Velocity difference changes between fluid and sand particles in boundary-layer and very near wake area

Abstract

Fluent simulates the water-sand flow around a cylinder. Monitoring lines are set up at different positions in the cylindrical surface and the very near wake area behind the cylinder, in order to explore the speed difference of fluid and sand in the water-sand two-phase flow in the boundary-layer and the very near wake area. The results show that the sand particles stay for the longest time on the back of the cylindrical surface and in the very near wake area, and a small part of the sand particles are sticky on the back of the cylindrical pier. When the height of the cylinder is z/D ? (1.57, 3.14), the turbulent flow on the cylindrical surface is fully developed. The dynamic pressure of the flow field in the very near wake area be-hind the cylinder fluctuates greatly, and the water-sand flow is extremely unstable. At the monitoring position of the cylinder, there is a sudden decrease in the velocity of the fluid, while the velocity of the sand particles changes little and remains finally at about -0.02 m/s. The water-sand flow field near the wall changes drastically, but the velocity change of sand particles has obvious hysteresis compared with fluid. When leaving the near-wall position but still in the cylindrical wake area (x/D ? 3), the changes in the water-sand flow field are more intense and the velocity of the sand particles is still slightly larger than the fluid velocity.