Centrifugal compressors employed in the oil and gas industry are operated at high gas pressure conditions and are used in a wide operation range. Accurate prediction of the rotating stall and the destabilizing aerodynamic force is one of the key technologies for these compressors, because rotating stall can sometimes cause severe problems with subsynchronous shaft vibration and limit its operation range. Thus, the aim of this study is to establish a method of accurately predicting the inception of rotating stall and its effect on shaft vibration. To achieve this, numerical investigations are carried out by unsteady Reynolds-averaged Navier-Stokes (RANS) simulation with a full annulus model of the compressor stage. Also, to assess the accuracy of the simulation qualitatively and quantitatively, a high-pressure compressor test rig that contains a shrouded impeller and a vaneless diffuser is built. To investigate the effect of the rotating stall on the shaft vibration, an experiment is carried out at relatively high gas pressure with the inlet pressure level exceeding 30 barA.
In the first part of the study, the accuracy of compressor performance prediction is studied by steady computational fluid dynamics (CFD) simulation. It is found that by taking the wall roughness effect into account, the predicted performance shows good agreement with the experimental result. Thus, a subsequent study of the rotating stall is also carried out by considering its effect.
In the second part of the study, the accuracy of predicting the rotating stall is studied. In the experiment, two types of rotating stall are measured. One is a multiple-cell stall induced in the vaneless diffuser, for which the speed of rotation is relatively low and the other is a one-cell stall induced in the impeller region. The properties of the multiple-cell stall agree with the previous experimental and numerical studies, and the rotating stall has the limited effect on shaft vibration. Conversely, the one-cell stall shows severe subsynchronous vibration. In this study, both types of stall prediction are examined by CFD simulation. It is found that the simulation can predict the inception of the rotating stall with relatively high accuracy as the predicted results show good agreement with the experimental results in terms of cell count, rotation speed, pressure fluctuation level and the effect on shaft vibration. Through this study, the effectiveness of unsteady CFD simulation is confirmed for these types of stall and vibration prediction.