Liquid Water Content Instrumentation Study at the NRC AIWT

The National Research Council Altitude Icing Wind Tunnel liquid water content calibrations have historically relied on a 2.4 mm diameter rotating cylinder for drop sizes up to 50 μm and a 6.2 mm diameter rotating cylinder for drop sizes from 50 μm to 200 μm. This study compares the facility calibration, derived from rotating cylinder measurements, to water content measurements from the Science Engineering Associates Multi-Element Probe and the National Research Council Compact Iso-Kinetic Probe over a range of airspeeds and drop sizes. The data show where the rotating cylinder measurements may start to underestimate the liquid water content (LWC), possibly due to splashing at higher airspeeds and drop sizes. The data also show that the LWC read by the Multi-Element Probe is higher than that provided by the rotating cylinders, and the Compact Iso-Kinetic Probe (CIKP) reads higher than both other methods. These trends are consistent with instrumentation comparison data from other icing wind tunnels. The study examines the effects of aerodynamic blockage on the probe measurements and the effects of placing the CIKP reference humidity sensor at different positions relative to the icing cloud. Overall, the data do not support changing the AIWT LWC calibration method from the rotating cylinder at this time.