Investigation of turbulence models for aerodynamic analysis of a high-pressure-ratio centrifugal compressor

Abstract

The aerodynamic design and optimization of modern centrifugal compressors are inseparable from computational fluid dynamics (CFD) tools. In a design environment, CFD simulations are expected to predict compressor performance characteristics with reasonable accuracy. Turbulence models and model simplification can play a significant role in the discrepancy between analysis and reality. To investigate the influence of turbulence models on aerodynamic analysis results of centrifugal compressors, the National Aeronautics and Space Administration's high efficiency centrifugal compressor stage is selected as the test vehicle. Six eddy-viscosity models, namely, Spalart–Allmaras (SA), standard k–epsilon (k−ε), renormalization group k–epsilon (RNG k−ε), Wilcox k–omega (k−ω), shear stress transport (SST), and SST-reattachment modification (SST-RM) are considered. In all numerical analyses, measured surface roughness is included with the aim of improving numerical solution accuracy. Although some discrepancies exist, the compressor performance characteristics predicted by the k−ω model are in satisfactory agreement with the test data over the whole speedline. The k−ε model overpredicts the isentropic efficiency than the other models, while the SST-RM model underestimates the total pressure ratio in the near-stall region. The RNG k−ε model matches high flow characteristics but overestimates the choked mass flow rate. The SST model obtains a similar operating range with the test data but underestimates the compressor's isentropic efficiency and total pressure ratio, while the SA model totally overestimates the compressor characteristics due to the wall function. Furthermore, variations caused by turbulence models are discussed together with the flow field analysis. Finally, to verify the impact of the impeller backplate bleed cavity, an additional simulation is conducted that specifically accounts for this feature.