Flow Characteristics around a Circular Cylinder Placed Horizontally above a Plane Boundary

Flow characteristics around a circular cylinder positioned near a plane boundary (on which laminar boundary layer flow develops in the absence of circular cylinder), are investigated for Reynolds numbers R ranging from 7.8× 102 to 1.15× 104 . Particle image velocimetry and fiber laser Doppler velocimetry were used to measure the velocity fields and velocity time histories, respectively. Flow structures are particularly revealed using flow visualization technique at R=7.8× 102 for gap ratios G∕D (where G is the net gap between the surface of circular cylinder and the plane boundary), varying from 0 to 4. Based on the experimental results, the variation of Strouhal number of shedding vortex (or eddy) with G∕D , the mechanism of vortex shedding suppression, and the streamwise velocity profiles of the upper shear layers and gap flows for small G∕D are all discussed. Although the regular, alternate vortex shedding is suppressed for G∕D<0.5 , the periodicity could be detected due to the vortex (or eddy) sheddin...