulation results for the well-known benchmark problems geta high accuracy compared with the analytic or experimental ones.The used benchmark tests include(i)Shock tubessuch as the Sod,Lax,Sjogreen,Colella explosion wave,and collision of two strong shocks,(ii)Regular and Mach shockreflections,and(iii)Shock wave reaction on cylindrical bubble problems.With a more realistic equation of state orfree-energy functional,the new model has the potential tostudy the complex procedure of shock wave reaction on porousmaterials.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50679001 and 50979004)
文摘In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow structures, and a particle image velocimetry (PIV) technique is applied to the measurement of the time-averaged and instantaneous velocity and vorticity fields. The results show that the unsteadiness of mass transfer process between the vapor and the two-phase regions is substantial, a self-oscillatory behavior of the whole sheet cavitation is obtained, with large length fluctuations and vapor cloud shedding, and also the cavitation structure depends on the interaction of the water-vapor mixture and the periodic vortex shedding. The main purpose of this experimental study is to offer information for validating computational models, and shed light on the unsteady multiphase transport process of cavitating flows. Furthermore, with an emphasis on the dynamics of the attached turbulent cavitating flows, a filter-based model (FBM) is derived from the ktwo-equation model, a conditional averaging method aimed at improving unsteady simulation is applied to computation. In comparison to the standard kmodel, overall, the filter-based model is shown to improve the predictive capability considerably.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51236006, 51576153)
文摘To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction.
