Using Unsteady Analysis to Improve the Steady State Computational Fluid Dynamics Assessment of Minimum Flow in a Radial Compressor Stage

Abstract

This paper presents a computational fluid dynamics (CFD) study performed to assess the prediction of the minimum stable volume flow for a high Mach number, high head, and high volume flow compressor stage. CFD was run on a “pie slice” or sector stage model in steady-state condition and on a full 360 deg stage model under both steady and unsteady state conditions. The predictions of the minimum stable flow were compared to experimental data. Results showed the CFD performed on the “pie slice” stage model over-predicted the minimum stable flow by 9% compared to the test results, while the transient CFD predicted the minimum stable flow within 5.8%. Flow field comparisons of the impeller between unsteady and steady state CFD revealed that the steady state CFD accurately predicted the flow phenomena until the onset of surge. However, the unsteady flow features could not propagate through the diffuser because of the limitations of the impeller-diffuser interface modeling in the steady state analysis.