An Active Flow Distortion Control System for Serpentine Inlets

An active flow control system for reducing distortion in serpentine inlets was developed using non-intrusive microphones as feedback sensors. While the serpentine inlet can provide large benefits to an air vehicle by reducing its overall size and therefore weight, it unfortunately delivers a non-uniform (spatially-distorted) flow to the compressor due to the formation of a secondary flow created by separation of the turbulent boundary layer in the aggressive turn. An active means of controlling distortion has been developed using an array of micro air jet vortex generators. It was hypothesized that microphones in the vicinity of the distorted flow would record higher amplitudes pressure fluctuations compared to those microphones in the vicinity of the undistorted flow. Experiments showed that the difference between the microphone readings in these two flow regimes was correlated to the distortion level. This difference in microphone signals was then used as feedback in a PID control system that regulated spatial distortion levels during steady flight conditions, as well as sudden ramps in aircraft speed.