Icing Prevention by Ultrasonic Nucleation of Supercooled Water Droplets in Frontof Subsonic Aircraft

摘要

Experiments were performed in the NASA Lewis Research Center (LeRC) IcingResearch Tunnel (IRT) to explore the possible application of an icing prevention technique. This technique is based on nucleation ice crystallization in supercooled cloud droplets upstream of the impingement surface and relying on evaporative cooling to remove the latent heat of fusion from the droplet so that it can completely freeze before striking the solid surface. Ice accretion on the impingement surface was measured to quantify the changes due to induced nucleation. A flow duct was designed to provide a uniform, parallel flow from the nucleation excitation volume to the test surface, a simple symmetric airfoil. The distance between the excitation volume and the airfoil in the flow duct could be varied, but the maximum length of over 2 m was chosen to maximize the time for freezing. Ice accretion was measured over a range of tunnel parameters, including tunnel velocities of 50-100 mph and temperatures from 0 to -36 F. At colder temperatures, spontaneous freezing of supercooled droplets led to reductions in observed ice accretion. However, the range of active nucleation parameters explored in this set of experiments had no measurable effect on ice accretion on the subject airfoil. Suggested future work includes expanding the measurement parameter space and obtaining static measurements in a cloud chamber.