A Study of Wake Vortex in the Scour Region around a Circular Pier

Wake vortex scour is very important when successive piers (one downstream of other) are kept. In case of successive pier arrangement, the wake vortex of the upstream pier may influence the horseshoe vortex of the pier placed downstream. If the piers are arranged eccentrically then the sediment movement may take place towards the side wall of the flume as well as along the downstream. For this reason the study of turbulent flow characteristics of a wake vortex within an equilibrium scour hole is very important. In the present paper the outcome of experimental study on the turbulent wake vortex flow at cylindrical pier measured by an acoustic Doppler velocimeter (ADV) were presented. In this study three different piers were used with diameters 0.10 m, 0.075 m and 0.05 m. Vector plots of the flow field reveal the vorticity and circulation characteristics of the wake vortex flow associated with an upflow at equilibrium scour hole condition. Results show that the non dimensional wake vortex circulation increases at y = 0 and +/- 3 until Rep value reaches around 2.40 . 10(4) but then it decreases with further increase in Rep, as the wake vortices are washed away due to further increase of inertia force. Similar trend was observed when the non-dimensional circulation was presented with respect to different pier diameter as well as at different nondimensional inflow depth. The non-dimensional circulation along the centreline (y = 0) of the flume is lesser than y = +/- 3 which verifies that the wake vortices get weaker when they come closer to the centreline of flow.