The Influence of Sweep on Axial Flow Turbine Aerodynamics in the Endwall Region

Sweep, when the stacking axis of the blade is not perpendicular to the axi-symmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. In a previously reported study, the authors demonstrated that sweep leads to an inevitable increase in mid-span profile loss. In this paper, the influence on the flowfield close to the endwalls is investigated. Experimental data from two linear cascades, one unswept, the other swept at 45 degrees but having the same overall turning and mid-span pressure distribution, are presented. It is shown that sweep causes the blade to become more rear-loaded at the hub and fore-loaded at the casing. This is further shown to reduce the penetration of the secondary flow at the hub, and to produce a highly unusual secondary flow structure, with low endwall over-turning, at the casing. A computational study is then presented in which the development of the secondary flows of both blades is studied. The differences in the endwall flowfields are found to be caused by a combination of the effect of sweep on both the endwall blade loading distribution, and on the bulk movements of the primary irrotational flow.