Performance Variation of Transonic Centrifugal Compressor at Different Tip Clearances Using Numerical Simulations

One of the prime contributors to entropy generation and performance loss in centrifugal compressors is the presence of tip-clearance gap and associated tip-leakage flow. This paper aims to study the fundamental performance variation of a high-pressure transonic centrifugal compressor at different tip clearances using three-dimensional (3D) numerical simulations. In this study the test case used is the transonic SRV2-O compressor designed and developed by DLR (German Aerospace Center). Reynolds Averaged Navier-Stokes (RANS) based k-μ model has been used for numerical simulations. The performance of centrifugal compressor is significantly affected by tip-leakage flow, which combines with the secondary flow and results in a considerable entropy generation accumulated at the shroud suction-side of the impeller blade. For understanding of flow mechanism, eleven different tip clearances have been simulated along with comprehensive evaluation of the tip-leakage flow. At constant tip-clearance ranging 0.01 to 1mm, a loss of about 17.7% occurred in the stage pressure ratio of compressor and isentropic efficiency was dropped by 5.5%, at design conditions of 2.55 kg/s of mass flow rate and 50,000 1/min. The compressor isentropic efficiency and pressure ratio is observed optimum at constant tip-clearance in range 0.09 mm and 0.18 mm. While at variable tip-clearance between leading-edge (LE) and trailing-edge (TE), almost 11 percent loss has been noted in the stage pressure ratio, while isentropic efficiency was reduced by 3.3 percent as tip clearance increased from 0.3 to 1.1mm at the leading edge and 0.1 to 0.9 mm at the blade exit of the impeller. This paper provides the quantitative estimate of losses in compressor pressure ratio and efficiency due to tip-clearance.