Experimental Studies On The Sand Accumulation Phenomenon In Flow Around A Circular Cylinder Near To A Plane Wall

Flow around a circular cylinder near to a plane wall has been a subject of research due to its practical and physical importance. Because of the effect of the wall, the wall boundary layer is dominant, which makes the vortex shedding in wake different from those on flow around an isolated circular cylinder. Simultaneity flow in wall boundary layer is seriously affected because of the cylindrical existence. Because of this complexity and practical use, there still many scholar pay a lot of interest in studying this problem.When carrying on experiments of the flow past a circular cylinder near to a plane wall using Particle Image Velocimetry(PIV),the sand accumulation line is found on the plane wall downstream of the cylinder. This phenomenon refers to the characteristics of velocity distribution and vortex structures in the wake of flow around a circular cylinder near to a plane wall. In order to have a further understanding of the process that forming the sand accumulation line and the relationship between sand accumulating and the interaction of the boundary layer and the wake, we have conducted a very particular experiments.The circular cylinders, having two different diameters, are set in a fully developed turbulent boundary layer, and the particles seeded in the water can follow the flow very well. Under two Reynolds numbers of momentum loss thickness with 12 gap ratios from 0 to 1.5, the velocity vector distribution and the data of the sand accumulation lines are obtained.Analyzing the velocity distribution and the vortex structure of the ensemble average flow field and the transient flow field and observing the process forming sand accumulation line indicate that the separation take places due to the interaction of the wake cylinder and the boundary layer of the plane wall. There are relatively stable separate zone and wall attached vortex in the periodic wake flows. The speed of particles entrained by flow reduced and deposes there. Some characteristics of the vortex structure that in the wake of cylinder near to a plane wall can be learned by the appearance of the sand accumulation lines.