THE SINGLE STRIP-INDUCED CHANGE OF 2P-MODE VORTEX SHEDDING IN THE WAKE OF A TRANSVERSELY OSCILLATING CYLINDER

The control of vortex shedding from a forced oscillating cylinder is the basis of control of vortex-induced cylinder vibration, and of significance in civil and ocean engineering. A lock-on mode of vortex shedding called 2P mode exists in the wake of an oscillating cylinder, i.e., in a period of oscillation, a pair of vortices shed from each side. A strip element of width b/D=0.32 is used and set in the wake to influence the 2P mode vortex shedding at oscillating amplitude A/D=1.25, frequency f_e D/V_∞=0.22, and Reynolds number Re=V_∞ D/ν=1 200. Using the method of 2D large eddy simulation with experimental confirmation, we find that with the change of strip position in the area 0.8≤X/D≤3.2, 0.4≤Y/≤3.2, vortex shedding is changed between 2P, 2S, P+S and other 6 new modes. The detailed generation process of every mode of vortex shedding is described in the paper. The zones of the modes and the contours of vortex strength are figured out on the plane of strip position. It is shown that vortex strength can be reduced by 50% or more and the wake is narrowed if the strip is set at places in a considerably large region. The transverse shear flow induced by large amplitude cylinder oscillation plays a key role in the generation of vortex shedding. The influence of the strip on the transverse shear flow is discussed and the mechanism of the strip function to the formation of every mode of vortex shedding is analyzed.