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

在旋转通道（如涡轮增压器的叶轮通道）中的边界层流动分别由壁面曲率和系统旋转引起的离心力和科里奥利力控制，离心力和科里奥利力通过抑制或促进湍流运动来控制边界层的发展。虽然人们对静止状态下凹、凸表面上的湍流边界层作了许多研究，但在旋转坐标系中科氏力的综合作用却很少涉及，本项目在中心线曲率半径分别为1, 000 mm和2, 000 mm的通道中，测量了凹表面附近的速度和湍流强度，并对实验结果进行了分析。主要结果如下：（1）垂直于壁面的科里奥利力促进了Goertler不稳定性的发生，促进了层流向湍流的转变，而壁面的科里奥利力则推迟了层流向湍流的转变。(2)当基于动量厚度的雷诺数超过临界值时，无论旋转速率和主流速度的差异如何，都会发生过渡。(3)在负旋转速率下，波动分量被抑制，并且进一步减小产生不同类型的不稳定性。

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.