The role of shaft-speed oscillation on the instability behavior of transonic radial compressor

Abstract A dynamic model of the free-spool compression system is established to investigate the effects of rotational speeds oscillation on the surge characteristics and behaviors. Simulation results show better agreement with the experimental data compared to the fixed-spool simulation, which confirms the importance of introducing rotor dynamics into surge modeling. The mechanism of the prolonged surge cycle is presented, as well as an overall comparison and explanation of discrepancies in surge characteristics between different operating speeds and design cases. It is pointed out that the relative position of the averaged deceleration line and the surge line is critical in leading to the discrepancies. Further perturbation analysis concerning the effects on the surge limit suggests that reducing the rotational inertia of the spool may enhance the system stability under certain circumstances, which can be evaluated by the speed variation contribution parameter (SVC). The results may further contribute to the design of surge control system.