Computational Studies of Compressibility Effects on Dynamic Stall
Abstract
The dynamic stall characteristics of several airfoils in sinusoidal pitch oscillations as well as in constant rate pitch ramps over a wide range of unsteady flow conditions have been investigated. It is found that the flow before the onset of stall can be considered quasi-steady and predicted using inviscid theory, that the effect of unsteadiness on the onset of dynamic stall depends on the airfoil geometry and whether the flow has become locally supersonic, and that the effect of the freestream Mach number on the onset is rather insensitive to the airfoil geometry. Our analysis on both experimental and numerical results predicts the presence of a separation bubble at the leading edge. It also suggests that the bursting of the bubble, or failure to reattach after the initial separation, is the onset mechanism for most of the dynamic stall cases studied. The effects of transition on bubble bursting (the onset of massive separation of dynamic stall) are studied numerically by choosing the location at which the turbulence model is switched from molecular to turbulent eddy viscosity in the numerical code. It was found that at angles of attack close to the static stall angle, minor movements in the transition point could cause a separation bubble to burst, and that bubble bursting is more susceptible to transition point location in a locally supersonic flow than a subsonic flow. Keywords: Pitch motion/oscillation; Flow separation; Mathematical models; Eddies fluid mechanics; Model tests.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 27, 1990
- Accession Number
- ADA229007
Entities
People
- K.-y. Fung
Organizations
- University of Arizona