As the most important disturbance source

the wakes dominate the instability and transition process of boundary layer in low-pressure turbines. A detailed experimental study on the velocity fluctuation in a laminar separated shear layer on the flat plate of low-pressure turbine pressure distribution with the hot-wire probe at Reynolds number of 130000 were presented. The disturbance development under stable and instable incoming conditions was compared to analyze the influence of the wakes on the destabilization mechanism. Results show that the disturbance grows linearly in the former part of the separation bubble

and nonlinear interaction appears when the disturbance saturates

leading to vortex shedding at the maxima height of the bubble. Inviscid K-H(Kelvin-Helmholtz) mechanism dominates the instability process in the separation bubble. The occurrence of convective linear instability mechanisms was also revealed when amplifying the velocity fluctuations carried by wakes while propagating downstream. This accelerated the transition process and suppressed the separation bubble.