Free- and near-free-surface swirling turbulent jets

The 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 greater than or equal to 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, rid, and Reynolds number). The need for a robust turbulence model that can deal with the alteration of turbulence by distortion and rotation is emphasized.