URANS Simulation of Self-Recirculation Casing Treatment in a Transonic Compressor

Time-accurate numerical calculations are performed to investigate the effect of air recirculation on NASA Rotor 37. An annular casing-mounted recirculation passageway is designed and located over the blades. Because the investigated rotor does not have any stator, the bleed air has a high circumferential velocity component (in the same direction of the rotor). Therefore, the injected air would have a high swirl component, reducing the injection's effectiveness. As a result, anti-swirl blades have been installed within the recirculation duct, to reduce flow swirl and improve injector effectiveness. Different anti-swirl vanes have been simulated in order to determine the best vanes in terms of minimum pressure loss and zero injection yaw angle (axial injection). Results show that these vanes can effectively turn the circulated fluid to the axial direction and provide a high velocity axial injection upstream of the rotor blades. As a result of the effective injection, the leakage flow moves downstream, improving stability by shifting the stalling point to lower mass flow rates. Because the injection port is close to the blade, the interaction of the passage shock and the injection port causes unsteadiness in the injection mass flow, which is discussed in the paper.