<p>The centrifugal compressor features a compact size and a high pressure ratio and thereby is widely used in various applications. As a matter of course, not only high pressure ratio but high efficiency are required as the performance of the compressor. In a centrifugal compressor with a vaned diffuser, the flow field is inherently unsteady due to the influence of interaction between the impeller and the diffuser, and the unsteadiness of the flow field can often have a great influence on the aerodynamic performance of the compressor. In that sense, many experimental and numerical studies have been conducted on such unsteady effect associated with blade row interaction. In general, low-load compressors are likely to have a small-scale flow fluctuation according to the magnitude of blade row interaction, so the unsteady effect is expected to be relatively less in such compressors. However, in high-load compressors with stronger flow unsteadiness, it is considered that a large unsteady effect is produced on the aerodynamic performance of compressor. The unsteady effect on aerodynamic performance of the compressor is still unknown, and steady-state RANS simulation finds it difficult to predict the compressor performance. One of the reasons for that difficulty is because the unsteady effect, which should be expressed by deterministic stress, is neglected in such steady-state simulation with the mixing plane approach.<br>
In this study, numerical simulations have been conducted for a transonic centrifugal compressor with a vaned diffuser to investigate the unsteady effects associated with blade row interaction between the impeller and diffuser on the internal flow and aerodynamic performance of the impeller. The unsteady effects were clarified by comparing the numerical results between a single-passage steady-state RANS analysis and a full-annulus unsteady RANS analysis. The comparison of simulation results showed the difference in entropy generation in the impeller. The impingement of diffuser shock wave with the impeller pressure surface brought about a cyclic increase in the blade loading near the impeller trailing edge. Accordingly, with increasing tip leakage flow rate, a second tip leakage vortex was newly generated in the aft part of the impeller, which resulted in additional unsteady loss generation inside the impeller.</p>

Unsteady Effects of Blade Row Interaction on Flow Field and Aerodynamic Performance of a Transonic Centrifugal Compressor Impeller

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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