Unsteady two-phase region evolution of SCO₂ centrifugal compressor

In this study, unsteady numerical simulations of centrifugal compressors with and without volute were carried out. The unsteady two-phase region evolution in the centrifugal compressor is obtained. Large coherent perturbations were revealed by the decomposition of the transient flow data using the dynamic mode decomposition (DMD) approach. The results imply that because of the low static pressure strip LP1, the two-phase region presents a triangular distribution at the blade leading edge (LE) of the pressure surface (PS) side in one impeller rotation period for both a low flow rate and the design flow rate. At a high flow rate, the two-phase region displays a double triangle distribution on the PS side of the blade LE, which is correlated with the low static pressure strips LP1 and LP2. The maximum two-phase region on the PS side of the LE of the blade occurs downstream of the LP1 position. The two-phase region in the tip clearance is deflected along the LP1 trajectory. DMD analysis shows that there are four modes related to the two-phase region in the tip clearance: mean flow mode with a frequency of 0 Hz and three modes with frequencies of 0.5, 1.0, and 1.5 BPF respectively. Furthermore, the circumferential local perturbation region of these four modes has the same deflection trajectory as that of LP1.