CORE-COMPRESSOR ROTATING STALL SIMULATION WITH A MULTI-BLADEROW MODEL

The paper will focus on one specific core-compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The long-term aim is to minimize the forced response due to rotating stall excita- tion by avoiding potential matches between the vibration modes and the rotat- ing stall pattern characteristics. Using a 3D viscous time-accurate flow repre- sentation, the front bladerows of a core-compressor were modeled in a whole- annulus fashion. The engine core flow boundary conditions were obtained from a mixing-plane steady-state calculation for which the low pressure compression domain was also modeled. A variable-area nozzle, placed after the last com- pressor bladerow in the model, was used to impose ambient boundary conditions downstream. The rotating stall behavior at two different compressor operating points was studied by considering two different variable-vane scheduling condi- tions for which experimental data were available. In all cases, the rotating stall was initiated by introducing a small amount of geometric mistuning to the rotor blades. Using 3- and 6-bladerow models, the unsteady flow calculations were conducted on 32-CPUs of a parallel cluster, typical run times being around 3-4 weeks for a grid with about 30 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, 6 rotating stall cells were obtained for the first scheduling condition while mal- scheduling of the stator vanes increased the number of rotating stall cells to 13. Although there was some discrepancy between predicted and measured speed of the rotating stall pattern, it was concluded that the large-scale modeling method- ology could simulate both the onset of rotating stall and its development as a function of vane scheduling.