D213 主流乱れによる境界層遷移 : 水素気泡法による観察

概要

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Boundary layer transition subjected to free stream turbulence has been investigated using the stereo PIV technique for the hydrogen bubbles in water flow. The disturbances of the free stream turbulence generate streamwise elongated regions of low streamwise velocity, so called streaky structures, in the boundary layer and this structures develop downstream and breakdown to turbulence with spanwise waviness motions. This study is focused on the investigation of the lift-up mechanism that explains in the non-modal theory that the wall-normal velocity disturbance in a shear flow induces the large streamwise velocity disturbance. The flow visualizations with hydrogen bubbles directly show exist of the lift-up mechanism in the boundary layer. Furthermore, the stereo PIV using two synchronized video cameras gives instantaneous time-spanwise distributions of the streamwise velocity and the wall-normal velocity. This information makes the streaky structure visible in the velocity fields and shows negative correlation between u and v components assuring the non-modal theory.
2000-07-25