Loss mechanisms in turbine tip clearance flows

摘要: Numerical simulations of tip clearance flow have been carried out to define the loss generation mechanisms associated with leakage in unshrouded axial turbines. Mixing between leakage, which takes form a strong embedded streamwise vortex (uθ/ux ≥ 1 core), and mainstream is found be main source loss. Vortex line contraction, consequent core expansion, also breakdown, are identified as two important that determine mixing Because these dynamic features, behavior different from conventional view effect pressure level on nonuniform flows. More specifically, it shown, through control volume arguments axisymmetric computations, strongly swirling passes rise, mixed-out can either decrease or increase, latter occurring if deceleration becomes large enough initiate breakdown. It further shown vortices turbines experience rises cause The distribution losses illustrated examination turbine blades, one designed forward loaded an aft tip. computations show 16% difference two, due lower rise encountered by vortex, hence breakdown losses, blade. Other computational experiments, effects blade loading, incidence, solidity, consistent ideas developed about Thesis Supervisor: Edward M. Greitzer Title: H.N. Slater Professor Aeronautics Astronautics Choon S. Tan Senior Research Engineer Steven G. Gegg Manager, Turbine Aerodynamics, Rolls-Royce Corporation