Calibration Methods for a Constant Voltage Anemometer-Operated Hot-Wire in a Hypersonic Flow

Abstract

The calibration of measurements made with a CVA-operated hot-wire, in a quiet hypersonic wind tunnel, are examined. Two calibration methods are evaluated. The first calibration method is based on the ratio of the power dissipated in the hot-wire and the difference between the hot- and cold-wire resistances. The second method is based on the traditional semi-empirical heat transfer relation for a heated wire in supersonic/hypersonic flow. The mean mass flux and total temperature derived from the calibration methods show overall good agreement with Navier-Stokes predictions. In general, the first method gives better results across the boundary layer. However, limitations in the calibration data meant no definitive assessment of the capability to yield fluctuation measurements could be made. The recently derived sensitivity coefficients for a CVA-operated hot-wire are used to obtain fluctuation measurements. Also, the fluctuating diagram method is used to evaluate the performance of the NASA Langley Mach 6 quiet tunnel and to detail the characteristics of the fluctuations in the laminar hypersonic boundary layer. Within the boundary layer, profiles of the measured rms fluctuations and the fluctuation diagrams show that the intensityof the boundary layer disturbance fluctuations are most intense in the vicinity of the critical layer. The static pressure fluctuations derived from the fluctuation diagrams verify that the fluctuations are less than 0.2%. This observation confirms previous qualitative observations of the performance of the Mach 6 quiet nozzle.