The measured performance of a small turbocharger compressor has been analysed in order to develop a method of calculating the internal aerodynamic performance where only the basic compressor characteristic and geometry is available. Through the application of impeller and diffuser efficiency boundaries, the compressor internal component performance, such as impeller discharge angle and impeller relative velocity ratio, can be calculated within a small range of possible magnitudes. Impeller efficiency set equal to the square root of the stage efficiency offers a good approximation where impeller discharge static pressure measurements are not available. A procedure is devised so that the full compressor characteristic can be predicted using the known basic performance at one impeller speed, using either a fan law approach to predict the stage characteristic, or correlations for stage efficiency and an impeller slip factor. Where a vaned diffuser is used, it is found that correlation should be made against impeller discharge conditions, while in the case of a vaneless diffuser an average of impeller inlet and discharge conditions is found to be more suitable. The accuracy of the prediction procedures is shown to be satisfactory, however the ability to predict the onset of surge has not been addressed.

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