19/02/2020 – K. Kokmanian – Development of nanoscale hot-wire probes for supersonic flow application

Séminaire exceptionnel IUSTI – 19 fév. 2020 – 11h salle 250

Development of nanoscale hot-wire probes for supersonic flow application

Katherine Kokmanian – MAE, Princeton Univ, ÉU

Due to their wide range of length and time scales, three-dimensionality and high diffusivities, turbulent flows remain poorly understood and extremely challenging to accurately characterize. In order to fully capture the flow dynamics, highly resolved instrumentation is needed. With the advancement of semiconductor manufacturing, the nanoscale thermal anemometry probe (NSTAP) was designed to acquire well-resolved data in a variety of incompressible turbulent flows. These miniature silicon-based devices have been shown to decrease spatial filtering and increase temporal resolution, which makes them attractive to use in supersonic flows. However, due to the increased structural loading and added mathematical complexities correlated with compressible flows, the NSTAP must be redesigned and well-characterized in these high-speed flows prior to its extensive use. It has been previously found that, when dealing with conventional cylindrical hot-wires, the Nusselt number dependence on Reynolds number shifts from a square root to a linear relationship as the Knudsen number increases. This transition occurs when reaching the free-molecule flow regime and has been studied both theoretically and experimentally. Due to the small length scales of the NSTAP, and hence the high Knudsen numbers experienced by the sensor in supersonic flows, it is believed that this linear calibration regime can be reached, which would significantly simplify both data acquisition and data processing. Here, we report the necessary design changes of the NSTAP to function in supersonic flows. We also report data taken in the freestream of a Mach 2 flow where the heat transfer characteristics of these miniature hot-wires are investigated. The data was collected over a range of flow conditions in the Trisonic Wind Tunnel Munich (TWM) in collaboration with Prof. Kähler’s research group at Bundeswehr University Munich.