基于变分模态分解的壁湍流拟序结构形态研究

应用多分量准二维变分模态分解技术,对直接数值模拟的湍流边界层的流向-法向平面进行了分解。通过对从低雷诺数到中等雷诺数(Reτ=400~1750)各个工况的瞬时流场的观察,定性地得到了不同模态所对应的物理结构特征。通过两点相关云图形态和倾斜角度的比较,定量地对比了不同模态对应的拟序结构倾角随法向高度的变化。一阶模态主要对应大尺度扫掠/喷射事件,第二阶模态则对应近壁流向涡结构。两阶模态的拟序结构倾角随法向高度的变化趋势与雷诺数呈弱相关,表明大小尺度模态的几何特征在所研究的雷诺数范围内存在自相似性。

Morphological analysis of coherent structures in wall-bounded turbulence based on variational mode decomposition

The multi-component quasi-bivariate variational mode decomposition technique is applied to decompose the turbulent boundary layer velocity field acquired by direct numerical simulation.By observing the instantaneous flow field at various cases from low to medium Reynolds number(Reτ=400~1750),the characteristics of the coherent structures corresponding to different modes are qualitatively obtained.By comparing the morphology and inclination angle of the two-point correlation map,the variation of the inclination angle of the coherent structure corresponding to different modes with the normal height is quantitatively compared.The first mode mainly corresponds to large-scale sweep/ejection events, while the second mode corresponds to near-wall streamwise vortex structures.The variation trend of the inclination angle of the coherent structure of the modes with the normal height is weakly dependent on Reynolds number,which indicates that the geometric characteristics of large and small scale structures follow certain similarity within the Reynolds number range studied.