The flow instability always varies within different compressors; however, even in one compressor, there may be still multiple various unsteady modes. To study the triggering mechanism for these unsteady modes, a detailed experimental research on an industrial centrifugal compressor with variable vaned diffuser is performed from design point to surge. The multiposition dynamic pressure measurement is conducted during the whole valve-adjusting process. The characteristics of pressure fields under some specific operating conditions are focused on, especially the prestall, stall and surge conditions. According to the collected data, the features of different unsteady modes can be obtained, such as the surge pattern and the propagation direction of stall cells. In addition, when the diffuser vane setting angle (DVA) is adjusted, the core factors to trigger total instability will change. To better complement the experimental analysis, a multipassage numerical simulation is carried out. Based on the agreement of performance curves obtained by the two methods, the flow field characteristics in the prestall state shown in the simulation results are indeed a good complement to the dynamic experimental analysis. Meanwhile, with the help of dynamic mode decomposition (DMD) method, a few low-frequency unsteady structures are extracted from the transient numerical result over a long time, which correlate with the experimental result. Through detailed analysis, an insight into the different unsteady modes in a centrifugal compressor with variable vaned diffuser is obtained.
Modelling of surge phenomena in a centrifugal compressor: experimental analysis for control
