Detached eddy simulations and particle lagrangian tracking of horizontal rough wall turbulent channel flow

Numerical simulations are performed to investigate the influence of wall roughness on the dispersed-phase properties of particle-laden turbulent channel flow. Predictions are assessed against the experimental measurements of Sommerfeld and Kussin (Wall roughness effects on pneumatic conveying of spherical particles in a narrow horizontal channel, Powder Tech. 142 (2004), pp. 180-192). The carrier flow is modeled using Spalart-Allmaras-based detached eddy simulation at a Reynolds number Reτ, based on the friction velocity and channel half width, of 1035. The particulate phase motion is modeled using Lagrangian tracking with particles experiencing the drag force and gravitational settling. Influences of inelastic, interparticle collisions are treated using a deterministic approach. The effects of wall roughness are modeled using two stochastic approaches, specifically, the "shadow effect model" and the "multi-wall collision model", the latter accounting for the effects of multiple rebounds unlike the former. The simulations show in general good agreement between DES predictions and measurements, and sensitivities of the dispersed-phase statistics to choice of the wall roughness model. In general, the shadow effect model leads to a less prominent effect of wall roughness compared to predictions obtained using the multi-wall collision model. Analysis of the probability density function of the particle rebound angles shows that the shadow effect model exhibits a substantially higher probability to generate grazing particle motion following rebound, different from the multi-wall collision model and measurements. Discrepancies between some statistics and measurements are attributed to rebound coefficients in the models that require further investigation.