Experimental study on the effects of particle-wall interactions on VLSM in sand-laden flows

The interaction between heavy particles with high Stokes number () and the wall, known as the particle-wall (P-W) process, widely exists in natural and engineering two-phase flows, whereas its effects on particle-laden flows and the large-scale/very large-scale turbulent motions (VLSM) remain unclear. In this paper, two types of wind-blown sand-laden flows were experimentally designed and investigated by keeping the same free stream velocity, flow Reynolds number and particle number. In the first type, sand particles were directly blown from a sand bed at the bottom wall of the wind tunnel, and the P-W process occurred in the whole wall-normal region of the sand-laden flow. In the second type, sand particles were released from a feeder at the top wall of wind tunnel, and the P-W process was only present in a lower wall-normal region. Simultaneous two-phase particle image/tracking velocimetry measurements were conducted for uncovering the characteristics of turbulent structures in the particle-laden turbulent boundary layers. The results confirmed that the VLSM with streamwise scales exceeding ( is boundary layer thickness) above a certain height exist in both types of the sand-laden flows and could be significantly affected by the P-W process. That is, in the region without the P-W process, the presence of sand particles can enlarge the VLSM, while in the region with the P-W process, the VLSM are substantially reduced in size or even destroyed. The reduction degree is found to be closely related to the strength of the P-W process.

Automated summary

This study investigates the influence of the interaction between heavy particles (high Stokes number) and the wall on two-phase flows and large-scale turbulent structures. Experimental results confirm that the P-W process significantly affects the size and strength of VLSM.