Strouhal number of flat and flapped plates at moderate Reynolds number and different angles of attack: experimental data

Abstract

This paper is devoted to considering the Strouhal number (St) of various geometries of a plate at different angles of attack ( $$0^{\circ }$$ – $$90^{\circ }$$ ), while the Reynolds number ( $${\textit{Re}}$$ ) changes in a moderate range (between $$2.8\times 10^{\mathrm {4}}$$ and $$1.4\times 10^{\mathrm {5}})$$ . The considered geometries consist of a flat plate and a flapped plate. Two of its flaps make a cross section like a flattened S and are investigated with flap angles of $$27^{\circ }$$ and $$55^{\circ }$$ . The frequency of vortex shedding is measured using two strain gauges mounted in X shape on the central axis of the plates. The experimental results have been corrected for blockage effect. Based on the results, St of the flat plate increases sharply from zero angles of attack up to $$50^{\circ }$$ , and then reaches an almost constant value at higher angles. The experiments demonstrate that the flapped plate suppresses the vortex shedding at a certain range of angles of attack compared with the flat plate. Consequently, St of the flapped plate becomes smaller than in the case of the flat plate in this range. The effect of the flow regime in a channel on St of the flat plate is probed using different hydraulic Froude numbers relevant to subcritical, critical and supercritical regimes.