Numerical investigation of steady and periodically unsteady flow for various separation distances between a wall jet and an offset jet

The effects of separation distance between two jets in the near field region of turbulent dual jet flow consisting of a wall jet flow and an offset jet flow have been investigated using two-dimensional unsteady RANS equations. The unsteady fluid mechanics of two interacting jets have been illustrated by means of time series analysis of the instantaneous flow field. For a comprehensive understanding of the fluid mechanics, computation has been carried out at a large number of values of the ratio of separation distance (d) and jet width (w) for finely resolving the relevant range of d/w. Results show that when d/w lies in the range 0.7≤d/w≤2.1, the near field of the flow domain is characterized by a periodic large scale von Kármán-like vortex shedding phenomenon similar to what would be expected in the wake of a bluff body. On the contrary, for d/w≤0.6 and d/w≥2.2, no periodic vortex shedding is detected; rather, a pair of steady counter rotating stable vortices are formed in between the two jets close to the nozzle plate. Fast Fourier transform of the velocity signals provides vortex shedding frequency corresponding to the Strouhal number that decreases with the increase in separation distance between the two jets.