EXPERIMENTAL AND NUMERICAL INVESTIGATION OF LABYRINTH SEAL CLEARANCE IMPACT ON CENTRIFUGAL IMPELLER PERFORMANCE

Labyrinth seals are widely used in industrial multistage centrifugal compressors to reduce internal leakage and maintain compressor performance for a prolonged operation time. The leakage flow across the shroud seal of covered impellers and the hub seal of the rotating shaft has an important effect on the compressor performance. The amount of leakage flow is primarily a function of seal running clearances, which is typically designed based on the compressor working environment, such as pressure and temperature conditions. The present paper discusses the experimental and numerical studies of seal clearance impact on the performance and operation of a single stage centrifugal compressor. Two experimental campaigns of running a medium-flow coefficient impeller and a low-flow coefficient impeller with various radial clearances of the impeller shroud and the hub labyrinth seal were conducted based on the configuration of the impeller and the return channel system in a closed-loop compressor test rig. The experimental investigation consists of both the overall stage performance test and the traverse test of the flow field downstream of the impeller using three-hole Cobra probes. Static pressure taps were arranged in the impeller shroud cavity in order to obtain the stream-wise pressure distribution. CFD simulations were then performed to compare with the test results. The paper presents the analysis of test data and simulation results of five arrangements of the impeller shroud and the hub seal radial clearances. The impacts of seal clearance height on stage efficiency and head are quantitatively evaluated. The impact on impeller internal flow field and cavity pressure distributions and swirl angle are discussed. Findings from this study are that efficiency reduction with increased seal clearance was as expected, but impeller Euler work was significantly reduced. CFD simulation was validated as a tool for predicting these effects and provides some understanding of the flow mechanisms.