在简单随机流场中搜索随机不相关粒子运动（RUM）
In search of random uncorrelated particle motion (RUM) in a simple random flow field
摘要：
对各向同性均匀湍流中分散颗粒运动的DNS研究[1]揭示了存在依赖于颗粒惯性τp（归一化颗粒响应时间或Stoke数）的随机不相关运动（RUM）分量。本文报道了在一个简单的线性随机平稳变化的流场的反向旋转涡的两个粒子的速度相关性作为一个功能的空间分离测量RUM的存在。用Stokes数表示，粒子在一个方向上的运动对应于重阻尼（τp < 0.25）或轻阻尼（τp > 0.25）谐振子。在轻微阻尼的情况下，粒子越过流动的滞流线，从一个涡投射到另一个涡（所谓的弹弓效应）。结果表明，RUM仅在τp > 0.25时出现，并随Stokes数的增加而单调增加.粒子对分离分布函数的计算表明，粒子浓度场从未达到平衡，零分离浓度随时间单调增加。这与粒子速度场的平均Liapounov指数（有限可压缩性）的计算负值是一致的。
英文摘要：
DNS studies of dispersed particle motion in isotropic homogeneous turbulence [1] have revealed the existence of a component of random uncorrelated motion (RUM)dependent on the particle inertia τp(normalised particle response time or Stoke number). This paper reports the presence of RUM in a simple linear random smoothly varying flow field of counter rotating vortices where the two-particle velocity correlation was measured as a function of spatial separation. Values of the correlation less than one for zero separation indicated the presence of RUM. In terms of Stokes number, the motion of the particles in one direction corresponds to either a heavily damped (τp < 0.25) or lightly damped (τp > 0.25)harmonic oscillator. In the lightly damped case the particles overshoot the stagnation lines of the flow and are projected from one vortex to another (the so-called sling-shot effect). It is shown that RUM occurs only when τp > 0.25, increasing monotonically with increasing Stokes number. Calculations of the particle pair separation distribution function show that equilibrium of the particle concentration field is never reached, the concentration at zero separation increasing monotonically with time. This is consistent with the calculated negative values of the average Liapounov exponent (finite compressibility) of the particle velocity field.
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