离散统一气体动理学算法(Discrete Unified Gas Kinetic Scheme,DUGKS)是一种多尺度计算流体力学方法,该方法适用于所有流域的流体力学模拟。在三维不可压缩热流体的仿真中,原始双分布DUGKS的算法结构较为复杂,且时间步长受限于较小的CF...离散统一气体动理学算法(Discrete Unified Gas Kinetic Scheme,DUGKS)是一种多尺度计算流体力学方法,该方法适用于所有流域的流体力学模拟。在三维不可压缩热流体的仿真中,原始双分布DUGKS的算法结构较为复杂,且时间步长受限于较小的CFL数(CFL<1),其计算效率亟待提升。在对原始DUGKS的研究中发现,可以通过改变原始算法中对微通量的求解方式来优化算法结构,发展一种三维热流体简化DUGKS。理论上,简化DUGKS可以使计算量节约50%左右。三维自然对流的数值模拟结果则进一步表明:在相同的计算网格和时间步长下,简化DUGKS的数值精度与原始DUGKS相当,其计算速度接近原始DUGKS的2倍;简化DUGKS在CFL数为1.7时仍能获得精确的预测结果,采用较大的时间步长可以使计算成本进一步节约70%。算法结构的简化和数值稳定性的提高使DUGKS的计算效率大幅提升。展开更多
This paper focuses on the impacts of convective momentum transport(CMT) on simulations of the tropical intraseasonal oscillation(TIO) in SAMIL. Two sets of experiments are performed, which give different reality of th...This paper focuses on the impacts of convective momentum transport(CMT) on simulations of the tropical intraseasonal oscillation(TIO) in SAMIL. Two sets of experiments are performed, which give different reality of the Madden-Julian Oscillation(MJO). The Tiedtke cumulus parameterization scheme is used for all experiments. It is found that simulations of the TIO can be influenced by CMT, and the impacts on the simulated TIO depend on the model capability in simulating the MJO. CMT tends to have large influences to the model that can simulate the eastward propagation of the MJO. CMT can further influence the long-term mean of zonal wind and its vertical shear. Zonal wind suffers from easterlies biases at low level and westerlies biases at upper level when CMT is introduced. Such easterlies biases at low level reduce the reality of the simulated tropical intraseasonal oscillation. When CMT is introduced in the model, MJO signals disappear but the model's mean state improves. Therefore, a more appropriate way is needed to introduce CMT to the model to balance the simulated mean state and TIO signals.展开更多
A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried...A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried out in order to model and simulate the combination of a two-phase flow with evaporation in a vertical tube. The VOF （volume-of-fluid） multiphase flow method and a phase-change model for the mass transfer have been used. For an accurate modeling, the effect of axial conduction has been also taken into account using a conjugate heat transfer model. Since thermal oscillations are undesirable as they can lead to the failure of the tube, flow instabilities have also been analyzed, using FFT （fast Fourier transforms）, in order to comprehend their behavior and influence. A control study of the flow instabilities in the tube is also presented. For that purpose tube inlet temperature has been varied using a gain control parameter.展开更多
文摘离散统一气体动理学算法(Discrete Unified Gas Kinetic Scheme,DUGKS)是一种多尺度计算流体力学方法,该方法适用于所有流域的流体力学模拟。在三维不可压缩热流体的仿真中,原始双分布DUGKS的算法结构较为复杂,且时间步长受限于较小的CFL数(CFL<1),其计算效率亟待提升。在对原始DUGKS的研究中发现,可以通过改变原始算法中对微通量的求解方式来优化算法结构,发展一种三维热流体简化DUGKS。理论上,简化DUGKS可以使计算量节约50%左右。三维自然对流的数值模拟结果则进一步表明:在相同的计算网格和时间步长下,简化DUGKS的数值精度与原始DUGKS相当,其计算速度接近原始DUGKS的2倍;简化DUGKS在CFL数为1.7时仍能获得精确的预测结果,采用较大的时间步长可以使计算成本进一步节约70%。算法结构的简化和数值稳定性的提高使DUGKS的计算效率大幅提升。
基金sponsored by the Joint Project of Natural Science Foundation of China and Yunnan Province (U0833602)
文摘This paper focuses on the impacts of convective momentum transport(CMT) on simulations of the tropical intraseasonal oscillation(TIO) in SAMIL. Two sets of experiments are performed, which give different reality of the Madden-Julian Oscillation(MJO). The Tiedtke cumulus parameterization scheme is used for all experiments. It is found that simulations of the TIO can be influenced by CMT, and the impacts on the simulated TIO depend on the model capability in simulating the MJO. CMT tends to have large influences to the model that can simulate the eastward propagation of the MJO. CMT can further influence the long-term mean of zonal wind and its vertical shear. Zonal wind suffers from easterlies biases at low level and westerlies biases at upper level when CMT is introduced. Such easterlies biases at low level reduce the reality of the simulated tropical intraseasonal oscillation. When CMT is introduced in the model, MJO signals disappear but the model's mean state improves. Therefore, a more appropriate way is needed to introduce CMT to the model to balance the simulated mean state and TIO signals.
文摘A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried out in order to model and simulate the combination of a two-phase flow with evaporation in a vertical tube. The VOF （volume-of-fluid） multiphase flow method and a phase-change model for the mass transfer have been used. For an accurate modeling, the effect of axial conduction has been also taken into account using a conjugate heat transfer model. Since thermal oscillations are undesirable as they can lead to the failure of the tube, flow instabilities have also been analyzed, using FFT （fast Fourier transforms）, in order to comprehend their behavior and influence. A control study of the flow instabilities in the tube is also presented. For that purpose tube inlet temperature has been varied using a gain control parameter.
