Measurement of Flow Field Characteristics in a Supersonic Inlet by FBG Sensors

This article describes the implementation of fiber Bragg grating (FBG) strings to simultaneously measure pressure, temperature, and terminal shock in a supersonic inlet. For the demanding conditions of wind tunnel testing and the measuring needs of supersonic inlets, together with simulation and experimental research, an FBG-based device for measuring flow field characteristics in supersonic inlets has been developed. The device consists of a bare FBG string for measurement and a steel tube-encapsulated FBG string for temperature compensation. By sensing the changes in flow conditions at multiple points in real time, they are buried by the polymer in slots on the surface of the inlet to measure temperature and pressure variations. The experiments were performed in a wind tunnel at a Mach number of 2.0, and the findings revealed that the pressure data obtained using the FBG-based measuring method suggested in this work were quite similar to that obtained using traditional pressure sensors. The signal measured by FBG had good repeatability and the error was within the tolerance of the supersonic inlet pressure measurement. The position of the terminal shock can be achieved according to the measured pressure distribution. In addition, the temperature could be measured by comparing the signal of the FBG string encapsulated in steel tubes with the signal of the bare FBG string. It was shown that the measuring method was appropriate for supersonic ground-based aerodynamic tests.