Uniformly rotating flow in a straight duct followed by a contraction: experimental and theoretical study of the mean flow

Abstract

We study the mean dynamics of a radially confined, uniformly rotating flow of high Reynolds number. The duct geometry consists of a portion of constant cross-section followed by a final contraction, downstream of which the flow exhausts as a swirling jet. The duct flow is investigated by Stereoscopic PIV. To understand the specific effect of the contraction, we also consider the case where it is replaced by a straight duct portion. These experimental results are compared with a simulation of axisymmetric steady flow at a moderate Reynolds number. Good agreement is obtained between the two methods. Both show that the flow is strongly influenced by the contraction when it is subcritical with respect to axisymmetric Kelvin waves. In that regime, no vortex breakdown is found inside the duct. Instead, large-amplitude standing waves of positive azimuthal vorticity are observed.