Thermally Responsive Particles in Rayleigh-Bénard Convection

The effect of thermal inertia on the dynamics of particles with a thermal expansion coefficient larger than that of the fluid is investigated in Rayleigh-Bénard convection (RBC) using direct numerical simulations. A simple point-particles approach is used, where thermal expansion of both particles and fluid is included. These thermally responsive particles move towards the hot (bottom) or cold (top) plates, where they become lighter or heavier than the fluid to eventually escape this region of the flow. When the thermal response time of particles is large, this process is slow and particles spend more time at the walls than in the bulk. It is indeed shown that in this regime the number of particles at the plates is enhanced, compared to the uniform distribution found for tracer particles in RBC. A more complex point-particle approach, including non-linear effects on the drag forces, shows that non-linear thermal effects influence both the temperature and velocity statistics of the thermally responsive particles and cannot be ignored.