Amir Esteghamatian (Johns Hopkins University) - Particle-laden viscoelastic turbulence in channel flow

In this talk, we examine the competing effects of particles and viscoelasticity in a turbulent channel flow. Individually, viscoelasticity and particles can appreciably modify channel-flow turbulence: The addition of polymers can quench the turbulent shear stress, making them attractive drag-reducing agents. In contrast, finite-size particles can increase the turbulent drag. When both viscoelasticity and the particle phase are present, the dynamics become much more intriguing as we demonstrate using direct numerical simulations of neutrally buoyant particles in a viscoelastic turbulent channel. Unlike the single-phase cases, the particle-laden flows undergo a drag enhancement with increasing viscoelasticity above a certain Weissenberg number. This effect is due to a drastic increase in polymer stresses near the surfaces of particles. Next, we explore the settling effect of particles in Newtonian and viscoelastic channel flows. We show that even a slight density mismatch has various implications in the dynamics of particles and fluid, from changes in mean quantities at a global scale to clustering and lateral forces acting on individual particles.