壁湍流调制雷诺应力和拟序结构应变率空间形态的层析PIV实验研究

采用高时间分辨率的层析PIV技术,测量了水洞壁湍流三维速度分量空间分布的时间序列,应用局部平均速度结构函数概念对流向速度信号进行多尺度分解,以流向速度分量的局部平均速度结构函数过零点作为特征量检测壁湍流中拟序结构猝发的喷射和扫掠过程,应用空间相位平均技术提取拟序结构猝发的喷射和扫掠过程各速度分量、涡量分量、拟序结构速度应变率分量以及调制雷诺应力分量的空间相位平均拓扑形态.为了引入平衡态涡粘模型假设模拟调制雷诺应力,研究了拟序结构猝发过程中调制雷诺应力分量和速度变形率分量的空间分布形态,发现两者之间的空间相位分布不一致.由于存在时空相位不同步性,说明需要考虑大尺度拟序涡结构引起动量传递的时空弛豫效应.应用经典的线性平衡态下的Boussinesq涡粘模型不能准确地描述壁湍流拟序结构动量传递非平衡现象的物理机理.对于壁湍流拟序结构动力学方程中调制雷诺应力的模拟,应采用包含时空相位信息的复涡粘张量模型.由于雷诺应力与速度变形率的时空不同步性,对非平衡非局部湍流场的数值模拟提出了一个挑战性的问题,建议采用包含相位信息的复涡粘张量模型来模拟雷诺应力张量,从而更加符合雷诺应力演化的物理机理,这一模型有可能成为一个很有发展前景的封闭模型,从而更加准确地预测工业领域中广泛存在的非平衡湍流.

Tomographic PIV experimental investigation of topological modes of modulated Reynolds stress and velocity strain rate for coherent structure

The 3D-3C velocity fields of the wall-bounded turbulence in water tunnel were measured by time-resolved tomographic PIV.The concept of multi-scale spatial locally averaged velocity structure function was introduced to perform the multi-scale decompositions of longitudinal velocity component.The ejection and sweep events of coherent structure burst were deduced by the index of zero-crossing of multi-scale spatial locally averaged streamwise velocity structure function.The spatial phase-averaged topological modes of velocity,vorticity,modulated Reynolds stress and velocity strain rate for ejection and sweep events of coherent structure burst are obtained by spatial phase-averaged technique.In order to introduce eddy viscosity model to simulate the modulated Reynolds stress,spatial distribution modes of modulated Reynolds stress and velocity strain rate are compared and the spatial phase difference between them are found to be distinct.Due to the nonsynchronization of the temp-spatial phase,it is necessary to consider the relaxation effects of the momentum transferring caused by the large-scale coherent vortex structures. Therefore,the classical linear equilibrium under the Boussinesq eddy viscosity hypothesis can not describe the physical mechanism of non-equilibrium momentum transfer for coherent structures in wall-bounded turbulence.In order to simulate the modulated Reynolds stress in coherent structures dynamics properly,the complex eddy viscosity tensor model with temp-spatial phase information should be employed.Because of the temp-spatial nonsynchronization between the modulated Reynolds stress and velocity strain rate,the numerical simulation of non-equilibrium non-local turbulence is becoming a challenging problem.The present proposed complex eddy viscosity tensor model with temp-spatial phase information should be employed to reveal the physical evolution mechanism of the modulated Reynolds stress.It may become a promising model to enclose Reynolds stress and forecast the widespread industrial non-equilibrium turbulence more accurately.