Modification and Tests of Particle Probe Tips to Mitigate Effects of Ice Shattering

Ice particle shattering may significantly contaminate measurements taken by airborne particle probes in ice clouds. Environment Canada and the NASA Glenn Research Center (GRC) undertook efforts to modify and test probe tips in order to mitigate the effect of shattering on measurements. This work presents an overview of the results obtained during the design work on the particle probe arm tips. Even though this work was focused on the modifications of three of the probes-Particle Measuring Systems Inc. (PMS) Forward Scattering Spectrometer Probe and optical array probe, and Droplet Measurement Technologies (DMT) Cloud Imaging Probe-the outcomes of this work bear a general character and are applicable to other similar instruments. The results of the airflow analysis around the probe's housing and the simulations of particle bouncing from the probe tips are discussed here. The originally designed and modified tips were tested in a high-speed wind tunnel in ice and liquid sprays. The ice particle bouncing processes as well as patterns of water shedding over the surface of the probes arms were studied with the help of a high-speed video camera. It was found that at aircraft speed, after bouncing from a solid surface, ice particles may travel several centimeters across the airflow and bounce forward up to 1 cm. For the first time it has been directly documented with high-speed video recording that the sample volumes of particle probes with the originally designed tips are contaminated by shattered and bounced particles. A set of recommendations on the existing modification and the design of future particle probe housings is presented.