Secondary Flow Effects on Gas Exit Angles in Rectilinear Cascades

Abstract

This paper considers the problem of secondary flow generation in a blade passage resulting from the presence of end-wall boundary layers at the passage inlet. These boundary layers are represented by a vorticity normal to the inlet flow, which takes on a streamwise component as the fluid is turned in the passage. Finite-difference solutions for this streamwise vorticity at the passage exit are found for steady, inviscid, incompressible flow about thin, circular arc blades of moderate turning. From these, the secondary flow stream functions, and subsequently outlet angle changes due to secondary flow are computed. Calculations were made for a wide range of blade spacings, chords and lengths, inlet boundary layer thicknesses and gas inlet and leaving angles. A careful study of these results led to the development of a simple but remarkably consistent correlation between outlet angle change due to secondary flows and the cascade geometry. While somewhat limited in its applicability, the correlation gives the axial turbomachine designer a very simple method of assessing the spanwise variation of gas leaving angles resulting from secondary flows at the blade exit.