Accession Number:

ADA248846

Title:

The Effects of Free Stream Turbulence and Surface Curvature on Boundary Layer Flow and Heat Transfer

Descriptive Note:

Final rept. 1 Jan 1989-31 Dec 1990,

Corporate Author:

STANFORD UNIV CA DEPT OF MECHANICAL ENGINEERING

Report Date:

1992-03-05

Pagination or Media Count:

17.0

Abstract:

The effects of grid-generated, free-stream turbulence up to levels of 7.5 were investigated in a low speed water channel. The distribution of turbulent Prandtl number in the flat-wall region was found to be the same in water as in air, contrary to expectations based on the literature. The effect of Prandtl number on wall trace visualizations of heat transfer was investigated with a liquid crystal surface in a water tunnel. Heat transfer images were dominated by events within the sublayer, fluid mechanics visualizations show effects from far out in the boundary layer. A series of experiments were done in a high turbulence air tunnel 16, uniform across the tunnel to investigate whether or not an abrupt change in flow passage size, with no flow acceleration, would affect heat transfer. A membrane was placed at 13 and 16 of the passage height in a heat transfer tunnel, reducing the largest possible normal scale of the turbulence by that same ratio. There was no significant change in the distribution of heat transfer on the surface under the membrane. A second investigation involved wake-like turbulence interacting with turbulent boundary layers. A wind tunnel experiment is described where spatially-inhomogeneous turbulence, in the absence of mean-velocity variations, is generated by a graded grid which produces intensity levels of 10 at its top and hardly any at its bottom, the part close to a flat wall. Turbulence from the grid diffuses down the intensity gradient and spreads into a turbulent boundary layer on the flat wall.

Subject Categories:

  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE