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Within the present paper the development and interaction of secondary flow structures at different hub clearance gaps at high blade loadings are investigated. Three-dimensional numerical computations were carried out at three levels of hub clearance, ranging from zero to 3% of blade chord. Experimental results at 1% and 3% chord hub clearance were obtained to asses the validity of the numerical predictions. The experimentally and numerically obtained results provide a detailed picture of the development, the interaction of secondary flow structures and the influence of clearance flow for high blade loading. Therefore the time averaged flow features obtained from the experimental test rig and from numerical simulations are compared. In addition this investigation tends to explain the phenomenon of rotating instability for this compressor stator at a specific operating point and different hub clearance gaps by analyzing the secondary flow structures in the leading edge region at the hub.

The unsteady endwall pressure distribution is investigated by means of highly resolved pressure measurements and numerical simulations in an axial compressor stator exhibiting the phenomenon of rotating instability. The endwall flow has been observed to play an important role in the inception of rotating instability. The statistical properties of the measured pressure fluctuations at the hub endwall of the axial compressor stator are compared for a series of blade loadings. The results allow conclusions about the location of regions being closely connected to the unsteady dynamics related to the rotating instability phenomenon. Furthermore the operating points with detected rotating instability are compared with unsteady numerical results.