ON THE CONTROL OF CIRCULAR-CYLINDER FLOW BY END-PLATES

The present work involves an experimental study of the effect of end p late boundaries on the flow around a circular cylinder for Reynolds nu mbers 4 x 10(3)-4.8 x 10(4) and cylinder aspect ratios 0.25<L/d<27.6. The deviation from uniformly distributed flow along the body span is m easured and discussed. End plate design is found to have a strong infl uence on the spanwise variation of the base pressure. A sufficiently l ong trailing edge distance is of vital importance in obtaining as unif orm a pressure distribution along the span as possible, but the leadin g edge distance is also found to influence the flow. Within the measur ed Reynolds number range it is possible to define an optimized end pla te design that, as far as possible, reduces spanwise flow nonuniformit ies. The end plate performance is markedly better at Re = 4 x 10(4) th an at 1 x 10(4). The influence of the end plate horse shoe vortex laye r is found to be weak. Details of its formation are analysed and discu ssed. Varying the cylinder aspect ratio showed a strong Reynolds numbe r dependence and extreme flow patterns were found at an aspect ratio a round 1. Keeping the aspect ratio at about 1, in combination with the use of a short leading edge distance, was found to inhibit the onset o f vortex shedding, resulting in a steady wake for Re<1 x 10(4). At Re = 4 x 10(4), in contrast, a peak in base suction indicating the strong est vortex shedding was observed with L/d=1.