Measurement of Buzz Flows in a Supersonic Inlet by FBG Sensors

This article presents a new approach that utilizes fiber Bragg grating (FBG) pressure sensors to detect subcritical conditions and buzz flows in a supersonic inlet. Based on the measurement requirements of supersonic inlet flow fields and the testing specifications for wind tunnel tests, a diaphragm-based FBG pressure sensor model that comprises a protective gel, a fixed ring, an FBG sensor, and a sensing diaphragm is designed. In addition, small deformation theory and finite-element simulation were used in the sensing material selection and sensor dimension optimization, resulting in a pressure sensitivity for the sensor of 30.97 kPa/nm as determined through calibration. Experimental validation in a supersonic wind tunnel confirmed the FBG sensors' accuracy in measuring inlet flow characteristics. Comparative analysis against conventional sensors demonstrates the FBG sensors' proficiency in capturing both instantaneous pressure fluctuations and steady-state values with less than 5% error. As the throttling ratio (TR) increases, FBG sensors successfully identified the emergence and evolution of subcritical conditions and buzz flows, with signal frequencies postoccurrence of the buzz flows concentrated at 142 and 147 Hz, thereby unveiling the instability in the flow field. This study highlights the potential of FBG-based systems for detecting buzz flows in supersonic inlets, indicating significant advancements in aerodynamic testing for airbreathing propulsion systems.