Stall and recovery process of a transonic fan in presence of inlet distortion

With recent trends in the design of civil engines with shorter inlet ducts, or boundary layer ingesting engines, reliable modelling of fan/distortion interactions and prediction of the safe operating range is becoming increasingly important. The aim of the current research is to study the stall and recovery behavior of a transonic fan stage with and without inlet distortion. For this purpose, simulation of the stall and recovery process of NASA stage 67 is performed with clean and distorted inflow conditions. The rotor is pushed into stall by closing the exit nozzle. It is shown that in both cases, stall is initiated with a spike but the subsequent development of the stall differs. In the stable rotating stall both cases contain one stall cell travelling at 63% shaft speed. During the recovery process, when the exit nozzle is gradually opened, the size of this stall cell reduces as the mass flow increases. Although the fan stalls at a larger mass flow with inlet distortion, it recovers to a similar corrected mass flow as the clean inflow, which indicates that inlet distortion has minor effects on the recovery process for this blade.