Vortex Instabilities in 3D Boundary Layers: The Relationship between Gortler and Crossflow Vortices
Abstract
The inviscid and viscous stability problems are addressed for a boundary layer which can support both Goertler and Crossflow vortices. The change in structure of Goertler vortices is found when the parameter representing the degree of three-dimensionality of the basic boundary layer flow under consideration is increased. It is shown that Crossflow vortices emerge naturally as this parameter is increased and ultimately become the only possible vortex instability of the flow. It is shown conclusively that at sufficiently large values of the crossflow there are no unstable Goertler vortices present in a boundary layer which, in the zero crossflow case, is centrifugally unstable. The results suggest that in many practical applications Goertler vortices cannot be a cause of transition because they are destroyed by applications Goertler vortices cannot be a cause of transition because they are destroyed by the 3-D nature of the basic state. In swept wing flows the Goertler mechanism is probably not present for typical angles of sweep of about 20 degrees. Some discussion of the receptivity problem for vortex instabilities in weakly 3-D boundary layers is given; it is shown that inviscid modes have a coupling coefficient marginally smaller than those of the the fastest growing viscous modes. However the fact that the growth rates of the inviscid modes are the largest in most situations means that they are probably the most likely source of transition. Keywords: vortex, instability, crossflow.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1990
- Accession Number
- ADA228696
Entities
People
- Andrew P. Bassom
- Philip Hall