Uncertainty Assessment of Microwave Collection Efficiency Sensors in Direct Operational Mode

A microwave-based measurement system has been demonstrated in a low-speed academic wind tunnel for characterization of water collection along a model surface. The system has advantages over the dye-blotting paper system used in historical icing physics investigations, but the system must be implemented in icing wind tunnels that can reach flight-relevant speeds with characterized cloud properties, such as the Icing Research Tunnel (IRT) and the Adaptive Icing Tunnel (AIT) at NASA Glenn Research Center. The collection efficiency measurements are needed for validation of new icing prediction codes, such as GlennICE, and for more complex geometries than employed in past validation studies. Because of the importance of the expected data from the system and similar microwave collection efficiency measurement methods, the uncertainty of the water collection measurements made using the system in the NASA icing wind tunnels must be assessed. For this paper, a detailed uncertainty analysis of measurements using the microwave system in direct operational mode, or the operational mode without using a blotting media, is provided. Improvements made in the sensor design are described, and improved calibration methods and results are provided. Finally, preliminary measurements of water collection are presented for a new wind-tunnel model in direct operational mode, which is ultimately intended for use in the AIT, using the Liquid Film and Cloud Tunnel (LFACT) at Baylor University.