Characteristics of Wind-Driven Runback Droplet/Rivulet Flows: Part 1 - Experiment Investigation with Simultaneous DIP and PIV Measurements

A better understanding of the characteristics of wind-driven water droplet/rivulet flows and their resultant effects on the development of boundary layer airflow is crucial for the safety of aircraft, UAVs, and rotorcraft operation under rainfall and icing conditions. Previous numerical studies suggest that idealized droplet or particle-like disturbances can disrupt the boundary layer airflow by creating turbulent spots, wedges, or unstable low-speed streaks. Given this background, an integrated experimental (part #1) and numerical (part #2) study is conducted to investigate the transient behavior of wind-driven droplet/rivulet flows and their effects on the development of boundary layer airflow over a test surface. In part #1, a systematic experimental campaign was conducted to quantify the dynamic runback behavior of wind-driven droplet/rivulet flows over a flat plate with different incoming wind speeds and water droplet sizes. While a novel Digital Image Projection (DIP) technique was used to quantify dynamic shape changes of the wind-driven droplets/rivulets over a flat plate, the corresponding characteristics of the boundary layer airflow over the test plate are measured simultaneously by using a high-resolution Particle Image Velocimetry (PIV) system. The temporally and spatially resolved DIP measurements of the dynamic shape changes of wind-driven droplet/rivulet flows are correlated to the simultaneous PIV results of the boundary layer airflow over the test surface to elucidate the underlying physics.