Progress in hot-film anemometry for hypersonic flow

A robust microsensor hot-film probe has been developed to obtain continuous turbulence measurements in moderately severe hypersonic environments. This probe represents a significant advancement of an existing concept. Optimization for hypersonic flow is achieved through sensor placement, the use of high-temperature materials, and state-of-the-art microphotolithographic fabrication techniques. Tests in Mach 6 air and Mach 11 helium flows have been very promising. The probe has exhibited excellent characteristics, including a frequency response that is a factor of 5 higher than that of previous hot-film sensors. The qualitative spectra of the anemometer fluctuations has been smooth and repeatable. Despite these improvements, heat conduction into the substrate still complicates the probe response. A review of the physics of this problem is presented along with a plan for the characterization of the response via several dynamic calibration techniques.