Turbulence Near a Free Surface in a Plane Jet
Abstract
Laboratory measurements of the turbulent flow in a plan e jet issuing at the free surface are reported and analyzed. Single point hot-film data were obtained for mean velocities and turbulent fluctuations of velocity and shear stress in the developing jet to (X sub 1)/(b sub 0) = 240 with an emphasis on the near surface turbulent behavior. Synoptic behavior of the jet resembled that of a 2D wall jet rather than one half of a planar free jet with the free surface represented by the symmetry plane. The effects of jet confinement are to retard the ability of the jet to entrain fluid, to decrease the growth rate of the length scale and to increase the decay rate of the velocity scale. Mean velocity profile similarity is still observed when the data is non-dimensionalized with the reduced scales. Jet momentum will appear to have been lost due to momentum exchange with the return flow. An approximate analysis provides a means to estimate the momentum loss due to limited depth and is shown to correlate well with scale development in several jet configurations for these and prior experiments. One-dimensional turbulence spectra revealed 'blocking' of certain vertical scales as the free surface is approached with a concommitant redistribution of turbulent kinetic energy from the vertical fluctuations to the lateral components. This is in qualitative agreement with recent analyses and experiments for isotropic turbulence near moving walls and free surfaces but differs by exhibiting a wider range of surface-influenced turbulent length scales and a thinner influenced layer below the free surface.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 14, 1989
- Accession Number
- ADA206269
Entities
People
- M. A. Plesnia
- S. E. Ramberg
- T. F. Swean Jr.
Organizations
- United States Naval Research Laboratory