12th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Rotating Instability (RI) induces noise, triggers blade vibrations and is a potential indicator for critical operating conditions in axial compressors. Despite numerous studies, the source of RI is not completely understood. The objective of the present study is to give further insight into the basic mechanism of RI by means of advanced Stereo High-Speed Particle Image Velocimetry (PIV) applied to an annular compressor cascade without clearance. In particular, results of the PIV measurements visualize the predominant flow mechanism corresponding to RI. The experiments were conducted at an inflow Mach number of Ma = 0.4. Additional reference sensors captured the time-resolved pressure fluctuations synchronously to the optical measurements. By using correlation techniques between the PIV flow field and the reference sensor data, discrete vortex structures corresponding to the RI modes could be identified and localized. As a verification of the PIV results, the steady PIV flow velocity vectors are compared to results from an oil flow visualization technique. Overall, the present investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without tip clearance.