Adverse meteorological conditions often contribute to the formation of ice on aircraft wing section, engine nacelle and other parts leading to the loss of lift coefficient and increase in drag coefficient affecting aircraft control and stability. This paper addresses the problem of in-flight icing on an asymmetric aerofoil under three different ambient and cloud conditions. The study involves prediction of the leading-edge ice thickness using a numerical model developed from the mass and energy conservation law and Messinger freezing fraction model at the same Reynolds number. Later on, degradation in the aerodynamic performance of the iced aerofoil was also investigated using the computational fluid dynamics (CFD) technique, taking the flow field around a 2D aerofoil geometry into account. The aerodynamic study indicates that cumulus clouds embedded with stratified clouds contribute to the formation of mixed ice on aerofoil leading edge and causes the worst icing scenario reducing the lift coefficient to 90% and increasing the drag coefficient to 800% for the same ambient conditions.

In glaze ice conditions, beads on the surface usually grow to form roughness elements through coalescence, finally resulting in enhancement of local collection efficiency. However, the effects of roughness elements due to freezing of beads are not reflected on the local collection efficiency in CFD icing simulations. This is problematic for predicting the resultant ice shape, which may lead to inaccurate aerodynamic performance and load distribution. The aim of this study is to propose a macroscopic icing model which can reflect bead microscopic phenomena using the Eulerian approach. To this end, a correction was made for collection efficiency by introducing a novel parameter - the effective impinging angle- which is the angle to calculate the local collection efficiency depending on the physical state of surface. It is assumed that the parameter related to the contact angle represents the state of beads. The computational icing analysis of airfoil was performed using the proposed model both in the rime condition and glaze conditions. The results show that the icing characteristics in the feather region is captured with enhanced accuracy in both conditions.

Following the B777 accident at Heathrow in 2008, the certification authorities required Boeing, Airbus, and Rolls-Royce to conduct icing analysis and tests of their Rolls-Royce Trent engined aircraft fuel systems. The experience and the test data gained from these activities were distilled and released by Airbus to the EASA ICAR project for research and analysis. This paper provided an overview of the Airbus ice accretion and release tests. Brief narratives on the test rigs, the test procedure and methodology were given and key findings from the ice release investigations were presented. The accreted ice thickness was non-uniform; however, it is found typically c. $\mathrm{2\;\mathrm{m}\mathrm{m}}$ thick. Analysis of the accreted ice collected from the rig tests showed the ice was very porous. The porosity is very much dependant on how the water was introduced and mixed in the icing test rigs. The standard Airbus method produced accreted ice of higher porosity compared to that produced by the injection method. The porosity of the accreted ice from Airbus icing investigations was found to be c. 0.90. The relationship of permeability with porosity was inferred from published data and models for freshly fallen snow in the atmosphere. Derived permeability $\mathrm{7.0\times 10^{-9}\;\mathrm{\mathrm{\mathrm{m}}^{\mathrm{2}}}}$ was then applied in the CFD analysis of pipe flow with a porous wall lining to determine the shear stress on the accreted ice. It showed that 25%, 50% and 75% of the accreted ice has interface shear strength of less than $\mathrm{15.3\;\mathrm{Pa}}$, $\mathrm{20.7\;\mathrm{Pa}}$ and $\mathrm{26.1\;\mathrm{Pa}}$, respectively.