Hot Wire Anemometry in Cold Mach 4 Flow

The Naval Postgraduate School operates a cold-flow Mach 4 supersonic wind tunnel, which was renovated in 2022 to improve test section flow conditioning. Post-modification, flow re-characterization focused on acoustic and turbulence intensity metrics. A Dantec constant temperature anemometer probe was used to assess freestream turbulence of the supersonic wind tunnel by laterally traversing the probe to locations of known Mach numbers. Surveys were conducted at 170 kHz and 1 MHz. Although calibration via the boundary layer profile was attempted, velocity conversion was hindered by an advection gradient between the freestream and boundary layer. Consequently, bridge voltage fluctuations were used to estimate pseudo freestream turbulence intensity—approximately 0.7% at 170 kHz and 0.5% at 1 MHz. Frequency spectrum analysis of the 1 MHz data revealed a 100 Hz flow structure in the freestream, absent from the boundary layer. While traditional turbulence intensity values were not acquired, the study yields a practical methodology for applying hot-wire anemometry in cold, constant-Mach supersonic wind tunnels.