Investigation of Stall Inception Behavior in a Centrifugal Compressor with Bent Pipe/Volute Coupling Effect

Abstract

The centrifugal compressor typically has a bent inlet pipe and volute due to the engine equipment installation, leading to the existence of asymmetric structures in both the inlet and outlet of the impeller. Under the coupling effect between the bent inlet pipe and outlet volute, the onset time and the circumferential position of the stall inception, as well as the stall development process, will be influenced. In this work, three centrifugal compressor models are investigated. The M0 model has the straight inlet pipe, and the M1 and M2 models have bent inlet pipes with different installation angles between the bent pipe and volute tongue. Unsteady numerical simulations are carried out, and the static pressure distributions of the casings are compared between the experiment and unsteady time-averaged results, to validate the unsteady simulations. Based on the casing static pressure comparison, unsteady simulations of the stall process are carried out for three models. Results show that the influence of the bent pipe on the stall process is smaller than that of the volute. Therefore, the circumferential onset position of stall inception is always located at the circumferential position of the pressure peak induced by the volute, irrespective of the pipe installation angle. The onset times of stall inception for the bent pipe models are earlier than those of the straight pipe models. When the low total and static pressure region of the bent pipe’s inner wall acts on the same position of the pressure peak region induced by the volute at the impeller inlet (corresponding to model M1), the momentum of incoming flow reduces at this position; thus, the capability of resistance to reverse pressure gradient decreases, which causes an earlier stall inception onset. In contrast, when the high total and static pressure region of the bent pipe outer wall acts on the same position of the pressure peak region induced by the volute at the impeller inlet (corresponding to model M2), the stall inception onset time will be delayed. Meanwhile, the stall development process of M2 is faster than that for M1. In the application of an inlet bent pipe, the installation angle of model M2 should be adopted to delay the stall inception onset and improve compressor performance.