Study of Stability and Instability of Boundary Layer Flow on Rotating Curved Wall

叶轮等旋转流道中的边界层流动分别受壁曲率和系统旋转的离心力和科里奥利力的作用，通过抑制或促进湍流运动来主导边界层的发展。对定常条件下凹面或凸面上的湍流边界层进行了大量的研究，但对旋转坐标系中科里奥利力的综合效应研究甚少。在本课题中，测量了不同旋转条件下，中心线曲率半径分别为1000 mm和2000 mm的通道内凹面附近的速度和湍流强度。(1)垂直于壁面的科里奥利力促进了Goertler不稳定性，促进了流动从层流到湍流态的转变，而从壁面施加的Coriolis力则延迟了转变。(2)当基于动量厚度的雷诺数超过某一临界值时，发生转变，而与旋转率和主流速度的差异无关。(3)在负转速下，脉动分量被抑制，进一步减小将产生不同类型的不稳定。

The boundary layer flows in rotating channels such as impeller passages of turbomachinery are dominated by the centrifugal and Coriolis forces due to the wall curvature and system rotation, respectively, which predominate the boundary layer development by suppressing or promoting the turbulent motion. Though many studies have been made about the turbulent boundary layer over a concave or convex surface in the stationary state, the resultant effects due to the Coriolis force in the rotation frame have scarecely been made.In the present project, the velocity and turbulent intensity are measured near the concave surface in channels whose centerline radii of curvature are 1,000mm and 2,000mm, respectively, for different rotating conditions.Main results can be summarized as follows ;(1) The Coriolis force exerting normally toward the wall promotes the Goertler instability and advances the transition of the flow from laminar to turbulent state, but that exerting from the wall delays the transition.(2) The transition occurrs when the Reynolds number based on the momentum thickness exceeds a critical value, regardless of the difference in the rotation rate and the main flow velocity.(3) At negative rotation rates the fluctuating component is suppressed and a further decrease generates a different type of instability.