Accession Number : ADA311428

Title :   Three-Dimensional Aspects of Nominally 2-D and 3-D Bluff Body Wakes.

Descriptive Note : Final rept. Jan 90-20 Jun 94,

Corporate Author : CORNELL UNIV ITHACA NY

Personal Author(s) : Williamson, C. H.

PDF Url : ADA311428

Report Date : 29 DEC 1995

Pagination or Media Count : 4

Abstract : Over the last decade, there has been much work carried out to understand three-dimensional effects at low Reynolds numbers (Re) in the wake of bluff bodies, yielding the reaction that end effects can influence the vortex shedding across large spanwise lengths. Wake patterns such as parallel shedding, oblique shedding, cellular shedding, transient patterns, such as 'phase shocks' and 'phase expansions', as well as the existence of large-scale 'vortex dislocations', have been investigated, aspects of this research being spearheaded by me studies at Cornell under the above Contract. In particular, we have discovered a new mechanism for oblique wave resonance in the far wake. We have found a means to control the near wake by using suction at the spanwise ends of a body, which has enabled much more precise phenomena to be investigated including the critical conditions for turbulence inception, and a careful study of 3-D wake transition. We have combined our research at Cornell with studies by Dr. Peter Monkewitz at Ecole Polytechnique, Lausanne, who has effectively laid much of the foundation of the description of these near wake patterns in terms of a Guinzburg-Landau equation. For example, the now transient phenomenon known as a 'phase expansion' has been found to be directly analogous to a Prandtl-Meyer expansion found in gas dynamics. Clearly, the work under the support of the ONR has led to a surprisingly rich new understanding of three-dimensional effects in nominally two-dimensional wake flows.

Descriptors :   *WAKE, SHOCK WAVES, TURBULENCE, VORTICES, COMPUTATIONAL FLUID DYNAMICS, VORTEX SHEDDING, GAS DYNAMICS, FLOW FIELDS, TWO DIMENSIONAL FLOW, UNSTEADY FLOW, BOUNDARY LAYER TRANSITION, REYNOLDS NUMBER, BOUNDARY LAYER CONTROL, THREE DIMENSIONAL FLOW, PRANDTL NUMBER.

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE