Comparison of Liquid Water Content Measurement Technquies in an Icing Wind Tunnel

Abstract : This paper compares the results of liquid water content measurements by various means in an icing wind tunnel. The techniques/instruments tested are the icing blade, a single rotating cylinder, the Johnson-Williams and CSIRO-King hot-wire probes, the Nevzorov LWC/TWC probe and the liquid water content calculated from the combined droplet distributions of two droplet sizing probes - the Forward Scattering Spectrometer probe and the Optical Array probe. A large range of icing conditions was used for this study. The liquid water content ranged from 0.1 to 1.25 g/cu m and the median volumetric droplet diameters (MVD) ranged from 10 to 270 micrometers. Airspeeds of 50 to 250 mph (22 to 112 m/s) were used. This study shows the degree of agreement between the various liquid water content measurement methods over the normal cloud MVD range of 10 to 50 micrometers and over several supercooled large droplet (SLD) conditions. It shows that the Nevzorov LWC/TWC instrument has the potential for measuring the LWC in SLD clouds as well as normal droplet size cloud conditions. It reveals a large disagreement between the droplet sizing probe results and the other methods. The implications and possible causes of this disagreement are discussed. Recommendations for additional investigations to resolve disagreements are included.