Axial Compressor Design with Counter-Rotation and Variable RPM for Stall Mitigation

Compressor Stall, an aerodynamic instability due to abnormal air flow in the compressor resulting in loss of total pressure and compressor performance. One of the reasons of compressor stall is due to rise in static back pressure at compressor exit which may result from an imbalance of incidence angle at the rotor and stator and rotational speed. The paper presents the results of a new axial compressor design with counter rotation and variable RPM. Counter-Rotation is used to push compressor performance during stall by moving the operating point away from surge line with a higher pressure ratio rise. Initially an axial compressor is designed with counter-rotation at design point. The flow is modelled by means of Navier-Stokes computation using the upstream rotor conditions and exit static pressure condition with k-epsilon as the turbulence model. Compressor exit conditions are then changed to stall the compressor. After the compressor stalls the RPM of the counter-rotating stage is varied until the compressor recovers from the stall. This novel idea unlike the conventional stall control systems mitigates the stall without compromising compressor performance, in fact it helps to increase the performance and pressure ratio of the compressor with the means of counter-rotation and variable RPM