Three-dimensional flowfield downstream of an axial-flow turbine rotor

A systematic and comprehensive investigation was performed to provide detai led data on the three-dimensional viscous now phenomena downstream of a mod ern turbine rotor and to understand the pow physics such as the origin, nat ure, development of wakes, secondary flow, and leakage flow. The experiment was carried out in the Axial Flow Turbine Research Facility at Pennsylvani a State University, with velocity measurements taken with a three-dimension al laser Doppler velocimetry system. Two radial traverses at 1 and 10% of c hord downstream of the rotor were performed. Sufficient spatial resolution was maintained to resolve blade wake, secondary flow, and tip leakage flow. The wake deficit is found to be substantial, particularly at 1% of chord d ownstream of the rotor. At this location, negative axial velocity occurs ne ar the tip, suggesting flow separation in the tip clearance region, Cross c orrelations are mainly associated with the velocity gradient of the wake de ficit. Radial velocities, in the wake and the endwall region, are found to be substantial. Two counter-rotating secondary flows are identified in the blade passage, with one occupying the half-span close to the casing and the other occupying the half-span close to the hub. The tip leakage flow is re stricted to 10% immersion from the blade tip. There are strong vorticity di stributions associated with these secondary flows and tip leakage Bow. The passage-averaged data are in good agreement with design values.