High-Temperature Screech and Acoustic Sensor for Turbine Engine Augmentor

In order to increase thermodynamic efficiency, high performance military gas turbine engines are being operated at lean fuel-to-air mixtures which approach the limits of combustion. Within this lean mixture regime, the engine is prone to thermoacousticinstabilities, which may cause unstable operation, and even lead to flameout in extreme cases. This phenomenon can be extreme in engine augmentors, where resonances known as screech and rumble may generate peak-to-peak pressures up 20 psi at frequenciesranging from 50 to 600 Hz. Rumble and screech are undesirable because they may lead to fatigue of engine components, they reduce operating efficiency of engine, and they may unstart the engine by flameout.Prime Research, LC, in collaboration with the Virginia Tech Center for Photonics Technology, proposes to design, develop, and demonstrate a dynamic pressure sensor for in-service monitoring of pressure fluctuations that accompany the onset of rumble andscreech in turbine engine augmentors. The proposed pressure sensors will be based on sapphire optical fiber technology so that they can withstand the high temperatures of the augmentor. The sensors will demonstrate frequency response of better than 3,000Hz, resolution of 0.15 psi or better, and accuracy of 5% full scale. Application of active control systems to stabilize thermoacoustic instabilities in turbine engine augmentors will require development of robust sensors, actuators (flow controllers), and control algorithms. The proposed program develop flight-weightdynamic pressure sensors that can withstand the high temperatures in the proximity of the augmentor liner, so that the sensors may be close-coupled to the augmentor cavity in order to achieve fast response times. A pressure sensor based on opticalinterrogation of a diaphragm made from a high-temperature material is proposed, due to the many advantages of optical sensors for harsh environments.