Free- and Near-Free-Surface Swirling Turbulent Jets

Abstract

he turbulent flowfield created by a round swirling jet issuing from a nozzle, beneath and parallel to a free surface, in both the deep- and shallow-submergence modes has been studied for three swirl numbers (S = 0.265, 0.500, and 0.522) and fixed Froude and Reynolds numbers using a three-component laser Doppler velocimetry system. The results have shown that a swirling jet is unique among all shear flows; stagnation occurs without vortex breakdown at a critical swirl of S = 0.50; vortex breakdown occurs for S ≥ 0.51 and leads to the intensification of turbulence within or near the exit of the nozzle and to the nonmonotonic change of the turbulent kinetic energy with S; turbulence shear stresses exhibit anisotropic behavior, especially in the plane bisecting the jet; and the degree of anisotropy at the free surface depends on the degree of agitation of the free surface (swirl number, Froude number, x/d, and Reynolds number). The need for a robust turbulence model that can deal with the alteration of turbulence by distortion and rotation is emphasized