Fiber-Optic Hot-Wire/Hot-Film Anemometers for Turbulence Measurement

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Non Technical Description:The study and control of turbulence are critical for the development of next generation jet engines, combustion chambers, and power plants with maximum performance and efficiency, which are expected to operate in increasingly harsh environment involving high temperature, high corrosivity, and large electromagnetic interference. Hot-wire/hot-film anemometry that can accurately capture and characterize the flow parameters is crucial for the fundamental understanding of turbulence. Traditional hot-wire anemometers often cannot survive or have significantly reduced performance under these environments. Fiber-optic hot-wire/hot-film anemometry is an emerging technology that has the potential to perform in these environments because of their dielectric structure and optical operation. Current fiber-optic hot-wire/hot-film anemometers, however, cannot meet the speed, sensitivity, and spatial resolution required for the study of turbulent flow. The research proposed in this application is aimed at drastically improving the performance of fiber-optic hot-wire/hot-film anemometers and make them a viable solution for turbulence measurement in harsh environment. The project will also provide research and education opportunities to graduate and undergraduate students in the field of optics. K-12 school students and teachers will be involved in the project through several existing outreach programs. Technical Description:The project will investigate new heating and temperature sensing mechanisms on ultra-thin silica wires and silicon films as well as novel sensor demodulation methods that can drastically improve the speed, sensitivity, and spatial resolution of the device. The project consists of five research objectives: 1) Investigate new mechanism to minimize the "end-conduction" effect for improved anemometer response to high-frequency flow components. 2) Develop novel epoxy-free fabrication methods for sensor operation under harsh environment. 3) Study novel mechanisms to increase the quality factor of the optical resonators for improved anemometer performance. 4) Further increase the sensor speed through a new constant-temperature operation mode that can automatically compensate for the thermal inertia of the sensing element. 5) Characterize and test the fiber-optic anemometers in room-temperature and high-temperature environments. The proposed research will advance the field of turbulence study by enabling the new applications of hot-wire/hot-film anemometry in harsh environments. Miniaturized fiber-optic hot-wires/films also allow to characterize liquid/gas flows in remote and/or difficult-to-access sites with applications in much broader communities such as biology, health care, chemical engineering, and oceanography.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.