Impact of Particle Injection Velocity on the Stability of the Particulate Rayleigh-B\'enard System

Abstract

The linear stability of a thermally stratified fluid layer between horizontal walls, where thermal particles are continuously injected at one boundary and extracted at the other - a system known as particulate Rayleigh-B\'enard (pRB) - is studied. For a fixed volumetric particle flux, reducing the injection velocity stabilizes the system when heavy particles are introduced from above, but destabilizes it when light particles are injected from below. For very light particles (bubbles), low injection velocities can shift the onset of convection to negative Rayleigh numbers, i.e. heating from above. Particles accumulate non-uniformly near the extraction wall and in regions of strong vertical flow, aligning with either wall-impinging or wall-detaching zones depending on whether injection is at sub- or super-terminal velocity.