High Temperature Static and Dynamic Pressure Transducer for Combustion Instability Control Using Acoustic Low-Pass Filter Structures

Abstract

There is a need to measure static and dynamic conditions in many gas turbine applications, in particular for combustion instabilities, such as those in the afterburner. The DC and low frequency components are typically used for conventional engine control, while the high frequency data is essential for acoustic screech and rumble diagnostics and control. This paper presents a static-dynamic piezoresistive pressure transducer that measures low amplitude, dynamic pressure perturbations superimposed on top of a high pressure through the implementation of low pass mechanical structures. The transducer, which is capable of operating at ultra-high temperatures and in harsh environments, consists of a static piezoresistive pressure transducer, which measures the large pressures on the order of 200psi and greater, and an ultrasensitive, dynamic piezoresistive pressure transducer which captures small, high frequency pressure oscillations on the order of a few psi. The heightened sensitivity in high pressure environments is achieved by filtering the measured pressure of high frequency content through an innovative low pass mechanical filter structure. The large static pressures passed by the low-pass mechanical filter structures are routed to the backside of the dynamic pressure sensor, which results in both the front and the back of the dynamic sensor being exposed to the large pressures within the environment. Therefore, the large static pressures cancel out, and the dynamic sensor only senses the low magnitude, high frequency pressure perturbations. This dual sensor, static-dynamic pressure transducer reproduces pressure signals with sensitivity far higher than any single high pressure transducer available today. The dual sensor, static-dynamic transducer meets the pressure sensing specification of numerous applications including, but not limited to, the following: the optimization of turbine operation, turbine design and testing, the detection of the onset of rotating stall and surge in turbine compressors, and combustion instabilities. This paper describes a six element model of the static-dynamic transducer’s low-pass mechanical filtering structures. The paradigm is derived from first-principles of fluid motion in acoustic ducts with viscous dissipation. A dynamic pressure source is used to verify the model and its operation. Finally, a transfer function characterization of a fully operational static-dynamic pressure transducer over a wide bandwidth is presented. Based upon the analytical and experimental results, the static-dynamic pressure transducer will make it possible for turbine users and manufacturers to implement ultra-sensitive pressure monitoring to reduce compressor and combustion instabilities [1] [2].