Transition mechanism, prediction, and control of crossflow field

Through systematic investigation concerning the crossflow dominant boundary layer transition, the complicated transition mechanism was clarified experimentally. Namely, transition starts with stationary streamwise vortex (crossflow vortex) generation. This is called 'primary instability'. Then, primary instability induces three unsteady instabilities, F(sub 1), F'(sub 1)(relatively low frequency), F(sub 2) (relatively high frequency). F(sub 1) travels to crossflow direction, F(sub 2) travels to streamwise direction, and F'(sub 1) travels to the opposite direction with F(sub 1). It seems to be that F(sub 2) enhances the transition into full turbulent. Taking into consideration of such flow mechanism, a prediction method has been developed by introducing C(sub 1), C(sub 2) which is valid in general three-dimensional boundary layer transition. Knowing the threshold value for critical condition either by experimentally, or numerically, it is possible to predict transition onset simply calculating potential flow information. A unique and practical selective suction method to delay the transition with less suction power. It was possible to delay the transition with one third of the power of uniform suction.
資料番号: AA0032827009
レポート番号: NAL SP-54