Accession Number:

ADA272011

Title:

Low Reynolds-Number Turbulent Boundary Layers

Descriptive Note:

Final rept. 14 Apr 89-30 Mar 93,

Corporate Author:

CLEMSON UNIV SC DEPT OF MECHANICAL ENGINEERING

Personal Author(s):

Report Date:

1993-06-30

Pagination or Media Count:

58.0

Abstract:

An experimental investigation was performed to determine the Reynolds analogy factor and turbulent Prandtl number in the transitional and low- Reynolds-number turbulent boundary layer. A miniature three-wire probe was specially designed to measure the mean velocity and temperature profiles and the Reynolds stresses and heat fluxes. Tests were conducted over a heated flat wall with zero pressure gradient and three levels of streamwise acceleration K 0. 07, 0.16, and 0.25 x 10-6. Mean temperature profiles lagged in development compared to the mean velocity profiles and the values of the Reynolds analogy factor, 25tCf, in the late-transition and early-turbulent regions were lower than the values known to apply to the high-Reynolds-number turbulent flow. The profiles of Reynolds cross-stream heat flux showed negative values in the near wall region. The region of negative vt narrowed as the flow proceeded downstream. These negative values of vt in a flow with a negative mean temperature gradient result in negative eddy thermal diffusivity and negative Prt. It is speculated that the negative values might be caused by the size of the sensor and the three-dimensional behavior of transition. A conditional sampling technique was utilized to separate the flow into turbulent and non- turbulent portions. Detailed flow and thermal structures were investigated.

Subject Categories:

  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE