In recent years, supercritical carbon dioxide Brayton cycle has attracted much attention for its high cycle efficiency and compact mechanical structure. The supercritical carbon dioxide centrifugal compressor plays a vital role in the system. For supercritical carbon dioxide centrifugal compressor with volute, the asymmetric structure of volute induces circumferential non-uniform distribution of upstream flow field, which will inevitably affect supercritical carbon dioxide condensation in the impeller. In this work, unsteady simulations for centrifugal compressors with volute were carried out. The supercritical carbon dioxide condensation was determined by dimensionless supercooling coefficient. The condensation characteristics of supercritical carbon dioxide centrifugal compressor with volute were analyzed in detail and the reasons were explained. Firstly, the influence of low static strip on impeller flow field induced by low static pressure near volute tongue was presented. The non-uniform flow field distribution in the impeller passages under the influence of asymmetric volute structure was obtained by studying the velocity distortion in the impeller passages. Then, the velocity distortion analysis was performed by discussing the unsteady velocity distribution near the blade surface. Finally, the reason of condensation on the blade leading edge and tip clearance was sought with the analysis of flow in the passages at the impeller inlet and tip leakage flow. The results show that for a centrifugal compressor with volute, the supercritical carbon dioxide condensation appears not only on the suction surface of the blade leading edge, but also in some impeller passages, on the pressure surface of the blade leading edge and in the tip clearance under the design condition. The asymmetric structure of the volute induces a low static pressure zone near the volute tongue which propagates upstream forming a low static pressure strip. Compared with other circumferential positions, the impeller passage flow velocity in the low static pressure strip is higher, which results in the supercritical carbon dioxide condensation appears on both sides of blade LE and in the passages. The tip leakage flow of the blade in low static pressure strip is distorted, and the distorted position is close to the leading edge of blade. The tip leakage flow near the blade leading edge moves along the chord direction, and then flows through the tip clearance to the adjacent impeller passage along with the tip leakage flow near the 50% chord. The convergence of tip leakage flow at 50% chord leads to the increase of flow velocity in tip clearance, which leads to supercritical carbon dioxide condensation in tip clearance. The asymmetric structure of volute has a crucial influence on the flow balance and condensation characteristics of supercritical carbon dioxide centrifugal compressor.


Non-Uniform Two-Phase Flow of Supercritical Carbon Dioxide Centrifugal Compressor

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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