Flow structures in the wake of a square cylinder inclined with angles of  = 0, 15, 30 and 45 undergoing forced oscillation are investigated experimentally using particle image velocimetry (PIV) at Keulegan-Carpenter (KC) numbers in the range of 5-30 to examine the performance of the Independent Principle (IP). For KC < 6, there is no vortex shedding from the cylinder for all angles and as a result, the IP is valid. For KC 820, IP does not work satisfactorily because at large inclination

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... gles, the shear layers are stretched and reattach to the upper and lower sides of the cylinder body for most of the time within one oscillating cycle. When KC is increased further to 25, the phenomenon of shear layer attachment when the cylinder is at the neutral position, as well as the significant shedding at the end of each half cycle, indicate a similar flow field for both vertical and inclined cylinders. The present investigation indicates that the IP is valid when KC  6 and KC  20 as it is analogous to a steady current.