Characterization of a hot-film probe for hypersonic flow

The critical issucs conccrning the application of constant-temperatnre hot-film anemomctry to hypcrsonic flow are reviewed and extended. Mass-flux static calihrations were conducted in a Mach 10 helium flow, while mass-flux and total-temperature static calibrations were made in a Mach 6 air flow. In addition, comparative hot-film/hot-wire turbulencc measurements were made in a Mach 11 helium boundary layer to provide insight into the dynamic rcsponse of the hot film. Thc measurements indicate that substrate conduction "losses" dominate the static response of the hot-film probe, thus resulting in poor sensitivity to mass-flux and total temperature. Furthermore, it has been found that it is not possible to isolate mass-flux fluctuations at high overheat ratios for the current hotfilm design. Thus, the sapphire-subsbrate hot-film anemometer is a robust, high-bandwidth instrument limited to qualitative transition and turbulence measurements. Finally, the extension of this technique to providing quantitative information is dependcnt upon thc development of lower thermal-conductivity substratc materials. 4