UNSTEADY SECONDARY FLOW IN AN ANNULAR COMPRESSOR CASCADE

Subject of the experimental investigations presented is the analysis of secondary flow in an annular compressor cascade. Focus lies on the so-called rotating instability. The investigations concentrate on the unsteady pressure field in the area of the blade tip clearance in order to get deeper understanding of the phenomenon of rotating instability. Therefore, transducers were mounted along the leading edges around the circumference of the cascade. This arrangement allows the determination of the coherence and the phasing between the transducers by the cross correlation via Fourier and wavelet transform. The results show the influence of the Mach number and the incidence angle on the onset of the phenomenon. Furthermore, a relation between the characteristic frequencies of the rotating instability to certain modal types can be stated. Moreover, the wavelet cross power spectrum suggests that the phenomenon is not continuously present within the spectra but shows an unsteady appearance.