Experimental Study of Large Droplet Splashing and Breakup

Abstract

An experimental investigation of droplet impingement in the proximity of clean and iced airfoils was conducted at the NASA Glenn Droplet Imaging Flow Tunnel (DrIFT). Droplets were released using a mono-dispersed droplet generator at the tunnel inlet and were accelerated by the tunnel contraction prior to impingement on the airfoil surface. The main objective of the study was to develop and refine visualization techniques to improve understanding of large droplet splashing and breakup phenomena. It is hoped that, with better measurement techniques, more accurate physical models can be developed for the simulation of ice accretions due to supercooled large droplets (SLD). The DrIFT tunnel inlet and contraction sections were replaced by a specially designed inlet contraction section to reduce potential droplet breakup near the tunnel throat area and to minimize droplet dispersion in the test section. The original test section was also replaced with a new test section to allow better optical access for imaging droplet splashing and breakup. These tunnel improvements allowed acceleration of droplets between 40 and 370 μm in diameter to velocities of up to 135 mph without droplet breakup. The process of droplet impingement, splashing and breakup were recorded using two cameras, a Phantom v7 high-speed digital camera and a PI MAX CCD camera. The Phantom camera was also used to determine the droplet sizes produced by the mono-dispersed droplet generator.