Characteristics of Thermal Anemometers at Low-Pressure Condition in a Mars Wind Tunnel

In this study, we have investigated the sensitivity and the time response characteristics of thermal anemometers such as a hot wire in low-pressure environment. To achieve this purpose, we developed the calibration device to calibrate a thermal anemometer under lowpressure condition. By using this device, we investigated the relationship between Reynolds number and Nusselt number at 1 kPa to 80 kPa and Mach number 0.1 to 0.95, for a standard hot-wire having a diameter of 5 µm. We found that the sensitivity of the hot-wire anemometer reduces with decreasing pressure and the time response characteristics get drastically worsen. However, the results of calibration with higher overheat ratios show that the sensitivity and the time response can be improved by increasing wire temperature, particularly in low-pressure condition. These results would provide guidelines for measuring turbulent intensity in a low-density wind tunnel such as a Mars wind tunnel to simulate the flight environment of a Mars airplane.