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For a centrifugal compressor with volute, the flow field is circumferentially nonuniform because of the volute asymmetrical structure and leads to a circumferential difference in the tip leakage flow. In this work, the compressor performance and the casing wall static pressure distribution are measured, and the results are compared with the time-averaged results of the unsteady calculation to verify the reliability of the simulation. The results show a relationship between the tip leakage vortex trajectory and the high static pressure region in the diffuser, based on which a prediction model is established for the reverse propagation of pressure waves caused by a volute tongue. Influenced by the volute asymmetric structure, the trajectory, shape, and strength of the tip leakage vortex at different circumferential positions differs significantly. The tip leakage vortex trajectory affected by the high static pressure is more inclined to a circumferential direction because the tip leakage flow velocity flowing out of the suction surface is reduced, and the tip leakage flow with low velocity is subjected to the high-pressure gradient in a passage. Moreover, the tip leakage vortex breakdown in different passages differs significantly. A tip leakage vortex core more inclined towards the streamwise direction is more likely to break down than a tip leakage vortex core inclined towards the circumferential direction because of the larger reverse pressure gradient. [ABSTRACT FROM AUTHOR]

• Evolution trajectory of two-phase region is consistent with the LP1. • Evolution of the two-phase region in an impeller passage is revealed. • Prediction model for the two-phase region in impeller passage is established. In this study, unsteady numerical calculations of centrifugal compressors with volute were carried out. The unsteady evolution of two-phase regions and flow behavior in impeller passages were determined. The results show that the two-phase regions in impeller passages are governed mainly by the low static pressure strip LP1 on the casing wall. Meanwhile, the unsteady trajectory of a two-phase region is consistent with the trajectory of LP1. The unsteady evolution of a two-phase region undergoes two stages: In the first stage, it appears near the middle streamwise position and simultaneously expands to the leading edge (LE) and trailing edge (TE) of the blade. In the second stage, it shifts from the middle streamwise position to the LE of the blade and finally disappears. Moreover, based on the rotor enthalpy conservation, the prediction model for the formation of two-phase region in the impeller passage under different inlet conditions was determined. [ABSTRACT FROM AUTHOR]

Given the heightened requirements of understanding the flow structure under critical condition and improving flow control technique for the turbocharger compressor, further insight into the unsteady behaviors of spike-stall inception associated with tip leakage flow was vital. In this work, an unsteady full annular simulation of a centrifugal compressor coupled with experimental validations was carried out by using the Reynolds averaged Navier–Stokes technique. A spike-type stall in the impeller was determined with multiple criterion principles. Then, a dynamic mode decomposition procedure was applied to the numerical data to capture and visualize the dominant flow structure in both absolute and relative coordinate. The temporal and spatial development of coherent perturbations was reconstructed. Finally, based on the results of mode decomposition, a modified prediction model of vortex trajectory concerning the asymmetrical flow, which can determine the circumferential location of spike-stall inception, was put forward. The results indicate that the low-frequency perturbation associated with stall inception can be captured by the DMD approach under both absolute and relative frames with the perturbation frequencies of 0.44 RF and 0.5 RF, respectively. Under absolute coordinate, the stall inception can be decomposed into three patterns: stationary stall cell in the mean flow, propagated stall cell in a certain region associated with BPF and oscillated stall cell in the origin place with the stall frequency of 0.44 RF. Considering the flow reconstruction, the flow instability in the impeller is relatively stationary stall inception without a significant phase shift and the stall perturbation occurs at 120 ∘ circumferential location. The specific location of stall inception is influenced by the blade leading edge, which can be predicted by the prediction model of the vortex trajectory accurately. [ABSTRACT FROM AUTHOR]