In a compressor used for power generation, a rotating stall due to an operating point mismatch between the front and rear stages occurs at front stages in low-speed condition during startup. IGV, VSV opening schedule and bleed flow rates are determined in order to obtain stable operating conditions, with the occurrence of pressure fluctuations or blade excitation force derived from the rotating stall.
The setting of the number of stages for variable stator vane, the vane opening and the bleed flow rate are largely based on the rig test and experience of the actual machine, however we focused on the capability study for direct simulation with unsteady CFD for the rotating stall. If this can be predicted in advance, it makes it possible to reduce the number of stages of the variable stator vanes, the capacity of the thyristor, and to make the bleed chambers and piping compact, leading to cost reductions.
The method of rotating stall prediction during startup condition, and the comparison between predicted and actual measurements on how this number changes with different starting conditions and different machines, are shown in this paper. CFD shows the different stall cell position, the number of stall cells and the pressure fluctuation level in each condition, and these results were consistent with the measurement data. Furthermore, we have found that these phenomena can be controlled by variable stator vane angle during start up.