Impact of operating conditions on rotor/stator interaction of a high-pressure ratio centrifugal compressor

The current design trend of centrifugal compressors is aimed at obtaining compact machines with high pressure ratios and performance. This leads to high circumferential speeds and lighter components, thus increasing static stresses and dynamic forcing due to rotor/stator interactions. Therefore, the aeromechanical characterization of these machines is a fundamental step of the design chain. This paper presents an in-depth aeromechanical study of a high-pressure ratio centrifugal compressor using CFD. Firstly, the computational setup is validated against the experimental data; then, the same numerical setup is used to characterize the aeromechanical interactions between the impeller and the upstream and downstream static components. The URANS simulations are carried out at three different operating points (near stall, design, near choke), and the unsteady flow field is time and space decomposed showing higher forcing functions at near stall and near choke conditions with respect to the design point, as confirmed by the experimental acquisitions. The presented results highlight the importance of extending the aeromechanical evaluations to different operating points in order to avoid unexpected vibration responses when operating at off-design conditions. Finally, by virtue of an acoustic post-processing techniques, the unsteady pressure coupling in the inter-row region is analyzed to discern the main sources of the overall unsteady interaction.