MEASUREMENTS OF THE TIP CLEARANCE FLOW FOR A HIGH REYNOLDS-NUMBER AXIAL-FLOW ROTOR

A high-Reynolds-number pump (HIREP) facility has been used to acquire pow measurements in the rotor blade tip clearance region, with blade c hord Reynolds numbers of 3,900,000 and 5,500,000. The initial experime nt involved rotor blades with varying tip clearances, while a second e xperiment involved a more detailed investigation of a rotor blade row with a single rip clearance. The flow visualization on the blade surfa ce and within the pow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the tr ailing edge and then turns in the circumferential direction near the c asing, moving in the opposite direction of blade rotation. Flow visual ization also helps in establishing the trajectory of the tip leakage v ortex core and shows the unsteadiness of the vortex. Detailed measurem ents show the effects of tip clearance size and downstream distance on the structure of the rotor rip leakage vortex. The character of the v elocity profile along the vortex core changes from a jetlike profile t o a wakelike profile as the tip clearance becomes smaller. Also, for s mall clearances, the presence and proximity of the casing endwall affe cts the roll-lip, shape, dissipation and unsteadiness of the tip leaka ge vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associate d with high losses.