Scaling Laws at Stall in an Axial Compressor with an Upstream Perturbation

An experimental campaign has been conducted to assess the effect of total pressure inlet distortion on a single stage axial compressor. Different grid sectors have been installed in front of the inlet of the compressor to generate the distortion. Pressure measurements and particle image velocimetry have been used to characterize the impact of the distortion on the flowfield and the performance of the compressor. The broad range of porosity and angular extension of the grid sectors has allowed identifying four different flow regimes characterised by a different response of the compressor. In particular, the low porosity introduces flow regimes which have been never encountered in typical distortion tests restricted to high-porosity grids. In two of these regimes, it has been possible to identify a new scaling of the stall margin versus a new distortion index based on more solid physical ground than already existing indices such as the DC60. The experiments have also shown that for each of these four flow regimes behind the grid different rotating stall features (spike stall or modal stall) appear. A scaling of the stall dynamic has been finally provided thanks to analysis of unsteady casing static pressure signals acquired during the stall transient.