Measurements of low reynolds number flow in rotating channels

The impact of Coriolis forces on low Reynolds number decelerating flows is studied by means of time resolved Particle Image Velocimetry in a 6 degrees diverging channel. Measurements are made with a high speed camera and a continuous light source rotating at the same speed as the rotating channel. This allows a direct and accurate recording of the time varying relative velocity. The Reynolds number can be varied from 3 000 to 30 000 in combination with a change of rotation number between 0.0 and 0.33. These values are characteristic for the flow in the blade passage of centrifugal impellers used in micro gasturbines. Increasing rotation stabilizes the flow on the suction side. The peak turbulence intensity shifts away from the wall with a small increase of its amplitude. The turbulence intensity on the pressure side increases its peak value and concentrates closer to the wall when increasing rotation. Instantaneous flow field analyses indicate that elongated vortical structures characterize the boundary layer in the stationary case and on the pressure side of the rotating channel. Isotropic vortices develop relatively distant from the wall on the suction side. Their position and size are tracked in time by means of a wavelet analysis.