Cavity Flow Modeling in an Industrial Centrifugal Compressor Stage at Design and Off-Design Conditions

Numerical tools and test equipments used in the design and validation of modern centrifugal compressor stages need to be at the state-of-the-art. In particular, a big effort is currently made to correctly model secondary flows that play a relevant role in the accuracy of the performance prediction. This paper presents the flow analysis of a high efficiency centrifugal compressor stage using high accurate computational fluid dynamics with a particular attention to the cavity flows modeling. Experimental data were also available and used to validate the numerical results. The key experimental data coming from an advanced FRAPP (Fast Response Aerodynamic Pressure Probe) and traditional probes are presented in the study as overall performance and flow features details. Test data are in fact necessary to validate and continuously improve the numerical techniques. The geometry of the stage including full modeling of the secondary flows cavities were faithfully reproduced in the computational model. The availability of new in-house automated tools for cavity meshing allow compressor aero-designers to accurately resolve leakage flows with a reasonable increase in computational and user time. The results of the computational model were in excellent agreement with the experimental data both in terms of overall performance and main flow field structures. Also details of the flow features inside the cavities matched the test data very well. Only using high accurate geometry modeling including leakage flows was possible to capture important flow features that instead were not correctly simulated with simplified computational models.