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.