Hybrid spatially-evolving DNS model of flow past a sphere
Hybrid spatially-evolving DNS model of flow past a sphere
复制标题
流经球体的混合空间演化 DNS 模型
DOI：
10.1016/j.compfluid.2018.05.018
复制
发表时间：
2018
影响因子：
2.8
通讯作者：
S. Sarkar
中科院分区：
文献类型：
--
作者：
A. VanDine;K. Chongsiripinyo;S. Sarkar
采用混合空间演化模型的直接数值模拟方法，模拟了亚临界雷诺数Re=U∞D/ν=3700时拖曳球体后的湍流尾迹，其中U∞为自由流速度，D为球体直径，ν为粘性。球体不在模型域中，但真实的流入条件是从包含实体的模拟中获得的。因此，该模型是包含主体和排除主体的模拟的混合体，极大地降低了计算成本，并允许对尾迹动力学进行下游研究。从流方向上的x1，即x1/D=3、6和10三个位置提取入口条件，以考察结果对提取位置的敏感性。对弗劳德数为Fr=U∞/ND=∞，3和1的未分层流体和分层流体进行了模拟，其中N是背景的浮力频率，以探索不同层化水平下模型的有效性。研究发现，为了准确地捕捉流体的物理特性，需要对提取位置进行战略性选择。模拟结果表明，在提取位置x1/D=3处，混合模式模拟的平均尾迹衰减与包含身体模拟的结果一致。分层尾迹的分层流动结构被很好地捕捉到，而涡度等值线上清晰地观察到了指示内波传播的相线，这与包含物体的模拟结果是一致的。在所有情况下都注意到了准确的湍流动能(TKE)捕获。采用更高分辨率的网格进行了额外的模拟，并进行了分析，以展示网格分辨率对湍流统计的影响。对TKE预算项的检查表明，改进的网格分辨率与进水口附近的包括身体的模拟结果更好地吻合，在那里混合模拟和包括身体的模拟之间的分辨率差异最大。结果表明，该混合模型是研究湍流尾迹动力学的一种可靠工具。
Direct numerical simulation in the form of a hybrid spatially-evolving model is used to simulate the turbulent wake behind a towed sphere at a subcritical Reynolds number, R e= U∞ D/ν= 3700, where U∞ is the free stream velocity, D is the diameter of the sphere, and ν is the viscosity. The sphere is not present in the model domain but realistic inflow conditions are obtained from a body-inclusive simulation. As such, the model is a hybrid of both body-inclusive and body-exclusive simulations which greatly reduces computational cost and allows for downstream study of wake dynamics. Inlet conditions are extracted from three locations in the streamwise, x 1, direction namely x 1/D= 3, 6, and 10, to investigate the sensitivity of the results to extraction position. Simulations are performed considering both unstratified and stratified fluids with Froude numbers, F r= U∞/N D=∞, 3, and 1 where N is the buoyancy frequency of the background, to explore the model effectiveness for varying levels of stratification. It is found that a strategic choice in extraction location is required in order to accurately capture the flow physics. Simulation results show less agreement with the body-inclusive simulations at extraction location x 1/D= 3 than with x 1/D= 6 or x 1/D= 10. Mean wake decay of the hybrid model simulations is consistent with the body-inclusive simulations. The layered flow structure of the stratified wake is captured well while phase lines indicating internal wave propagation are clearly observed in vorticity contours and are consistent with the body-inclusive simulations. Accurate turbulent kinetic energy (tke) capture is noted for all cases. Additional simulations with higher resolution grids were performed and analyzed to demonstrate the impact of grid resolution on turbulence statistics. Examination of tke budget terms indicates that improved grid resolution results in better agreement with the body-inclusive simulation near the inlet where the resolution disparity between the hybrid and body-inclusive simulations is most significant. The hybrid model is shown to be a robust tool for the study of turbulent wake dynamics.