Experimental Measurement of Frozen and Partially Melted Water Droplet Impact Dynamics

Abstract

High-speed video of single frozen water droplets impacting a surface was acquired. The frozen particles had a diameter ranging from 0.4 mm to 0.9 mm and impacted at velocities varying from 140 m/sec to 309 m/sec. The technique used to freeze the droplets and launch the particles against a surface is described in this paper. High-speed video was used to quantify the ice accretion area to the surface for varying impact angles (30⁰, 45⁰, 60⁰), and impacting velocities. An oxygen /acetylene cross-flow flame used to partially melt the traveling frozen particles is also discussed. A linear relationship between impact angle and ice accretion is identified for fully frozen particles. The slope of the relationship is affected by impact speed. Higher impact angles closer to perpendicularity between the surface and the particle trajectory, e.g. 60⁰, exhibited small differences in ice accretion with varying velocities. Increasing velocity from 161 m/sec to 259 m/sec nearly doubled the ice accretion area at a shallower impact angle of 30⁰. The increase accretion area highlights the importance of impact angle and velocity on the accretion process of partially melted ice crystals. It was experimentally observed that partial melting was not a pre-requisite for accretion at the tested velocities when impact angles of 45⁰ and 30⁰ were used. Partially melted droplets using just 0.0023 Joules of energy also doubled the ice accretion area. The partially melted state of the particles and a method to quantify the percentage increase in the ice accretion area is also described in the paper.

Plans and Preliminary Results of Fundamental Studies of Ice Crystal Icing Physics in the NASA Propulsion Systems Laboratory

“…During this time period, a NASA and NRC collaboration produced several papers on the topic of fundamental ICI research 7,[16][17][18][19] . Other efforts during this time period related to the fundamentals of ICI include work on ice particle impact physics at NASA 20 , Penn State University (PSU) 21 , and a collaboration with PSU and the John Hopkins Universities Applied Physics Lab 8 . In 2015, the NASA engine icing work was transitioned to NASA's Advance Air Transport Technology Project under a new subproject called Advanced Aircraft Icing (AAI).…”

Three-Dimensional Trajectory and Impingement Simulation of Ice Crystals Considering State Changes on the Rotor Blade of an Axial Fan

“…They estimated the temporal variation in the size of ice crystals sucked into the engine using this model. Palacios et al [24] conducted experiments in which melted ice crystals impacted an aluminum wedge. The results showed that the ice accretion area on the surface expanded with increases in impact angle, impact velocity, and melting ratio.…”

Ice crystal impact onto a dry solid wall. Particle fragmentation

“…In this context, studies dealing with the impact process of small ice particles are very limited. Palacios et al [16] investigated the impact process of fully frozen and partially melted spherical ice particles with diameters between 0.4 and 0.9 mm. The impact velocities varied between 140 and 309 m s −1 , and the impact angle was set to 30 • , 45 • or 60 • .…”