An Experimental Study on Wind-Driven Runback Behavior of Water Droplets over Surfaces with Different Wettabilities*

An experimental study is performed to quantify the transient runback behavior of water droplet/rivulet flows as driven by boundary layer winds.  The experimental study is conducted in a low-speed wind tunnel available at Iowa State University. A suite of advanced flow diagnostic techniques, which include high-speed photographic imaging, digital image projection (DIP), particle image velocimetry (PIV), are used to quantify the transient runback behavior of wind-driven water droplets over test plates.   In addition to measuring the airflow velocity field around the wind-driven water droplets/rivulets, dynamic shape changes and stumbling runback motion of the water droplets/rivulets are also measured in real time in terms of water film thickness distribution, contact line moving velocity and wet surface area over the test plates with different wettabilities. The findings derived from the present study are very helpful to gain a better understanding about the important microphysical process pertinent to aircraft icing phenomena.