Over the past few decades, the subject of aircraft icing has gained more and more attention from the FAA in the United States, which has dedicated one full section to the certification of aircraft under icing conditions.

Icing occurs when liquid droplets in the air strike the front of the oncoming wing and either freeze on contact or flow along the surface and then freeze. Many factors, which can be difficult to re-create in a laboratory setting, influence the likelihood that ice build-up will occur.

The main method used by aircraft manufacturers to certify their aircraft is to test a model of the aircraft in simulated icing conditions using an icing tunnel. Another method is to perform a tanker test, where a tanker aircraft sprays water droplets onto a following aircraft. Since both of these tests are expensive and time consuming, computational methods are gaining in popularity. In FLUENT, the collection efficiency, a measure of the amount of droplets in the oncoming air that strike the aircraft, can be obtained using the discrete phase model (DPM), which tracks the trajectories of droplets in the Lagrangian frame.The Eulerian multiphase model can also be used, in which the droplets and air are treated as separate fluids. The collection efficiency is computed through the use of a user defined function (UDF).

Icing on the front and under-side of a commercial aircraft wing with the high lift devices extended, displayed using contours of collection efficiency

An anti-ice system that uses engine bleed air to heat the wing skin using a linear array of jets.