Structure and Decay of Secondary Flow in the Downstream of a Cascade

Abstract

An experimental investigation has been done on trailing and passage vortices downstream of a decelerating cascade. Hot wire traverses gave distributions of secondary flow velocities and streamwise vorticities at four axial locations. A spanwise distribution of passage circulations per unit span agrees well with a prediction by an inviscid classical secondary flow theory. The trailing vortex is well approximated by a vortex sheet immediately downstream of the blade, beginning to roll up at the position of maximum circulation per unit span, It develops into an almost axisymmetric vortex tow chord lengths downstream. The trailing vortex decays faster in the vicinity of the blade trailing edge but more slowly far downstream, than the passage vortex does. The experimental trailing vortex is generated very far away from an endwall as compared with a theoretical position, exerting significant influences on the maximum underturning and the pitch-averaged streamwise vorticity in the main flow region.