Making a splash: from high speed droplet impact to a novel methodology for water retention calculation

Supercooled droplets, found in the atmosphere at temperatures below 0◦ C, have been known to significantly affect aircraft performance and have been the cause of numerous incidents in the last few decades. Even in seemingly dry conditions, aircraft may interact with high liquid water content clouds in the ascent or in the descent stages of the flight. Should this be the case, in a matter of seconds the fuselage and wings come into contact with a large number of supercooled droplets, each splashing onto the surface and leaving behind a quantity of fluid (see Figure 1).

At the heart of the described scenarios we find multi-fluid flow elements such as drops and thin liquid films. Motivated by practical implications such as flight control and reliability, de-icing procedure design, efficient fuel consumption and aircraft certification, in this body of research we turn to analytical and numerical techniques in multi-phase fluid dynamics.

We have developed a new methodology for the calculation of water collection efficiency on aircraft surfaces. The approach incorporates the detailed fluid dynamical processes often ignored in this setting, such as the drop interaction with the surrounding air flow, drop deformation, rupture and coalescence, as well as the motion of the ejected microdrops in the computational domain (see Figure 2 and related videos above).

Direct numerical simulations using the volume-of-fluid technique are performed using modelling assumptions which enable us to take advantage of the disparity of lengthscales in the system. The analysis shows a high degree of flexibility and can be used efficiently when considering changes in geometry (aircraft design), flow conditions and cloud characteristics.

This research has resulted in further ramifications into fundamental aspects of the drop impact problem, such as the detailed dynamics involved in liquid-liquid impact at moderate velocities, relevant to environmental conditions.