Rotating Stall in Axial Flow Compressors

Ever increasing demand of higher pressure ratio of aero-engine compressors has always been hindered by two distinct aerodynamic instabilities. The first known as surge is; large one dimensional periodic mass flow fluctuation through the compressor, which involves the entire pumping system including compressor, ducting, plenum and throttle. The second is the rotating stall which can be characterized by a wave travelling about the circumference of the machine. It is local to the blade rows of the compressor and can lead to the surge. Both these instabilities can reduce the pressure rise in the compressor, cause over-heating of the blades and can result in severe mechanical damage to the machine. The researchers have been trying to fully resolve these complex phenomena but many aspects are still unsolved problems. In the case of rotating stall, the efforts to predict its inception and analyse the flow during and after its occurrence have met with limited success. Some passive techniques such as rotor casing treatment and employment of flow distortion control screen are already in use to delay the rotating stall. Recently, successful laboratory experiments have been conducted regarding the active suppression and control of the stall and for the bifurcation analysis of the stall and surge in axial compressors.