Accession Number:

ADA179603

Title:

An Experimental Study of Hairpin-Type Vortices as a Potential Flow Structure of Turbulent Boundary Layers.

Descriptive Note:

Interim rept.,

Corporate Author:

LEHIGH UNIV BETHLEHEM PA DEPT OF MECHANICAL ENGINEERING AND MECHANICS

Personal Author(s):

Report Date:

1984-10-01

Pagination or Media Count:

391.0

Abstract:

A water channel study examined the suggestion that hairpin vortices exist in the near-wall region of turbulent boundary layers and play a key role in the turbulence production process. The hairpin vortices were generated by the interaction of either 1 a hemisphere proturberance or 2 a low-speed fluid region created by fluid injection techniques with a subcritical, laminar boundary layer. Shedding characteristics of the hemispheres and the roll-up characteristics of the low-speed regions were determined using hot-films anemometry. Three dimensionality of the flow in the region of hairpin generation results in amplification of disturbances of shorter wavelengths than predicted from two dimensional stability theory. Flow visualization techniques documented the flow patterns created by the presence of the hairpin vortices. Comparision of these patterns with comparable visualizations of fully turbulent boundary layers is quite striking, indicating essential identity between hairpin vortices and many of the predominant flow patterns observed in the near-wall region of a turbulent boundary layer e.g. streaks, bursts, pockets, ejections, etc.. Velocity measurements made using hot-film anemometry indicate the presence of strong inflectional profiles just down-stream of the hairpin vortex generation region which evolve into fuller profiles with downstream distance, eventually developing a remarkable similarity to a turbulent boundary layer velocity profile. A comprehensive model of the flow process in the near-wall of a turbulent boundary layer is presented.

Subject Categories:

  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE