Effects of pulsating backpressure on performance of stability of a centrifugal compressor

A centrifugal compressor is operated at unsteady exit conditions in many scenarios. The performance of compressor stability is notably altered by the unsteady conditions, but reasons for the influence have not been understood yet. This paper studies the mechanism of pulsatile backpressure on the stability performance of a centrifugal compressor. Firstly, the aerodynamic stability is discussed in the compressor unit by 3-D unsteady CFD method. A street of vortexes is generated near shroud in the impeller inducer at both constant and pulsating conditions, which is caused by the rolling-up of shear layer between the tip clearance flow and main flow due to K-H instability. But the rolling-up of the shear layer is evidently depressed by the pulsating backpressure. Consequently, the secondary flow and blockage in the impeller are alleviated, and hence the aerodynamic stability of the compressor is benefited. Next, the dynamic stability is studied in the compression system theoretically via Lyapunov function in perspective of energy balance. The results show that both the characteristics of compressor and throttle are influenced by the pulsating condition. Specifically, the characteristic of compressor becomes steeper at pulsating condition and thus less energy is added into the compression system. On the other hand, the characteristic of throttle also becomes steeper, thus the capability of energy-damping in the system deteriorates. The dynamic instability of the system is determined by the trade-off between these two influences. Finally, the route of the influence by the pulsating backpressure on the compressor stability is drawn according to both the aerodynamic instability of the compressor component and dynamic instability of the compression system.(c) 2022 Elsevier Masson SAS. All rights reserved.