中文摘要：

为了研究自由剪切流动中颗粒扩散的统计特性，对空间发展模式的三维气固两相射流和时间发展模式的三维气固两相混合层进行了直接数值模拟。其中对气相不可压缩Navier-Stokes方程的求解分别采用有限容积方法和拟谱方法，对离散惯性颗粒的跟踪采用单向耦合的拉格朗日方法。统计结果显示，当流场进入自相似状态后，以流场速度梯度二阶不变量Q为自变量的颗粒数的概率分布函数也呈现出与颗粒尺寸和时间发展无关的自相似特性。

英文摘要：

To investigate the statistical property of particle dispersion in free shear flows, a three-dimensional spatially-developing particle-laden jet and a three-dimensional temporally-developing particle-laden mixing layer are studied by means of direct numerical simulation （DNS）. The incompressible Navier-Stokes equations are solved using finite volume method and pseudo-spectral method, respectively. The dispersed inertial particles are traced in the Lagrangian framework based on one-way coupling. The statistical results show that the probability distribution of particle number, which is a function of the second invariant of velocity gradient tensor Q, becomes self-similar, i.e. size-independent and time-independent when the flows reach self-similar status.