Abstract
This paper describes the velocity fluctuation of flow around a rectangular cylinder, when the free stream velocity changes in time. This change is made by a flow control device placed at the exit of the wind tunnel. In this report we focused on the case where the free stream was decelerated, in Re number, from 4000 to 0 and then was accelerated up to 4000 again. Experimental results obtained by means of a hot-wire anemometer were processed by through wavelet transform in order to examine the relation between the free stream velocity and the fluctuation frequency spectrum which indicates the scale of vortices shed from the cylinder. Flow visualization was also carried out by the smoke wire method. Results show dearly the developing and collapsing process of vortices in the wake according with the velocity change. Especially, with respect to the vortex developing with the free stream acceleration, noteworthy differences were observed in beginning of vortex shedding according to whether the acceleration was following to the deceleration or not.
