PRIMARY AND SECONDARY INSTABILITIES OF THE ASYMPTOTIC SUCTION BOUNDARY-LAYER ON A CURVED PLATE

The temporal growth of Gortler vortices and the associated secondary i nstability mechanisms are investigated numerically in the case of an a symptotic suction boundary layer on a curved plate. Highly inflectiona l velocity profiles are generated in both the spanwise and vertical di rections. The inflectional velocity profile develops earlier in the sp anwise direction. There exist two distinct modes of instability that e ventually lead to the breakdown of Gortler vortices: the sinuous mode and the varicose mode. The temporal secondary instability analysis of the three-dimensional inflectional velocity profile reveals that the s inuous mode becomes unstable earlier than the varicose mode. The sinuo us mode is shown to be primarily related to shear in the spanwise dire ction, partial derivative U/partial derivative z, and the varicose mod e to shear in the vertical direction, a partial derivative U/partial d erivative y.