Secondary Flows in Cascades of Twisted Blades

Abstract

Squire and Winter's definitive paper on secondary flow treats the situation of a nonuniform velocity profile through a cascade of blades whose properties—i.e., geometry—are uniform with height. The analysis focuses on the flow in a single passageway between blades. Tsien has treated the special case of uniform flow through a cascade of blades whose properties vary as a function of blade height. He uses a classical Prandtl lifting line analysis. Using a conceptual model similar to that of Squire and Winter, a general analysis is carried out to determine the perturbation or secondary flow resulting from a nonuniform velocity profile passing through a cascade of blades whose properties vary as a function of blade height. The general result reduces exactly to the special form of Squire and Winter and also gives a result quantitatively and qualitatively equivalent to that of Tsien. Experimental measurements in a cascade give results indicating the pertinence of the analysis except in the regions where viscous stresses invalidate the assumptions.