Apparatus for calibration of fine-wire sensors at stratospheric conditions

Abstract

A small-scale, open-circuit wind tunnel was developed to calibrate balloon-born fine-wire anemometers for conditions in the stratosphere. The system enables calibration of hotwire anemometers to test gases at flow velocities between 1 and 5 m/s and pressures between 550 and 5475 Pa. Using a metered inflow of test gas into a long circular cross-section pipe, a parabolic velocity profile is expected at the measurement plane for the fully-developed flow as described by Poiseuille flow theory. Traversal of a commercially available hotwire anemometer within the test section confirms the parabolic profile predicted for Poiseuille flow, with only minor deviations. In conjunction with the experimental testing, numerical simulations are performed to quantify probe support blockage effects on the velocity profile measurements. Test results validate the procedure for calibration of hotwire anemometers and development of forced convection heat transfer relations at stratospheric pressure conditions.