Buoyancy Effect on Turbulent Round Jet under Regular Waves

Abstract

The mean and turbulence properties of a turbulent buoyant jet discharged at middepth in a direction opposite to the wave propagation direction are experimentally investigated using particle image velocimetry. Three kinds of effluent jets are employed for examining the effects of buoyancy on the interactions of a horizontal round jet in both the jet’s potential core region and the self-similar region with regular waves. By comparing the buoyant jet in a stagnant ambient environment and a wave field, the experiment demonstrates that the widths of the positive and negative jets increase significantly because of the buoyancy effect and the wave dispersion effect—a clear indication of enhanced jet diffusion. As expected, the turbulence intensity and Reynolds stress of the buoyant jet is also significantly influenced when the jet is acted upon by waves. To quantify this influence, the eddy viscosity is calculated on the basis of the measurements. An examination of the buoyant jet’s energy budget shows that when the jet is under the waves, its mean kinetic energy decreases while its turbulent kinetic energy increases, indicating an increase in turbulence production. By examining the near-field property, it is found that the turbulence production, advection, and dissipation terms of the buoyant jet under waves are greater than those of a buoyant jet in a stagnant environment, owing to the greater interaction between the buoyancy effects and the water waves near the free surface.