Computational studies of unsteady flows in a centrifugal compressor stage

This paper describes the flow analysis in a centrifugal compressor stage using a three-dimensional computational fluid dynamics (CFD) algorithm. The flow unsteadiness arising from the interaction between the impeller and the diffuser has also been analysed using an algorithm suitable for equal or multiple numbers of rotor and diffuser blades. The multi-block, structured grid CFD code TASCflow which provides an approximate solution to the Reynolds-averaged Navier-Stokes equations was used as a basis and algorithm development was undertaken to provide the required capability of modelling the unsteady interactions of the impeller and the diffuser. The centrifugal compressor stage under investigation consists of 28 radial blades (of which 14 are splitter blades) in the impeller and 27 vanes in the diffuser. The presented results and analysis are for off-design flow conditions where experimental results were available for comparison. The results obtained for the steady-state model show a reasonable agreement with the measurements. In general the unsteady flow field obtained shows a reasonable agreement with experimental data and exhibits considerable differences when compared with the steady-state results.