Study on boundary layer in a rotating channel

本项目的目的是弄清科氏力对旋转通道尾、前缘壁面二维边界层发展的影响，以及对展向/横向固定圆柱后湍流尾迹的影响，并提供旋转湍流边界层数值模拟所需的时均量和湍流量的大量数据。为此，设计了旋转风洞，并进行了定量实验，实验结果表明：旋转通道内前缘边界层发展受到促进，后缘边界层发展受到抑制。二维边界层保留在后缘，而三维对应于泰勒-戈特勒型纵向涡产生在前缘。在较高的旋转数下，在尾侧观察到再层化现象。雷诺应力数据与雷诺应力方程预测的结果定性一致，在展向固定圆柱后的旋转尾迹中，由于主流的横向速度梯度和瞬时科里奥利力引起的流动不稳定性，脱落涡的破裂发生在比非旋转尾迹低的雷诺数下。对于展向小展弦比圆柱后的湍流尾迹，平均速度和湍流强度的分布关于尾迹中心线是不对称的。尾迹是一个非常复杂的三维流动，因为圆柱周围的三维分离和旋转通道的顶壁和底壁上的边界层中的二次流。

The objective of project is to make clear the effects of Coriolis force on the developing two-dimensional boundary layer on trailing and leading side walls of a rotating channel, on the turbulent wake behind a fixed spanwise/transverse circular cylinder, and to offer many data on time-mean and turbulent quantities which are desirable in numer-ical simulation of rotating turbulent boundary layer. Thus, a rotating wind tunnel was designed, and quantitative experiments were performed.The experimental results indicate that the development of boundary layer on the leading side in rotating channel is promoted and suppressed on the trailing side. Two-dimensionality of the boundary layer is preserved on the trailing side, while three-dimensionality corresponding to Taylor-Goertler type longitudinal vortices is generated on the leading side. At higher rotation number, the phenomenon of relaminarization was observed on the trailing side. Reynolds stresses data agreed qualitatively with that predicted from the Reynolds stress equations with rotation.In a rotating wake behind a fixed spanwise cylinder, breakdown of shed vortices occurs at lower Reynolds number than in a non-rotating wake because of a transverse velocity gradient of primary flow and a flow instability due to instantaneous coriolis force. For a turbulent wake behind a low aspect ratio cylinder located spanwise, profiles of mean velocity and turbulence intensity are not symmetrical about the wake centerline. The wake is a very complex three-dimensional flow because of a three-dimensional separation around a cylinder and a secondary flow in a boundary layer on the top and bottom walls of a rotating channel.