Accession Number:

ADA303767

Title:

Quasi-Periodicity In Vortex Flows.

Descriptive Note:

Final technical rept. Nov 92-Sep 95,

Corporate Author:

GEORGIA INST OF TECH ATLANTA SCHOOL OF AEROSPACE ENGINEERING

Report Date:

1995-10-13

Pagination or Media Count:

62.0

Abstract:

Part 1 summarizes the search for the origin and nature of nearly-periodic velocity fluctuations observed over fighters at incidence angles between 15 and 40 deg. The Strouhal number and spectral shape remain constant over a wide range of Reynolds number, but vary with incidence and sweep. A 132-scale F-15 and a 59.3-deg. cropped delta flat plate are used for detailed studies, but the phenomenon is general to leading-edge vortex flows. Empirical correlations are developed for various aircraft configurations and wing planforms. Cross-spectral analysis traced the fluctuations upstream along a helical path to the surface. Streaklines and laser velocimetry discovered spanwise counter-rotating structures in the surface shear region under the vortex, amplifying downstream. Remaining hypotheses are based on centrifugal instability and unsteady vortex-surface interaction. Surface mini-fences modified and attenuated the spectra by as much as 50, reinforcing the finding of amplification from the surface layer. Part 2 details improvements to the High Angle of Attack Stability and Control code predicting swept-wing configuration aerodynamics. Effects of camber, edge bevels, and of multiple vortices on vortex loads and breakdown are accurately predicted, as well as the turbulent vortex core size. AN

Subject Categories:

  • Aerodynamics
  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE