Effect of a splitter plate on the near-wake development of a semi-circular cylinder

Abstract

Addition of a splitter plate along the wake centerline downstream from bluff bodies is an efficient passive means of controlling fully developed vortex shedding. The objective of this work is to observe, by means of solid tracer visualizations, the influence of such plate control on the early near-wake establishment stages of a semi-circular cylinder (SCC) geometry ( 0⩽t ∗ ⩽10 ). The splitter plate has a fixed length, equal to one obstacle diameter D , and its position from the SCC was examined using three different gaps g : g =0.0 D , 0.5 D and 1.0 D . Experiments were performed for two Reynolds numbers, Re=200 and Re=400. Splitter plate presence generates secondary vortices in the recirculating zone and modifies near-wake time evolution with regard to that of the single SCC. Indeed, for the single SCC, the recirculating zone, composed of two counter-rotating vortices, develops with time and concurrently, vortex shedding takes place. With the splitter plate, the main vortices, initially in part or fully separated by the plate, are pushed with time to the splitter plate trailing edge. Their interaction induces vortex shedding which begins according to splitter plate position at the same dimensionless time, and sometimes, even sooner than in the case of a single SCC. However, particular configurations delay Bénard-Von Kármán alternate vortex shedding onset. In the observation time range, these splitter plate configurations are g =0.5 D for Re=200 and g =1.0 D for Re=400. In order to improve these results, an open loop active control system has been put into place. The objective is to give a translatory motion to the splitter plate in order to limit, in time, main vortex interaction of the recirculating zone and thus, slow down and even inhibit the vortex shedding process.