Tip-clearance and secondary flows in a transonic compressor rotor

The purpose of this paper is to investigate tip-clearance and secondary flo ws numerically in a transonic compressor rotor. The computational method us ed is based on the numerical integration of the Favre-Reynolds-averaged thr ee-dimensional compressible Navier-Stokes equations, using the Launder-Shar ma near-wall k-epsilon turbulence closure. In order to describe the flowfie ld through the tip and its interaction with the main flow accurately, a fin e O-grid is used to discretize the tip-clearance gap. A patched O-grid is u sed to discretize locally the mixing-layer region created between the jetli ke flow through the gap and the main flow. An H-O-H grid is used for the co mputation of the main flow. In order to substantiate the validity of the re sults, comparisons with experimental measurements are presented for the NAS A_37 rotor neat, peak efficiency using three gl ids (of 10(6), 2 X 10(6), a nd 3 X 10(6) points, with 21, 31, and 41 radial stations within die gap, re spectively). The Launder-Sharma k-epsilon model underestimates the hub corn er stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap, and the mixing downstream of the rotor. The computation al results indicate the presence of an important leakage-interaction region where the leakage-vortex after crossing the passage shockwave, mixes with the pressure-side secondary flows. A second trailing-edge tip vortex is als o clearly visible.