Flow measurements near the open surfaces of single circumferential grooves in a low-speed axial compressor

Circumferential grooves (CG) is an effective method to enhance the compressor stall margin with minor efficiency disturbances. The interaction between the groove and the blade passage is found to be responsible for the stall margin improvement (SMI) by many studies. The momentum transport across open surface of an individual groove could be an indicator to assess its effectiveness. These findings are all derived by numerical means. Two single grooves are chosen as the examples to demonstrate the needs of the experimental validation. In experiments, one groove, CG5 at 27% axial chord, produced less SMI than the other one, CG7 at 43% axial chord. Yet, many CFD simulations predicted just the opposite. In order to validate the numerical simulations, detailed flow structures are needed near the open surfaces of the casing grooves. However, such experimental results are still missing due to the difficulties of measurement, especially for the flow measurement inside the grooves. Aiming at providing reasonable experimental results for these casing grooves, a measuring technique is proposed in this paper. A special algorithm is utilized to obtain the time-averaged magnitudes of velocity components by using three hot-wire probes. The groove-passage interaction is recorded using the fluctuations of each velocity component and the frequency spectrum. Intensive interaction is detected for CG7. The experimental results demonstrate that the flow interaction between the groove and blade tip is crucial to the stability enhancement.