Influence of dilatation structures on particle transport in compressible turbulent channel flows

The influence of dilatation structures on particle transport in supersonic channel turbulence is investigated by direct numerical simulation with nominal Mach number Ma=4.7, and friction Reynolds number Reτ=859. Eulerian-Lagrangian point-particle approach is employed for tracking the particles with nominal Stokes numbers St0+=1∼1000. We find that the dilatation structures are primarily localized in near-wall low-speed streaks, with a stable convective velocity of approximately 34uτ. Expansion regions (θ′>0) induce off-wall fluid motion and positive wall-normal acceleration of particles, while compression regions (θ′<0) cause toward-wall fluid motion and negative particle wall-normal acceleration. Large-inertia particles (St0+=200) respond weakly to the dilatation structures, whereas small-inertia particles (St0+=1) exhibit rapid responses with downstream-shifted acceleration and velocity distributions. Dilatation structures exert a subdominant influence on particle transport relative to the sweep and ejection events, with their induced particle transport being approximately 1/3 that of the latter and particle wall-normal transport distances less than one viscous scale. This limited effect of dilatation structures arises from short interaction time during which particles go through dilatation structures rapidly due to the streamwise velocity differences between the particles and the structures, as well as cancelation by adjacent structures with opposite fluid motions.