Centrifugal Compressor Instability and the Reverse Propagation Mechanism in Diffusers

At low flow rates, centrifugal compressors often experience aerodynamic instabilities, posing a crucial concern for gas turbine engineers. This study focused on a standard centrifugal compressor and investigated its aerodynamic behavior through numerical simulations in both steady and unsteady full-annulus states. Additionally, it analyzed diffuser stability by evaluating the signals associated with rotating stall. Results indicated that, as the flow rate decreases and the flow shifts downstream in the full-cycle model, the non-uniformity of the Mach number in the circumferential direction near the blockage region increases from 8.13% to 25.52%. Under the design condition, the circumferential non-uniformity rises from 15.18% to 24.12%. When the compressor becomes unstable, the centrifugal impeller exhibits rotational instabilities with a disturbance frequency of 1304.61 Hz, corresponding to 23.95% of the blade passing frequency. The conclusions of this study provide fresh insights into unsteady flow characteristics in centrifugal compressors and offer practical guidelines for enhancing the operational stability of microturbine units.