ON THE INSTABILITY OF FLOW IN A STREAMWISE CORNER

The linear stability of an incompressible laminar flow in the blending boundary layer between the boundary layer in a 90-degrees streamwise corner and a Blasius boundary layer well away from the comer is examin ed using a locally parallel flow approximation. It is shown that the m agnitude of the cross flow in the boundary layer is too small to be a significant factor in the observed early transition in the blending la yer. However, the influence of the outer boundary conditions associate d with oblique modes of disturbances which are anti-symmetric about th e bisector plane are shown to have a profound effect on the stability of the flow. As a result, the square root of the critical streamwise R eynolds number, R(cr), associated with a spanwise location is signific antly reduced as the corner is approached, being R(cr) = 54 approximat ely for spanwise distance of z = 6x*R-1 from the corner compared with R(cr) = 322 approximately for z = 20x*R-1, where x* measures downstr eam distance from the leading edges and R2 is the streamwise Reynolds number. At R = 600, the growth rate of the most amplified mode of dist urbance at the former location is over six times greater than that at the latter; the corresponding wave angle at the two locations is respe ctively 44-degrees and 5-degrees, approximately.