Particle Motion in the Linear Shear Duct Flow

Abstract

The present study is concerned with particle motion in the linear shear flows with constant velocity gradient in a duct. Effects of the velocity gradients at a high Reynolds number on lift acted on a spherical particle are investigated by photographing trajectories of particles suspending in the shear flows using a high speed video and numerical simulation of particle distribution in the duct using the method of Direct Simulation Monte Carlo. The Reynolds number (relative air velocity×particle diameter/kinematic viscosity of air) is ranging from 950 to 2700. The characteristics of the duct flows are discussed after measuring the velocity, and turbulence intensity, or auto-correlation and cross-correlation using hot-wire anemometer and FFT digital spectrum analyzer in order to make clear that the test duct is suitable to the experiments. In the numerical simulation by DSMC the particle-particle and particle-duct wall collisions are taken into account. From the results of numerical simulation, it is shown that particles move from the higher velocity side to the lower velocity side of the shear flows, and this result agrees with the high speed video picture of particle trajectories in the near part downstream of the particle supply part. But, in the far part, particles are scattered randomly due to the particle collisions. In conclusion, It is made clear that lift is applied on a sphere from the higher velocity side to the lower velocity side on the linear shear flows at high Reynolds number.The present study is concerned with particle motion in the linear shear flows with constant velocity gradient in a duct. Effects of the velocity gradients at a high Reynolds number on lift acted on a spherical particle are investigated by photographing trajectories of particles suspending in the shear flows using a high speed video and numerical simulation of particle distribution in the duct using the method of Direct Simulation Monte Carlo. The Reynolds number (relative air velocity×particle diameter/kinematic viscosity of air) is ranging from 950 to 2700. The characteristics of the duct flows are discussed after measuring the velocity, and turbulence intensity, or auto-correlation and cross-correlation using hot-wire anemometer and FFT digital spectrum analyzer in order to make clear that the test duct is suitable to the experiments. In the numerical simulation by DSMC the particle-particle and particle-duct wall collisions are taken into account. From the results of numerical simulation, it is shown that particles move from the higher velocity side to the lower velocity side of the shear flows, and this result agrees with the high speed video picture of particle trajectories in the near part downstream of the particle supply part. But, in the far part, particles are scattered randomly due to the particle collisions. In conclusion, It is made clear that lift is applied on a sphere from the higher velocity side to the lower velocity side on the linear shear flows at high Reynolds number.