Analysis of rotor tip clearance loss in axial-flow turbines

Abstract

Tip clearance flow is a major contributor to the losses in axial flow turbines. Tip shrouding reduces the extent of this loss at the expense of more structural complexity and increased centrifugal blade stresses. Recent technological advance in the area of active clearance control promises to minimize the tip clearance loss without the adverse tip shrouding effects. Due to complexity of rotor tip flows, a comprehensive tip clearance loss model that accounts for the tip shape, relative wall motion, tip loading, and stage characteristics has not yet been developed. In the present paper, the rotor tip clearance flow is aerothermodyn amically analyzed and a loss model is presented that includes the above-mentioned effects. Tip leakage discharge coefficient and the stage loading factor are taken as modeling parameters. Finally, earlier tip clearance loss models are reviewed and comparisons are drawn with the present work.