Periodic vortex shedding phenomenon for various separation distances between two plane turbulent parallel jets

•Unsteady flow characteristics are investigated for various separation distances between two plane parallel jets.•Near flow field demonstrates a von Kármán vortex street when the ratio of separation distance to the jet width lies in the range d/w = 0.6–1.4.•When d/w = 0.5 and 1.5, the near flow field remains steady.•Within the range 0.6 ⩽ d/w ⩽ 1.4, Strouhal number decreases with increasing d/w.

In the present study, two plane parallel jets with various separation distances between the two jets (d) are numerically simulated using two-dimensional unsteady RANS equations. The Reynolds number based on the jet width w is Re = 10,000. The results reveal that when the separation distance between the two jets lies in the range 0.6⩽d/w⩽1.40.6⩽d/w⩽1.4, the flow field demonstrates a periodic vortex shedding phenomenon close to the nozzle plate similar to what would be expected in the near wake region for flow over a two-dimensional bluff body. On the contrary, for d/wd/w = 0.5 and 1.5, the near flow field region remains to be steady with two counter rotating stable vortices in the recirculation zone. Within the range 0.6⩽d/w⩽1.40.6⩽d/w⩽1.4, the time series of streamwise and transverse velocity signals display a pure sinusoidal oscillation. In this range, for a given d/wd/w, the fast Fourier transform of both the velocity signals exhibits a single dominant frequency peak at a same value of Strouhal number (non-dimensional vortex shedding frequency) that gradually decreases with the progressive increase in the separation distance between the two jets.