惯性颗粒和壁湍流的相互作用:湍流调制及颗粒分布

Interactions between inertial particles and wall-bounded turbulence:Turbulence modulation and particle distribution

直接数值模拟壁面湍流与惯性点粒子方法被用来研究粒子对湍流的调制机理以及粒子在湍流场中的分布。由于在壁面湍流中,内层(约为y+<100,y+为黏性尺度下的壁面垂直方向坐标)与外层(约为y+> 100)中存在着两种特征结构,即内层中的大尺度结构(large-scale structures, LSMs)与外层中的超大尺度结构(very-large-scale structures, VLSMs),这两种特征结构控制着壁面湍流的动力学过程。因此研究方向主要是探究粒子与LSMs以及VLSMs之间的相互作用:即通过研究粒子惯性效应对LSMs主导的湍流内层自维持过程来解释不同惯性的粒子导致湍流增强或减弱的原因;通过研究粒子惯性效应对VLSMs主导的湍流外层的调制,提出粒子的惯性效应导致VLSMs增强的直接与间接机理。同时,通过人为控制LSMs和VLSMs与粒子分别耦合来研究这两种特征结构的存在导致的粒子聚集与群聚行为。最后,推导了惯性粒子沉积速度的控制方程,用于分析控制粒子沉积速度的关键因素。

Direct numerical simulation of wall-bounded turbulent flows laden with inertial pointwiseparticles is used to investigate the turbulence modulation and particle distribution.In wall-bounded turbulence,two characteristic structures,i.e.,large-scale motions(LSMs)and very-large-scale motions(VLSMs),dominate the flow dynamics in the turbulent inner(y+<100)and outer layers(y+>100)respectively.Thus,we focus on particles interaction with LSMs and VLSMs.In the inner layer,we investigate the particles modulation of the regeneration cycle to explain the turbulence enhancement and attenuation due to particle inertia.In the outer layer,we find two mechanisms for VLSMs enhancement due to particle inertia.Low-inertia particles promote VLSMs indirectly through the enhancement of the regeneration cycle(the self-sustaining mechanism of LSMs)in the inner region,whereas high-inertia particles enhance VLSMs directly through contribution to the Reynolds shear stress at similar temporal scales in the outer region.Meanwhile,particles preferential accumulation and clustering behavior in LSMs and VLSMs are analyzed.Finally,we derive the transport equation for particle setting velocity which allows us to identify the distinct mechanisms governing the particle settling in wallbounded turbulence.