The Cost of Flow Control in a Compressor

This paper documents an analysis performed to estimate the cycle cost of flow control in a compressor. The analysis is based on a series of experiments conducted in a low-speed compressor cascade at high incidence. In these experiments, flow control was applied to delay a turbulent separation on the suction surfaces of the blades in the cascade. The flow control methods studied include boundary layer suction and both steady and pulsed vortex generator jets. Endwall control was also applied to remove corner separations. Tip gaps and endwall suction were both studied for this purpose. The flow control methods studied were able to successfully delay a separation occurring on the suction surface of the blades, reducing the loss coefficient. The mass flow rates and jet supply pressures required to achieve control in each case were used to model a single flow-controlled blade row in a typical turbofan cycle using cycle analysis software. The cost of control to the cycle was calculated as the polytropic compressor efficiency increase required to maintain thrust relative to a conventional cycle with no flow control. The results of the analysis show that the benefits of flow control significantly outweigh the cost. They also show that boundary layer suction coupled with endwall suction yields the lowest cycle cost. This is because of the small pressure difference required to drive suction, which allows reinjection of the aspirated air a short distance upstream of the flow controlled blade row.