Unsteady Flow and Aeroelasticity Behaviour of Aero-Engine Core Compressors During Rotating Stall and Surge

The paper will focus on two core-compressor instabilities, namely rotating stall and surge. Using a 3D viscous time-accurate flow representation, the front bladerows of a core-compressor were modelled in a whole-annulus fashion whereas the rest of bladerows were represented in single passage fashion. The rotating stall behaviour at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with 9 whole bladerows, 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 60 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while mal-scheduling of the stator vanes created a 12 band rotating stall which excited the rotor blade 1^st flap mode. In a separate set of calculations, the surge behaviour was modelled using a time-accurate single-passage representation of the core compressor. It was possible to predict not only flow reversal into the low pressure compression domain, but also the expected hysteresis pattern of the surge loop in terms of its mass flow vs pressure characteristic.