Particle stresses in dilute, polydisperse, two-way coupled turbulent flows.

Direct numerical simulations are performed of turbulent planar Couette flow which are seeded with two-way coupled particles at low volume concentration. Based on an understanding of the development of particle stress (horizontal momentum carried vertically on average by the particle phase) in monodisperse systems at various particle Stokes numbers, several bidisperse and continuously polydisperse systems are simulated which are chosen to understand how flows containing blends of particle Stokes numbers can be effectively modeled in the dilute regime. Under noninteracting conditions, the particle stresses from particles with different inertia and different feedback stresses are shown to be linearly additive, providing a convenient method for effectively representing dispersed phase stress in polydisperse systems. While this is true, it is demonstrated that a single effective particle size is in general not sufficient at representing the entire mixture.