Abstract: The hub treatment with a circumferential groove was tested on the stator hub and compared with the casing treatment over the rotor tip for a single stage axial flow compressor. The 3D flowfield at the downflow of stator blade rows, particularly its endwall flowfield in optimum operation and near stall state were measured by a microfive-hole probe. It was shown that stall margin can be improved , even if the onset of stall is at the rotor tip first. The relation between the mechanism of stability extension and stall transfer was obtained. A physical modle of effect of circumferential inducing velocity on the endwall secondary flow is proposed. The mechanism to extend stability of circumferential grooved hub treatment was also analyesd with more details.

Key words: casing treatment, unsteady flow, compressor