Experimental Investigation of the Wall-Effect on a Cylindrical Obstacle Moving in a Viscous Fluid at Low Reynolds Numbers

The force and moment acting on a cylindrical obstacle moving in a viscous fluid bounded by two parallel plane walls are investigated experimentally at Reynolds numbers ranging from 10 -1 to 10 -5 . The important points resulting from the experiments are that (1) the drag and the lift coefficients are exactly proportional to the reciprocal of the Reynolds number for a fixed wall distance; (2) the minimum drag is obtained when the obstacle is located halfway between the walls and the central line between the two walls; (3) the minimum lift is obtained when the obstacle is located on the central line between the two walls; (4) when δ (the distance of the obstacle from a wall) is small, a small change in the incidence produces a large change in the movement of the center of pressure; (5) for a fixed incidence, the center of pressure moves forward first, then moves backward as δ is increased; (6) the streamline pattern is unaltered even if the direction of motion is reversed.