Passive control of circular cylinder wake in shallow flow

► Both plate length and height ratio are important parameters for the suppression of the vortex shedding in shallow water. ► Flow characteristics show that Karman vortex shedding is attenuated pronouncedly for the cases of L/D⩾1 and hp/hw⩾0.75. ► The plate height ratio hp/hw=1 is the most effective case on the attenuation of vortex shedding. ► 〈v′v′〉/U2 is more effective on the attenuation of turbulent kinetic energy than 〈u′u′〉/U2. The control of vortex shedding of a circular cylinder in shallow water using a splitter plate located in the downstream of the circular cylinder was studied by employing particle image velocimetry (PIV) technique. Experiments were carried out in a water channel having a test section of 8000mm×1000mm×750mm dimensions at a Reynolds number of 6250. The length of the splitter plate (L) was varied within the range of 0.5⩽L/D⩽2 with an increment of 0.5. The plate was submerged into water at different height ratios (hp/hw) such as 0.25, 0.5, 0.75 and 1.0. Mean velocity vector field, corresponding vorticity contours, streamline topologies and turbulent quantities were calculated using 300 instantaneous velocity vector field measured by PIV. As the ratio of hp/hw increases, the effect of the splitter plate on the suppression of the vortex shedding increases. Flow characteristics and examination of spectra indicate that Karman vortex shedding is attenuated pronouncedly for the cases of L/D⩾1 and hp/hw⩾0.75. The transverse Reynolds normal stress is more effective on the attenuation of turbulent kinetic energy than the streamwise Reynolds normal stress. The value of peak transverse Reynolds normal stress is reduced to 90% of that of the bare cylinder at most.