Development of a nanoscale hot-wire probe for supersonic flow applications
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A new nanoscale thermal anemometry probe (NSTAP) was designed and fabricated to measure mass flux in supersonic flows. This sensor was evaluated in the Trisonic Wind Tunnel Munich (TWM) at both subsonic and supersonic speeds. Subsonic compressible flow tests were performed to confirm the new sensor’s repeatability and to compare its behaviour to measurements from a conventional cylindrical hot-wire, while supersonic tests were performed to investigate the nature of the convective heat transfer from the nanoscale sensor at those conditions. For the range of mass fluxes tested in the supersonic regime, a linear relationship between the Nusselt number and the Reynolds number fit the data well. A linear relationship has previously been noticed at length scales close to the molecular mean free path of the flow and has been attributed to the free-molecule flow regime, where the Knudsen number is on the order of unity.
This work was supported by the AFOSR FA9550-16-1-0170 (program manager: Ivett Leyva) and by the German Research Foundation (DFG). This work was also partly supported by the DFG Priority Programme SPP 1881 Turbulent Superstructures project number KA1808/21-1. The authors are grateful for having participated in the Sonderforschungsbereich Transregio 40 program as this initiated collaboration between both institutions. The authors particularly thank Dr. Christian Stemmer for his support throughout the program. The authors are also grateful to Princeton University’s clean room staff for their advice regarding certain manufacturing processes. In particular, the authors thank David S. Barth for his assistance using the scanning electron microscope. Finally, the authors thank Prof. Alexander J. Smits for his helpful discussions.
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