Accession Number : ADA187261

Title :   An Analysis of the Motion and Effects of Hairpin Vortices.

Descriptive Note : Interim rept. Jul 85-Jul 87,

Corporate Author : LEHIGH UNIV BETHLEHEM PA DEPT OF MECHANICAL ENGINEERING AND MECHANICS

Personal Author(s) : Hon, Thon-Lon ; Walker, James D

PDF Url : ADA187261

Report Date : Jun 1987

Pagination or Media Count : 223

Abstract : Recent studies suggest that the hairpin vortex plays an important, possibly dominant, role in the dynamics of turbulent flows near walls. This study addresses the following topics of the motion of hairpin vortices near solid walls on a theoretical basis: the nature of the evolution of hairpin vortices in a shear flow; the type of flow induced near a wall by a convected hairpin vortex; the character of the viscous response near a wall to the hairpin vortex motion; and the nature of the interaction of 2 hairpin vortices. A numerical procedure is developed to allow accurate evaluation of the trajectory of a 3-dimensional vortex for vortices having small cores. The integration method is based on a numerical approximation to the Biot-Savart integral; most existing vortex calculation methods have severe stability problems for vortices with small cores. These problems are overcome with the present method and technique is applied to compute the evolution of convected vortex loops and hairpin vortices, both in uniform flow and in shear flow above a wall. For hairpin vortices evolving in a shear flow, a regenerative process is observed wherein secondary hairpin vortices form outboard of the original hairpin vortex in a manner consistent with experimental observations. Calculations for 2 hairpin vortices, initially close to one another in a shear flow, show that the vortices interact to reinforce one another. Simulations carried out to compute the evolution of hydrogen bubble lines as a hairpin vortex passes show that such vortices can give rise to wall layer streaks.

Descriptors :   *VORTICES, *TURBULENT BOUNDARY LAYER, DYNAMICS, APPROXIMATION(MATHEMATICS), SHEAR PROPERTIES, TURBULENT FLOW, WALLS, VISCOSITY, INTEGRATION, NUMERICAL METHODS AND PROCEDURES, STABILITY, INVISCID FLOW, VISCOUS FLOW, INTERACTIONS

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE