Submerged turbulent twin jets interacting with a free surface and a solid wall

Abstract

The mean flow properties and turbulence characteristics of submerged twin jets interacting with a free surface or a solid wall are investigated using particle image velocimetry. The experiments were performed with two parallel round nozzles of transverse separation ratio, G/d = 2, where d is the nozzle diameter, and jet exit Reynolds number, Re = 5000. The effects of offset ratio and boundary condition were investigated by positioning one of the jets closer to a free surface or a solid wall at offset heights of 1d, 2d and 4d, while the other jet is sufficiently far from the opposite boundary. The results indicate that the decay rate of the jet closer to the boundary decreased with offset ratio but was independent of boundary condition. The effects of the boundary condition on the mean velocities and Reynolds stresses were confined to the immediate vicinity of the boundary. In this region, the transverse turbulence intensity and Reynolds shear stress were reduced, but the reduction was more dramatic near the wall than the free surface. Unlike the solid wall, the relaxation of the no-slip condition at the free surface and the reduction in transverse turbulence intensity gave rise to high streamwise turbulence intensity at the free surface. As offset ratio decreased, the surface mean velocities and turbulence intensities beyond the attachment point increased considerably. Two-point auto-correlations of the velocity fluctuations demonstrated that the spatial coherence of the turbulence structures increases with increasing offset ratio and the extents of the transverse auto-correlation, Rvv are reduced in the far field near the solid wall compared to the free surface cases.