Burst{endash}interface interactions in free surface turbulent flows
- Lawrence Livermore National Laboratory, University of California, Livermore, California 94550 (United States)
Interactions of bursting events (i.e., ejections and inflows) with the free surface in turbulent channel flows have been studied using oxygen bubble visualization and image processing techniques. Experiments indicate that the flow is dominated by the generation of wall ejections, formation of spanwise upsurging vortices, and interaction of such structures with the free surface. The spanwise upsurging vortices are seen to evolve near the wall, reach the free surface, form surface patches, roll back in form of spanwise downswinging vortices, and mix into the bulk flow. There is evidence of horseshoe and hockeystick type vortices in relation to the bursting events. Measurements of surface characteristics show that the ejection{endash}inflow events are associated with deformation of the free surface and a redistribution of near surface vorticity and velocity fields. As upsurging vortices reach the free surface, the surface goes through an elevation, whereas the surface falls when downswinging vortices of the inflowing fluid return toward the wall. These effects are enhanced as the flow Reynolds number is increased. Conditional averaging of the velocity fields shows that while the surface rise is associated with an increase in the streamwise component of turbulence intensities throughout the liquid layer, surface falls are associated with a slight decrease in streamwise intensities near the free surface. Near the wall, all components of intensities are higher for the cases with surface rise than they are for the ones with surface fall. Contour color plots of the velocities and intensities near the interface region depicts these results and show an increase in the number of spanwise vortices rolling in the direction of flow during the ejection{endash}inflow events. Based on these results and observation of video sequences, a conceptual illustration of burst{endash}interface interactions has been provided. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 550384
- Journal Information:
- Physics of Fluids (1994), Journal Name: Physics of Fluids (1994) Journal Issue: 11 Vol. 9; ISSN 1070-6631; ISSN PHFLE6
- Country of Publication:
- United States
- Language:
- English
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