Influence of Cavity Flows Modeling on Centrifugal Compressor Stages Performance Prediction Across Different Flow Coefficient Impellers

Abstract

Computational Fluid Dynamics (CFD) is becoming fundamental to predict turbomachinery performance. However, only using advanced numerical models coupled with high fidelity grid generation is possible to reach a very good matching with test data. In this regard, secondary flow modeling plays a critical role in the accuracy of performance prediction for centrifugal compressor stages. This study analyses the effects of cavity models on centrifugal compressor stages performance across the full range of impeller flow coefficients used in common industrial applications. Both bi-dimensional low flow coefficients with splitter and non splitter blades and three-dimensional high flow coefficients stages have been used as test cases to compare the numerical prediction with test data. Furthermore the effects of secondary flows modeling have been assessed when comparing detailed flow features with advanced experimental data both in terms of 1D profiles and 2D maps. The effects of cavity flows modeling is growing, as expected, moving to very low flow coefficients, reaching several points of difference in efficiency calculation with respect to simpler models. Furthermore, the agreement with experimental data is very good both in terms of overall performance and detailed flow features. Finally, the high fidelity CFD is capable to give deep in-sides into the flow evolution inside the machine allowing aero designers to design centrifugal compressor stages with higher performance. It should be remarked here that a good matching of CFD prediction with test data is possible only by using high fidelity models.