Windage Loss and Flow Characteristics in Impeller Back Clearance of sCO2 Centrifugal Compressor

Abstract

Abstract In this paper, the windage loss and the flow characteristics in impeller back clearance divided into disk-type and shaft-type clearance for sCO2 compressor are investigated by numerical method. The effects of rotation speed, inlet pressure and disk-type clearance width on the windage loss and flow characteristics are analyzed in detailed. Through detailed numerical verification, realized k-ε turbulence model is finally selected, and all simulations are performed under the condition of the rotation speed of 20 ∼ 60 kr/min and inlet pressure of the 9 ∼ 12 MPa, respectively. The study results show that windage loss in disk-type clearance increases with rotation speed and inlet pressure increasing, and the influences of rotation speed on windage loss are more obvious than that of inlet pressure. Both the flow instability and more vortexes at inlet become main reasons why windage loss increases. The relative deviations of 105% ∼ 217% between Daily’s loss model results and simulated results indicate that loss model is not applicable to predict the windage loss. What more, the windage loss in shaft-type clearance is basically increases linearly with the rotation speed and inlet pressure increasing. The proportion of windage loss in shaft clearance to total loss ranges from 9% to 16%, which indicates the windage loss in shaft-type clearance can be neglected for the preliminary design on sCO2 compressor. In addition, the maximum relative deviation of 2 % for the leakage model can be completely applicable to the design of sCO2 compressor. Disk-type clearance width has significant influence on both loss and flow characteristics. The windage loss in disk-type clearance decreases with the clearance width increasing, and the variation rate of windage loss increases as the clearance width increases. Larger width makes number of vorticities decrease at turning angle and changes flow direction easily, which is favorable to decrease windage loss. Finally, Daily’s loss model is modified and the modified loss model is validated. The maximum relative deviation of 17% for modified loss model is completely accepted, which indicates the modified loss mode can substantially improve accuracy of calculating windage loss in the impeller back clearance of sCO2 centrifugal compressor.