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Aerodynamic performance prediction models for centrifugal compressor impellers are presented. In combination with similar procedures for stationary components, previously published in the open literature, a comprehensive mean streamline performance analysis for centrifugal compressor stages is provided. The accuracy and versatility of the overall analysis is demonstrated for several centrifugal compressor stages of various types, including comparison with intrastage component performance data. Detailed validation of the analysis against experimental data has been accomplished for over a hundred stages, including stage flow coefficients from 0.009 to 0.15 and pressure ratios up to about 3.5. Its application to turbocharger stages includes pressure ratios up to 4.2, but with test uncertainty much greater than for the data used in the detailed validation studies. IntroductionMean streamline aerodynamic performance analysis continues to play a key roll in the design and application of centrifugal compressors. Despite impressive progress in computational fluid dynamics procedures, mean streamline methods continue to be the most accurate and the most practical method of predicting the performance of a stage or a component of a stage. Whitfield and Baines (1990) and Cumpsty (1989) contain good recent overviews of mean streamline methods. The analysis described here has been under development for over twenty years. Literally hundreds of different stages have been analyzed with it.Detailed comparison of experimental data with predicted results has been accomplished for over a hundred stages. However, the best test of a performance analysis is its application to design activity. Weaknesses in the analysis are most clearly exposed when designers use it to guide them to better performing stages or components. This analysis has been revised and requalified each time sufficient test results from stage development programs were available to define significant deficiencies. The seventh major revision of the analysis is now in use. It has been successfully supporting stage development activity for over four years. It is applied to a variety of stage types, including process compressors, air compressors, and turbochargers. The detailed validation studies include stage flow coefficients, cj>, from 0.009 to 0.15 and pressure ratios up to about 3.5. Good results have also been obtained on applications to turbocharger stages for pressure ratios up to about 3.5. Good results have also been obtained on applications to turbocharger stages for pressure ratios up to 4.2. However, test uncertainty for these units is much greater than for data used in the detailed validation studies.Methods used in this analysis to predict performance for stationary components have previously been published in the open literature. These include prediction methods for vaned diffusers (Aungier, 1990), vaneless diffusers and return systems (Aungier, 1993), and volutes (Weber and Koronowski, 1986). The present paper provides a description of the impeller perform...

A modified form of the Redlich-Kwong two-parameter equation of state is presented. The modified equation employs the acentric factor and the critical point compressibility factor as additional parameters to improve its accuracy and to extend its application range to include the critical point. This modified equation is as simple as the original form, yet achieves substantially better prediction accuracy, including thermodynamic parameters such as enthalpy and entropy. Results from this equation, the original equation, and three other popular modified forms are compared with gas property data for several compounds to demonstrate its improved accuracy and increased application range. Practical application limits to the other modified forms are identified to guide current users of those methods.

The performance of centrifugal compressors can be seriously affected by inlet flow distortions due to the unsatisfactory nature of the inlet configuration and the resulting inlet flow structure. Experimental tests have been carried out for the comparison of centrifugal compressor stage efficiency with two different inlet configurations, one of which is straight with constant cross-sectional area and the other a 90° curved pipe with nozzle shape. The comparative test results indicated significant compressor stage performance difference between the two different inlet configurations and the details are discussed to understand the performance behaviour of the compressor exposed to the distorted flow from the bend inlet configuration. The experimental investigation motivated the need for a new inlet design as well as a clear picture of the detailed flow field in the existing inlet design using numerical simulations. Two design approaches are reported in this paper, one of which is the location of vanes and the other the length of the curvature radius. For a more effective design method, a generalized formula is developed for the optimum position and number of vanes in such a way that each divided flow passage with vanes shares the same pressure gradient in radial direction. Numerical simulation results are presented and discussed in terms of mass-averaged parameters and flow structures, based on the comparison of flow properties at the pipe exit cross-sectional area of each design. Finally, new designs of different inlet systems are proposed to reduce the secondary flow and to provide flow as uniform as possible for a compressor.