Interaction of a turbulent round jet with the free surface.

An experimental study of the interaction of an underwater turbulent round jet with the free surface was conducted. Flow visualization, surface curvature measurements and hot film velocity measurement were used to study this flow. It is shown that surface waves are generated by the large scale vortical structures in the jet flow as they approach the free surface. These waves propagate at angle with respect to the flow direction. The propagation angle increases as the strength of the interaction is increased by increasing the momentum flux of the jet or reducing the distance of the jet to the free surface or both. Propagation of these waves in the flow direction is suppressed by the surface current produced by the jet. Far downstream the surface motions are caused by the large scale vortical structures interacting directing with the surface. The fundamental scaling parameters of the free-surface jet determined. The velocity scale is the velocity obtained from the combination of jet momentum, density and depth of the jet and the scale is the distance of the jet to the free surface. It is shown that the centerline velocity decay when scaled with these parameters collapses to a universal curve for different depths of the jet. The asymptotic decay in the far field is reduced by a factor of 2$\\sp{1/2}$ compared to the free jet due to the confinement by the free surface. The growth rate of the free-surface jet is found in good agreement with the free jet. However the eccentricity of the jet cross section caused by the displacement of the jet centerline persists for large distances downstream, beyond 40 times the initial depth of the jet centerline. Measurements are also reported on the flow field of a jet moving parallel to a solid surface. These results are compared with the results for the free surface jet. It is found that the solid wall jet flow is fundamentally different from the free-surface jet flow. The growth rate of the wall jet in the direction parallel to the surface is approximately 3.9 times the growth rate of the free-surface jet. The growth rate of the wall jet in the direction perpendicular to the surface is half the free-surface jet growth rate. This is the result of the different dynamics of vorticity on the free surface compared to a solid wall. The skin friction at the solid wall and increased growth rate combined to give a different maximum velocity decay rate compared to the free-surface jet.PhDAerospace engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/162340/1/9001677.pd