Secondary flow effects in relatively narrow channels

Abstract

Secondary flow effects were discussed in numerous papers at the past ISAIF Symposia, mainly in connection with turbine or compressor cascades^[1]. This paper will complement these papers by looking at the problem from the channel (or blade passages) geometry point of view. If we describe as secondary flows any flows in planes perpendicular to the main flow direction, then there are at least three kinds of secondary flows in a typical turbine rotor cascade:

• -secondary flows of the 1^st kind, generated by centrifugal forces in closed curved channels,

• -secondary flows of the 2^nd kind, generated by interacting boundary layers, mainly in corners (this will include even the horseshoe vortices),

• -secondary flows due to mass inflow through the tip clearance.

Quite often all the secondary flow vortices merge downstream into a passage vortex with a non-negligible contribution to the channel (cascade) losses, and it is worth investigating the individual contributions to these losses to take them into account in the design procedure.