Crossflow instability analysis and transition prediction of airfoil boundary layer

Crossflow instability analysis and transition prediction have been done on a 25° swept, 0° attacked airfoil with Mach number 0. 8, unit Reynolds number 6.79×10⁶/m by solving the classic O-S equation (LST), extended O-S equation (EOS) and linear parabolic stable equation (LPSE) together with the e^N method. Results show that the lower branch of the neutral curve in (x, ω) plane does not exist and the shape of the neutral curve in (x, β) plane appears as an antithumb. The crossflow instability plays a key role in the leading edge. As disturbances enter the boundary layer, their amplitude will be enlarged directly. For the same frequence, the disturbances with big wave number β will grow firstly and propogate to a certain place where they begin to decay, then the disturbances with small wave number  β  increased gradually and their increasing factor  N  will exceed that with big wave number finally. Transition occurs in the leading edge of the airfoil and the wave lengh of the inducing wave is about 2mm.