A large eddy simulation of turbulent particle-laden flow inside a cubical differentially heated cavity

Abstract

Large Eddy Simulations (LES) have been conducted to investigate turbulent air flow and particulate depletion inside a cubical cavity of length 0.7m and temperature difference of 39K between the hot and cold opposing vertical walls, thus resulting in a Rayleigh number of 109. Initial confrontation of the idealized flow field against experimental data (Kalilainen, Rantanen, Lind, Auvinen, & Dehbi, 2016) revealed that wall to wall radiation needs to be taken into account in order to reproduce the enhanced turbulence levels and reduced thermal stratification observed in the experiment. We introduce thereafter radiation effects indirectly by specifying measured temperatures rather than zero convective heat flux on the adiabatic walls.The LES predictions with realistic boundary conditions are in very good overall agreement with the measured velocity fields and temperature profiles. This accurate flow field is used to perform Lagrangian tracking simulations for spherical SiO2 particles with aerodynamic diameters of 1.4μm and 3.5μm. Here too, the computed particle depletion rates are in excellent agreement with the experimental data. Further Euler/Lagrange simulations are conducted for particles with hypothetical diameters in the range of 0.5μm to 10μm. Particles with diameters larger than 3 μm are removed at rates comparable to those predicted by the simple “stirred settling” model. However, as particle diameters decrease, the deposition rates are increasingly faster than predicted by stirred settling, and the decay constants tend towards an asymptotic value that is independent of particle size. Additionally, sensitivity computations show that thermophoresis has little effect on the removal rates of particles, but the inclusion of the thermophoretic force modifies the deposition pattern of sub-micron aerosols. The strong turbulent diffusion is thus the overriding cause for the significant deposition rates of smaller particles.