(116a) Effect of Roughness on Particle Laden Turbulent Channel Flow

Particle-laden turbulent flows find applications for a wide range of industrial processes like pneumatic conveying, fluidized beds, etc., The majority of the processes use particles with high inertia. It has been previously observed that with an increase in particle loading, turbulence intensity decreases, and beyond a specific volume fraction, there is a drastic collapse of fluid turbulence. The earlier studies considered the particle-particle and particle-wall collisions to be elastic and surfaces are smooth. Here, we consider the effect of rotating particle collision with other particle and the wall on the fluid phase turbulence attenuation. Point-particle Direct numerical simulation (PP-DNS) is used for turbulent air and particle suspension in a rectangular channel of different roughness. The Reynolds number based on the channel width and average air flow velocity and viscosity Re = 5600 is considered. The particle Reynolds number based on the particle diameter and root mean square of the difference in the particle and fluid velocities is of the order O(1). The particle volume fraction is small, in the range of 0–3.5 × 10^-3 and the particle Stokes number (ratio of particle Stokes relaxation time and fluid integral time) is 200. It is observed that irrespective of any type of the roughness between particle-particle interactions it is the roughness between particle-wall interaction that controls the complete dynamics of the system by making the mean fluid velocity depicting more like a plug flow, reducing the turbulent intensity near the wall but increasing it elsewhere in the channel thus increasing the overall turbulent quantities, reducing the particle mean velocity whereas increasing the particle translation and angular velocity fluctuations throughout the channel as the roughness between particle-wall interactions increase. Figure 1 shows significant difference in turbulent quantity for with and without particle-wall roughness factor. Further an early collapse of fluid turbulence intensity is observed when the particle and walls are rough compared to the smooth interactions. The effects of reverse torque on the fluid by the particles is negligible and does not affect the results which shows that reverse drag force is the prominent factor deciding how particle effects the fluid.