Shear Flow Through a Cascade

Abstract

SummaryWhen a flow with a non-uniform velocity passes through a cascade, the blades impose on each layer of the flow local pressure changes which are roughly proportional to the dynamic head in the layer. This results in local pressure differences which, within the blade passages, produce rotational secondary flows and which also cause overall spanwise accelerations and displacements. These effects are analysed for frictionless flow by treating the blade row as an actuator plane whose outlet angle is determined by the secondary velocities in the blade passages.At low outlet angles or large deflections the secondary flows effectively control the downstream flow angles. When the outlet angle is large the displacement effect can result in downstream flow angles of opposite sign to those induced by the secondary flow alone.Measurements on cascades with small spanwise variations induced in the approaching stream confirm the main predictions of the first order theory.