Compressible Flow Measurements Using Nano-scale Thermal Anemometry Probes

Nano-scale thermal anemometry probes (NSTAP) were used to extract spatially and temporally resolved mass flux measurements in compressible flows, where short time scales and high speeds are ever-present constraints. These miniature hot-wires (wires typically 100 nm thick, 2 μm wide and 60 μm long) were redesigned and mounted in the Trisonic Wind Tunnel Munich (TWM) located at Bundeswehr University and data was collected for a range of Reynolds and Mach numbers (5E6<Re<5E7 m^-1 and 0.3<M<2.0). Free-stream measurements were performed and the turbulence intensity was compared to that found using particle image velocimetry (PIV). Additional caution must be taken when calibrating hot-wires in supersonic flows as they are susceptible to total temperature changes as well as mass flux changes. Different calibration techniques were investigated and a linear relationship between the Nusselt number and the Reynolds number fit the NSTAP data best, which has previously been attributed to the free-molecular flow regime. We report recent efforts to validate this observation as well as to compare NSTAP and PIV data in the free-stream of the TWM at various flow conditions.