高雷诺数湍流风场大涡模拟的并行直接求解方法
PARALLEL DIRECT METHOD OF LES FOR TURBULENT WIND FIELD WITH HIGH REYNOLDS NUMBER
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摘要: 在环境流体力学中,风场是风沙流、风雪流等自然环境特性问题研究的动力源和基础. 通常采用壁湍流模型进行风场大涡模拟(large eddy simulation, LES)计算,但受到计算规模的限制使得 高雷诺数风场的模拟计算难以实现. 并行计算技术是解决大规模高雷诺数风场大涡模拟的关键技术之一. 在不可压湍流风场的LES模拟中,压力泊松方程的并行计算技术是进行规模并行计算的困难点. 根据风场流动模拟计算的特点,采用水平网格等距而垂直于地面网格非等距,在解决规模并行计算中求解压力泊松方程的难点问题时,利用FFT解耦三维泊松方程使其变为垂向的一维三对角方程, 并利用可并行的三对角方程PDD求解技术,可建立三维泊松方程的直接并行求解技术. 结合其它容易并行的动量方程计算,本文建立风场LES模拟的并行直接求解方法(parallel direct method-LES, PDM-LES). 在超级计算机上对新方法进行并行效率测试,并行计算效率达到90\%. 新的方法可用于进行湍流风场大涡模拟的大规模并行计算. 计算结果表明,湍流风场瞬时速度分布近壁面存在条带状的拟序结构,平均场的速度分布符合速度对数律特性,风场湍流特性基本合理.Abstract: In the environmental fluid mechanics, the turbulent wind field in the atmospheric layer is the driving force and the foundation for the study of the natural environment characteristics such as the wind and sand flow and the wind and snow flow. The calculation simulation of the turbulent wind field is usually used the turbulent boundary layer model, where the large eddy simulation (LES) is an effective computational tool. The parallel computing technology is one of the key technologies for the LES simulation to solve the large-scale turbulent wind field with the high Reynolds number. In the LES simulation of the turbulent wind field, the parallel computing technique of the pressure Poisson equation is the difficult point for the scale parallel calculation. Based on the characteristics of the turbulent wind field flow simulation, the horizontal grids are equidistant spacing and the grids perpendicular to the ground are non-equidistant. Using the FFT decoupling three-dimensional Poisson equation to make it a one-dimensional three-dimensional diagonal equation, and the parallel-able PDD technology is used to solve the three-diagonal equation for solving the difficult problem of the pressure Poisson equation in the scale parallel calculation, and the three-dimensional pressure Poisson equation can be solved directly in parallel. Combined with the other parallel momentum equation calculations, the parallel direct method of LES (PDM-LES) for the turbulent wind field simulation is established. The new method is tested in parallel on the supercomputer, and the parallel computing efficiency is 90\%. The new method can be used for the large-scale parallel calculation for LES simulation of the turbulent wind field. The results show that there is a striped pre-order structure near the wall in the transient velocity distribution. The velocity distribution of the average field conforms to the logarithmic law, and the turbulence characteristic of the wind field is basically reasonable.