Forces on a near-wall circular cylinder

The pressure distribution around a near-wall smooth circular cylinder in cross-flow was mainly investigated. The experiment was conducted at the sub-critical Reynolds number ranging from 2.24·10⁴ to 8.94·10⁴, at which the regular vortex separation exists on an isolated circular cylinder. The experimental results indicate that the forces on a circular cylinder near a plane wall are different from those on an isolated circular cylinder. Drag and lift coefficients of a near-wall circular cylinder strongly depend on gap ratio. The increase of gap ratio results in the increase of drag coefficient and the declination of lift coefficient, drag coefficient ranges from 0.5 to 1.0, and lift coefficient from 0.25 to 0 when gap ratio gradually increases from 0 to 1.0, and then the forces tend to be nearly constant with the increase of gap ratio. The attraction between a cylinder and a plane wall, i.e., downward force, occurs when gap ratio lies in certain range. The existence of cylinder changes the pressure gradient on the plane wall and the influence extends to the location where x/D<-3.0 and x/D>5.0.