저널 래버린스 실이 임펠러 추력 및 누설에 미치는 영향

Abstract

In recent years, turbomachinery pursue high speed operations in compact volume to achieve high specific power. An impeller operating at high rotating speeds increases the compression ratio and results in significant axial thrust forces which must be balanced with balance piston or thrust bearing. A leakage flow flowing through Labyrinth seals located in the gap between the rotor and stator parts also influences the magnitude of the thrust forces. This study develops a predictive model of an impeller coupled with a labyrinth seal to predict the resulted axial thrust force. Firstly, a comparison between the predicted cavity pressure and leakage to the published test data validates the bulk-flow model of the labyrinth seal used in the paper. Then the coupled model of the impeller to the labyrinth seal is verified by comparison of the predicted pressure distributions and leakage flow rates to those from CFD analyses using the k-ε turbulence model. Additionally, the study reports the effects of the labyrinth seal design, operating speed, and lubricant type on the axial thrust force and the leakage flow rate. The results show that the labyrinth seal decreases the leakage flow rate but increases the axial force, implying the need of trade-off between the impeller axial force and leakage flow rate. As the gap between the impeller and casing wall decreases, both the impeller axial force and leakage flow rate decrease. The impeller axial force and the leakage flow rate predicted using refrigerant gas are smaller and less sensitive to the change of the labyrinth seal design when compared to those predicted using air.