Investigation of Transition in 3D-Boundary Layer

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Through 3 years of this research project, we have succeeded to clarify the complicated 3D transition mechanism. Especially, swept wing boundary layer transition mechanism is as follows : Streamwise stationary vortex system starts to appear as the primary instability. Unsteady wave instabilities of two different frequency modes are induced by this stationary vortices. High frequency secondary instability is considered to be the key sequence for the turbulent transition.Moreover, we succeeded in delaying a transition from laminar to turbulent in 3D-boundary layer on swept-wing effectively, and confirmed the reduction of the frictional resistance of swept wing. By sucking the low momentum flow selectively at the position of stationary vortices, we have succeeded to delay the transition with at least 1/3 of the suction volume compared with the uniform suction case.