Effect of Nozzle Injection on Controlling Surging in Centrifugal Compressor (Influence of Injection Nozzle Structure)

Centrifugal compressor, which is the main component of turbocharger, is known to suffer the instability phenomena such as surge at low flow rate conditions. The nozzle injection system is an effective method to suppress the instability phenomena. In the system, a part of the air compressed by the compressor is bled from the scroll outlet and injected into the impeller inlet by the nozzle installed on the inner wall of suction pipe. The conventional type of injection nozzle is composed of the circular pipe which may locally obstacle the main flow in the suction pipe. In this study, the wall jet type of injection nozzle whose discharge port was located on the inner wall surface of suction pipe was investigated to reveal its effectiveness on the surge suppression. The present results indicate the importance of the injection to the tip of leading edge and the axial momentum of jet.