Dynamics of particle-laden turbulent suspensions: Effect of particle roughness

The Fluctuating Force Fluctuating Torque (F3T) model is developed and evaluated for the dynamics of a turbulent particle-gas suspension of rough spherical particles in a turbulent Couette flow in the limit where the viscous relaxation time of the particles and the time between collisions are much larger than the integral time for the fluid turbulence. The fluid force/torque exerted on the particles comprises a steady part due to the difference in the particle velocity/angular velocity and the fluid mean velocity/rotation rate, and a fluctuating part due to the turbulent velocity/vorticity fluctuations. The fluctuations are modeled as Gaussian white noise whose variance is determined from the fluid velocity and vorticity fluctuations. The smooth and rough inelastic collision models are considered for particle-particle and particle-wall collisions. The results show that inclusion of roughness is important for accurately predicting the particle dynamics; the second moments of the velocity fluctuations for rough particles are higher than those for smooth particles by a factor of 2-10, while the second moments of the angular velocity fluctuations are higher by 1-2 orders of magnitude. The F3T model quantitatively predicts the number density, mean and root-mean-square velocity and angular velocity profiles, and the distribution functions for the particle velocity and angular velocity, even though a Gaussian model is used for the highly non-Gaussian distributions for the force and torque fluctuations.