AIAA, Aerospace Sciences Meeting & Exhibit, 35th, Reno, NV, Jan. 6-9, 1997 We review experimental and computational studies of free-surface turbulent jets and report on a recently completed experimental study of the interaction of a coflowing jet with the free surface. The mean flow scaling and the turbulent structure were measured. The vertical structure at the surface is determined using particle image velocimetry. The presence and evolution of the surface current, as well as enstrophy

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... ion at the surface, are documented. The results show a complex highly 3D interaction. ABSTRACT We review experimental and computational studies of freesurface turbulent jets and report on a recently completed experimental study of the interaction of a cotlowing jet with the free surface. The mean flow scaling and the turbulent structure were measured. The vortical structure at the surface was determined using particle image velocimetry (P1V). The presence and evolution of the surface current is documented as well as enstrophy production at the surface. The results show a complex highly three dimensional interaction. Enstrophy production at the surface is localized at the location where vortex rcconnection processes occur. Madnia and Bernai" report measurements of the mean flow and surface signature of a free-surface jet. They found a reduction of the decay rate of the maximum velocity due to the presence of the surface. At sufficiently high Froude number Associate Professor, Senior Member AIAA. ( Fr = Ue^/gh ), the interaction of large scale structures in the jet with the surface produces surface waves that propagate in the lateral direction. The amplitude of the surface deformation was characterized by surface curvature measurements. They also noted the onset of swirls on the free surface associated with vorticity normal to the free surface. Anthony and Willmarth 1 report three-component LDV measurements of the mean velocity and turbulent Reynolds slresses in a free-surface jet. They note anisotropy of the normal components of the Reynolds stress near the surface. This effect, which was first observed by Swean et al. 4 is consistent with a dominance of surface normal vorticity at the free surface. Anthony and Willmarth also identify the presence of a thin outward flow region near the surface that they called "the surface current". The surface current is attributed to surface parallel vorticity interacting with its image and propagating away from the centerline. Walker, Chcn, and Willmarth* have extended the work of Anthony and Willmarth. They also used a three component LDV and measure turbulence statistics at two downstream locations. By using large ensemble sizes they were able to accurately calculate the mean velocity vector and Reynolds stress tensor for selected measurement locations. Cases with two Froude numbers and two Reynolds numbers were considered where these parameters varied by an order of magnitude. Their work confirms the presence of a surface current and attributes its formation to streamwise. surface-tangent vorticity interacting with its image above the surface and propagating outward. This outward propagation of vorticity increases the tangential velocity fluctuations near the surface at the expense of the surface normal fluctuations causing anisotropy of the Reynolds stress tensor. At high Froude number, surface disturbances increase and radiate energy away from the flow in the form of waves. This has the effect of reducing the vortex interaction process and damping the surface current. Walker et al. 5 show a reduction in turbulent kinetic energy of up to 20% for the high Froude number case. The effect of increased Reynolds number was shown to slow the growth and decay of the jet with downstream distance. Mangiavacchi' performed direct numerical simulations of a temporally growing round turbulent free-surface jet. Statistics and turbulence structure were found to be in good agreement with the previous experimental results. The numerical results show the anisotropy of the turbulent fluctuations near the free surface and the generation of the surface current. Both surface normal and surface tangent vortex structures were identified. For