Experimental Study Of The Drag Forces On Hollow Blocks

Whenever there is relative motion between a solid body and the fluid in which it is immersed, the body experiences a net force, due to the action of the fluid. The result force can be resolved into components parallel and perpendicular to the direction of flow, the drag and lift forces correspondingly. The drag forces are the major forces that make the object move in the horizontal direction. When there are hollow structures in the block, the drag forces will be changed because the weight becomes lighter. In the dissertation, the research subjects are the hollow blocks with different porosity. The drag forces acting on the hollow cubic block and the square-section cylinder are surveyed in the variable slope flume.The study shows that the total drags acting on a hollow block are affected by the porosity in the same flow condition , that is, the bigger the porosity is, the smaller the drag force is. By inducting concepts of the porosity and the equivalent particle size, this dissertation puts forward the formula for the drag force calculation, considering the effect of porosity.The angles between the normal line direction and the flow direction shows strong effect to the drag forces in the study, this dissertation puts forward a formula about interference factor of the angles. It indicates that the bigger the angle is, the bigger the drag force is, under the condition of the cubic blocks. Meanwhile, the drag force coefficients change with the angle. The drag force coefficients get the smallest value when the angle is 20° ,the projective area becomes larger at the same time, so the drag forces show a growing tendency.