On the turbophoresis of small inertial particles and implications for particle-laden wall-modeled large-eddy simulations

In a turbulent shear flows, gradients in turbulence intensity drive a net migration of small, heavy inertial particles toward regions of lower turbulence intensity. This phenomenon, known as turbophoresis, causes particles to preferentially accumulate in the near-wall region of wall-bounded turbulent flows. Simulating high Reynolds number wall-bounded flows requires an approach that does not resolve near-wall dynamics, such as wall-modeled large-eddy simulations (WMLES). At first glance, WMLES may seem ill-suited for accurately simulating turbophoresis, given that coherent structures in the viscous and buffer layers are completely unresolved. In this talk, I will examine the role of near-wall coherent structures on particle transport and demonstrate effect of Stokes number on WMLES of particle-laden flows. The biased sampling of low-speed streaks is very important for low and moderate Stokes numbers (based on wall friction units) but may be neglected for higher Stokes numbers. This means that accurate prediction of particle concentration profiles with WMLES is significantly easier at higher Stokes numbers. At low Stokes numbers, models for the fluid velocity seen by the particles must account for the complex spatio-temporal coherence of near-wall fluctuations.