THE EFFECTS OF 3-DIMENSIONAL IMPOSED DISTURBANCES ON BLUFF-BODY NEAR WAKE FLOWS

Wind tunnel and water flume experiments have been carried out on a half ellipse model with a blunt trailing edge, the aim being to study the three-dimensional nature of vortex shedding. The trailing edge of the model can be either straight or mildly wavy. Introducing waviness reduces base drag, with the reduction higher at the peaks of the waves, corresponding to where the chord is a maximum, than at valleys. Two vortex shedding frequencies are observed and there are two main modes of shedding, one where it is symmetric about a peak and the other where it is antisymmetric. Vortex splitting is a common feature observed in the flow and this occurs in order to accommodate changes in shedding frequency along the span. Behind a straight trailing edge vortex splitting occurs at random positions whereas superimposed waviness tends to fix where the splitting takes place.