旋流和无旋突扩流动的LES和RANS模拟

LES AND RANS MODELING OF SUDDEN EXPANSION FLOWS WITH AND WITHOUT SWIRL

本文用smagorinsky-Lilly亚网格尺度湍流模型对旋流突扩流动(s=0.53)和无旋突扩流动(s=0)进行了大涡模拟(LES模拟),同时分别用压力应变项为IPCM和IPCM+Wall模型的雷诺应力方程模型进行了RANS模拟,和LES的统计结果对比。LES的统计结果与雷诺应力模型的模拟结果及实验对照表明,LES结果与实验结果的吻合比雷诺应力模型的好,说明所用的亚网格尺度湍流模型对旋流流动是适用的,LES结果是可信的。LES的瞬态结果揭示出在旋流作用下,流场中存在复杂的旋涡脱落现象。大涡结构极易破碎成小涡,而在无旋突扩流动的情况下,由于剪切的作用更强,大涡结构的尺寸和范围比旋流流动的要大。

Sudden-expansion flows with swirl (s = 0.53) and without swirl (s = 0) are simulated by large-eddy simulation (LES) using a Smagorinsky-Lilly subgrid-scale model, and by RANS modeling using the Reynolds Stress equation model with the IPCM + wall and IPCM pressure-strain models. The LES statistical results and the RANS simulation results are verified by experiments. The former gives better agreement with the experimental results, indicating that the adopted subgrid-scale turbulence model is suitable for swirling flows and the LES results are reliable. The LES instantaneous results reveal the complex vortex shedding pattern in swirling flows. The initially formed large vortex structures soon break up in swirling flows. The size and range of large vortex structures in the sudden-expansion flow without swirl are much lager than those in the sudden-expansion flow with swirl because of stronger shear in non-swirling sudden-expansion flows.