Influence of Reynolds number on the motion of settling, bidisperse inertial particles in turbulence
Influence of Reynolds number on the motion of settling, bidisperse inertial particles in turbulence
复制标题
雷诺数对湍流中沉降双分散惯性粒子运动的影响
作者：
M. Momenifar;R. Dhariwal;A. Bragg
利用直接数值模拟（DNS），研究了Taylor雷诺数$R_lambda$和Froude数$Fr$对各向同性湍流中双分散惯性颗粒沉降运动的影响。粒子的加速度在双分散粒子的相对运动中起着关键作用，我们发现，减少$Fr$导致的加速度的增强，但抑制其不稳定性。对于Stokes数$St>1$，由于沉降导致颗粒加速度受到较大范围的流尺度的影响，$R_lambda$对加速度的影响因重力而增强。粒子相对速度的概率密度函数（PDF）的结果表明，对于双分散粒子，降低$Fr$导致其在垂直（平行于重力）和水平方向上的相对速度的增强。重要的是，我们的研究结果表明，即使当颗粒沉降非常快，湍流继续发挥关键作用，在他们的垂直相对速度，并越来越多的R_lambda$增加。出现这种情况是因为，虽然沉降速度可能比湍流的典型速度大得多，但由于不稳定性，存在湍流对颗粒运动的贡献与重力沉降的贡献相同的流动区域。
Using Direct Numerical Simulations (DNS), we examine the effects of Taylor Reynolds number, $R_lambda$, and Froude number, $Fr$, on the motion of settling, bidisperse inertial particles in isotropic turbulence. Particle accelerations play a key role in the relative motion of bidisperse particles, and we find that reducing $Fr$ leads to an enhancement of the accelerations, but a suppression of their intermittency. For Stokes numbers $St>1$, the effect of $R_lambda$ on the accelerations is enhanced by gravity, since settling causes the particle accelerations to be affected by a larger range of flow scales. The results for the Probability Density Function (PDF) of the particle relative velocities show that for bidisperse particles, decreasing $Fr$ leads to an enhancement of their relative velocities in both the vertical (parallel to gravity) and horizontal directions. Importantly, our results show that even when the particles are settling very fast, turbulence continues to play a key role in their vertical relative velocities, and increasingly so as $R_lambda$ is increased. This occurs because although the settling velocity may be much larger than typical velocities of the turbulence, due to intermittency, there are significant regions of the flow where the turbulence contribution to the particle motion is of the same order as that from gravitational settling...