On the motion of small particles in a homogeneous isotropic turbulent flow

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Abstract
The motion of small spherical solid particles are simulated numerically in a decaying homogeneous isotropic turbulent gas flow field generated by the large eddy simulation. By comparing with the previous experimental and theoretical studies, the present method is found to be a successful tool to generate the properties of the particle motion involving the second‐order statistics, such as the mean‐square displacement, the dispersion coefficient, and the root‐mean‐square velocity fluctuation. The present results are complementary to the experimental data and include a detailed study of the effects of the flow turbulence, the particle’s inertia, and the particle’s free‐fall velocity in a still fluid on the particle dispersion and turbulence intensity. By performing particle simulation in the flow fields generated with different values of the coefficient in the subgrid model and with different sizes of the calculation domain, it is found that the particle motion is indeed controlled mainly by the large eddies, and there are only minor contributions of the high wave number components of the flow field to the particle motion. Also included in the results is the effect of the turbulence decay on the long time particle dispersion. It is found that the peak value of the dispersion coefficient during the turbulence decay can be correlated with the large‐scale Reynolds number and the velocity ratio between the particle’s free‐fall velocity and the root‐mean‐square velocity fluctuation of the fluid. Simulation also shows that the particle’s settling velocity in turbulence is greater than that in a still fluid.