Abstract:
Direct numerical simulation of wall-bounded turbulent flows laden with inertial pointwise-particles is used to investigate the turbulence modulation and particle distribution. In wall-bounded turbulence, two characteristic structures, i.e., large-scale motions (LSMs) and very-large-scale motions (VLSMs), dominate the flow dynamics in the turbulent inner (
y+ < 100) and outer layers (
y+ > 100) respectively. Thus, we focus on particles interaction with LSMs and VLSMs. In the inner layer, we investigate the particles modulation of the regeneration cycle to explain the turbulence enhancement and attenuation due to particle inertia. In the outer layer, we find two mechanisms for VLSMs enhancement due to particle inertia. Low-inertia particles promote VLSMs indirectly through the enhancement of the regeneration cycle (the self-sustaining mechanism of LSMs) in the inner region, whereas high-inertia particles enhance VLSMs directly through contribution to the Reynolds shear stress at similar temporal scales in the outer region. Meanwhile, particles preferential accumulation and clustering behavior in LSMs and VLSMs are analyzed. Finally, we derive the transport equation for particle setting velocity which allows us to identify the distinct mechanisms governing the particle settling in wall-bounded turbulence.