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Photograph by caribb on flickr, available under a. license. . Two distinct types of ice accretion have been observed: Rime-ice accretions A dry, opaque and milky-white ice deposit with a density lower than that of the water in the impinging droplets. It usually occurs at low airspeeds, low temperatures, and low 's. In

Compared to conventional icing additional droplet phenomena have to be accounted for in icing caused by supercooled large droplets (SLD) such as splashing, rebound, breakup and deformation. In this study the effect of the presence of a thin liquid film of water on the surface has been investigated. This liquid layer can arise when SLD droplets freeze only partially following impact on the airfoil. The effect of the liquid film is simulated by using the wall shear stress and by assuming a linear velocity profile in the liquid layer. The shear stress is calculated by coupling an integral boundary-layer method to a potential flow method. An improved splashing model has been implemented in the existing computational method. This splashing model consists of a deposition model that accounts for splashing during impact of droplets on a liquid layer. In an extension to this model different solidification models have been investigated to estimate the time of solidification of a liquid splat produced on the surface after impact. One is a planar solidification model which is described by the Stefan problem for heat conduction and which is mostly controlled by diffusion. The second model is based on dendritic solidification, which is rapid and governed by kinetics. The results of the deposition model on SLD ice accretion are compared with data from experiments on a NACA-23012 airfoil and on a NACA-0012 airfoil. Good agreement is found. Nomenclaturec Chord, m C p Specific heat d Diameter, m f D Drag force per unit mass, N/kg g Gravitational acceleration, m/s 2 h Height, m K Cossali splashing parameter k Thermal conductivity, W/mK L Latent heat, J/kġ m in Inflowing mass flow rate per meter span, kg/m 3 s n Unit normal vector N h Number of droplets hitting the splaṫ q w Volumetric flux of impacting droplets, m 3 /m 2 s T Temperature, K t Time, s t solid Solidification time, s u Velocity, m/s * PhD student, faculty of Engineering Technology, group Engineering Fluid Dynamics † PhD student, faculty of Engineering Technology, group Engineering Fluid Dynamics, presently Zeton B.V.,

A computational method is presented that given the flow solution computes ice accretion on multiple-element airfoils in specified icing conditions. The numerical simulation method (Droplerian) uses an Eulerian method to determine the droplet trajectories and distribution of the Liquid Water Content (LWC). To solve the equations for the droplet trajectories and liquid water content distribution, Droplerian uses a Finite Volume Method for unstructured grids. Through the droplet velocities and Liquid Water Content at the surface of the airfoil configuration the droplet catching efficiency is calculated. The droplet catching efficiency and droplet velocities at the airfoil surface are input for the icing model, which is based on Messinger's model for ice accretion. The method includes a multi-disperse droplet distribution with an arbitrary number of droplet bins and a droplet splashing model. For a single-element airfoil a good agreement is found with measured catching efficiencies and with the ice shapes predicted by other computational methods. For increasing droplet diameter the agreement with experimental results deteriorates. The application of the method to a three-element airfoil is described. The comparison of the catching efficiency predicted by both the Droplerian method and a Lagrangian method (2DFOIL-ICE) is good. The agreement of predicted ice accretions with available experimental data is reasonable.

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