Instability of non-parallel boundary layer

The phenomenon of transition from laminar to turbulent flow becomes of primary importance when the design of airplanes or rockets is considered. Transition prediction methods so far have been based on semi-empirical method using linear parallel stability theory (local theory), or on direct numerical methods. Driven by the need to obtain more accurate calculations than those yielded by the local theory and less expensive than using the direct methods, Bertolotti [1] introduced the parabolized stability theory. In parabolized stability theory the local disturbance growth is influenced by local flow conditions and upstream spatial amplification whereas in the local stability theory local growth is influenced only by local flow conditions. In the parabolized stability theory the effect of boundary laver growth and other history effects asscoiated with initial conditions can be properly accounted for. In the present paper a parbolized stability theory is described and used to study the transition region in hypersonic flow around the sharp and blunt cone of zero angle of attack.