On the structure of a two-dimensional wake behind a pair of flat plates

Unsteady and asymmetric vortex shedding was investigated experimentally in the wake of two flat plates placed side by side normal to the flow. The experiment was conducted in water at Re= 1500 based on an individual plate width. The spacing between the plates was varied from one plate width to two plate widths. For a small spacing between the plates, the deflection of the jet passing through the gap resulted in a larger wake with mostly symmetric vortex shedding on one side and a smaller wake with asymmetric shedding on the other. The intermediate wake for the small plate spacing resembled that of a single bluff body, whereas a more intermittent structure was observed at the wider spacing. The velocity time traces were obtained by laser Doppler velocimetry (LDV) at several locations in the wake. The Fourier spectra of the velocity data at certain positions indicated the presence of more than one dominating frequency. Wavelet analysis mapped the intermittent near-periodic structures, and quantified their mean energy spectrum in relation to the ensemble mean. These results are interpreted by comparison with flow visualization data.