Accession Number : ADA311791

Title :   Manipulation of Airfoil Response in an Unsteady Stream.

Descriptive Note : Final technical rept. 1 Mar 92-28 Feb 95,

Corporate Author : CALIFORNIA UNIV LOS ANGELES DEPT OF MECHANICAL AEROSPACE AND NUCLEAR ENGINEER ING

Personal Author(s) : Ho, Chih-Ming

PDF Url : ADA311791

Report Date : 31 JAN 1996

Pagination or Media Count : 61

Abstract : Experiments were conducted to investigate the mechanism responsible for vortex breakdown over delta - wing. By varying the free stream velocity, unsteady vortex breakdown occurs over the wing due to the alteration of the balance between leading-edge vorticity production and convection. This allows the study of vortex breakdown in both the spatial and temporal domain. It was found that parameters such as swirl angle and circulation do not correlate well with breakdown when the flow is unsteady. However, vortex breakdown seemed to follow the positive feedback mechanism proposed by Brown and Lopez. When breakdown occurs, there is a redistribution of vorticity in the vortex subcore, where the vorticity vector changes from an essentially axial direction to a generally tangential direction. Further, the helix angle for the velocity exceeds that of the vorticity globally in the vortex subcore only in the instant just before breakdown. Finally, it was found that through breakdown, global quantities such as circulation and flow rate varies in phase as the upstream vorticity and velocity changes with time. This implies that the breakdown process is essentially an inviscid mechanism.

Descriptors :   *AERODYNAMIC CHARACTERISTICS, *UNSTEADY FLOW, VELOCITY, PRODUCTION, QUANTITY, CONVECTION, VORTICES, AIRFOILS, FLOW RATE, RESPONSE, FEEDBACK, TANGENTS, WINGS, INVISCID FLOW, FREE STREAM, DELTA WINGS.

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE