Investigation of Transition in 3D-Boundary Layer

通过3年的研究，我们成功地阐明了复杂的三维转变机制。特别是后掠翼边界层的过渡机制如下：顺流静止涡系统开始作为主要不稳定因素出现。该定常涡诱导了两种不同频率模态的非定常波不稳定性。高频二次不稳定性被认为是湍流过渡的关键序列。此外，我们成功地延缓了后掠翼三维边界层从层流到湍流的过渡，并证实了后掠翼摩擦阻力的减小。通过在静止涡位置选择性地吸入低动量流，我们成功地将过渡延迟了至少1/3的吸力体积与均匀吸力相比。

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.