Book Description

"Encounters with Supercooled Large Droplets (SLD) pose a danger to aircraft, as they can cause ice accretion beyond the reach of ice protection systems. In-flight icing effects must meet the regulations of airworthiness authorities in order for a new class of aircraft to obtain a type certification. Since flights into natural icing conditions and wind/icing tunnel tests cannot fully explore the SLD icing envelope, Computational Fluid Dynamics (CFD) has become an indispensable tool for assessing in-flight icing effects. However, the SLD modules of such in-flight icing simulation codes rely on empirical data or extrapolation from low-speed experiments. This thesis aims to develop a multiphase Smoothed Particle Hydrodynamics (SPH) solver for conducting "numerical experiments" of SLD impingement at flight speeds, to ultimately yield a macroscopic SLD model that can be embedded into in-flight icing simulation codes.SPH is a mesh-free CFD method suitable for SLD problems as it can handle complex interfaces and model multi-phase physics. In the multiphase SPH framework presented here, the inviscid momentum and energy equations are solved for flow and heat transfer, along with an equation of state linking pressure and density. A multiphase model is used to represent interfacial flows, and a fixed ghost particle method to enforce boundary conditions. Artificial viscous and diffusive terms are employed to smooth physical fields and decrease numerical instability, while a particle shifting technique is used to alleviate anisotropic particle distribution. Several numerical techniques are proposed to model the complex physics of SLD impingement such as a contact angle model to represent the non-wetting properties of hydrophobic surfaces, a latent heat model to account for phase change and a supercooled solidification model to capture dendritic freezing. The solver is validated against a series of experimental results, showing good agreement. It is then first applied to droplets impinging at flight speeds on a water film to study the effects on the post-impact water crown of droplet speed and diameter, surface tension, water film thickness, and impact angle. Droplets impacting on cold solid surfaces are then simulated to study freezing time and post-impact ice particle distribution for a range of speeds and impact angles. Following this, an improved contact angle model is used to study the interaction between droplets and hydrophobic/superhydrophobic coatings. Finally, SLD impinging on ice surfaces are studied via a supercooled solidification model, with supercooling degree and impact speed effects on residual ice analyzed. This thesis thus develops an SPH numerical framework capable of simulating SLD impingement and solidification at in-flight icing conditions. It provides a toolset for comprehensive parametric studies of SLD impingement, paving the way for a macroscopic SLD model for in-flight icing simulation codes"--