| 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. In the dissertation, the drag forces acting on the square-section cylinder are surveyed in the flume, and attention is pay to the two factors:(1) The effect of cylinder shape to the drag force. The total drag acting on a body is comprised of two componentss kin-friction drag and pressure drag. Either skin-friction drag or pressure drag may predominate depending on the shape. This dissertation studies the variety relation of the drag and the cylinder shape, and then puts forward the formula for the drag force calculation, considering the effect of shape.(2) The interference of two cylindes in tandem arrangement in water. In water the cylinder of drag forces influence by the distance between two square-section cylinders in tandem arrangement. In this dissertation the cube is on behalf of the block body and interference factors and max-distance of the influence is Defined. The max-distance and relative max-distance of the influence is been studied initially. The relation of drag force and the distance between two cubes in tandem arrangement is researched. The relation of interference factors and relative diatance between two cubes in tandem arrangement is researched, so as to put forward a formula about interference factors of the behind cube and relative diatance between two same size-cubes.
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