Effect of bottom wall proximity on the unsteady flow structures of a combined turbulent wall jet and offset jet flow

The present paper deals with a turbulent dual jet consisting of a wall jet and an offset jet. The flow field has been numerically simulated using two-dimensional unsteady RANS equations. The Reynolds number based on the separation distance between the two jets (s) is Re = 10, 000. The width of the offset jet nozzle equals the separation distance between the two jets. To examine the influence of the bottom wall, the width of the wall jet nozzle (h) has been varied in a range 0.2 <= h/s <= 2. According to the computational results, for h/s = 0.2, the flow field remains to be always steady with two counter-rotating stable vortices in between the two jets. On the contrary, within the range of 0.3 <= h/s <= 1, the near flow field demonstrates a periodic vortex shedding phenomenon similar to what would be observed in the near wake region for flow over a two-dimensional bluff body. Within this flow regime, the Strouhal number based on the vortex shedding frequency gradually decreases with the progressive increase in h/s. However, for h/s > 1, although the periodic vortex shedding phenomenon is still evident in the flow field, the Strouhal number becomes insensitive to the bottom wall similar to the flow behaviour for a flow over an unconfined cylinder. (C) 2015 Elsevier Masson SAS. All rights reserved.