12th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
The path to instability of a small centrifugal turbo-compressor included in an air supply system developed by Liebherr-Aerospace was experimentally investigated thanks to high-frequency unsteady static pressure sensors. At the lowest speed line, rotating stall is observed both at impeller inlet and vaned diffuser inlet. It is characterized by one stall cell rotating at 6.4% of the impeller speed. At higher rotational speeds, the compressor experiences deep surge. The surge frequency decreases as the rotational speed increases and as the downstream volume increases. The peak-to-peak pressure amplitude increases as the rotational speed increases but do not depend on the downstream volume. A detailed analysis of the instability onset was performed thanks to Fourier and wavelet transforms showing that the instability inception is disclosed by pressure spikes. Nevertheless the spikes cannot be considered as precursors but as the embryo of the developing instability, which jeopardizes the chances of a control system to damp the perturbation.