The interaction between the finite-size particles and stably stratified turbulent channel flow.

The interaction between finite-size particles and stably stratified turbulent channel flow was investigated using direct numerical simulation. The parameters of the fluid flow have been chosen as $Pr=7$, $Re_\tau=180$ and $Ri_\tau=0$ or $20$. The properties of the solid particles are such that the density ratio $1.00098$ or $1$, and they have an adiabatic surface. The diameter of the particle is $D_p^{+}=37.8$. The stratification is known to interfere with the transfer of heat and momentum in the vertical direction. The particles become trapped between the wall and the center of the channel because of the internal gravity wave (IGW) formed by the buoyancy. Because of this IGW, which acts as a wall, the particles have a locally low concentration in the channel center. This stratification effect is further enhanced by particles as the volume fraction of the particles increases, and the enhanced stratification again has a stronger influence on the distribution of the particles. Near the wall, the particles experience primarily high-speed streak regions. We present statistical descriptions for this interaction, namely the residence time, the PDF of the particle velocity and so on.