Cool computer model predicts ice build up on aircraft

01 Jun 2005

There’s more to ice than that welcome tinkle in a tall drink.

For aircraft engineers, ensuring that their designs do not lead to unforeseen and detrimental ice build up around flying surfaces and engines is a major challenge. The ATC has pioneered a new computer model that can predict how ice accumulates on aircraft surfaces. The results are already saving the company large sums of money by avoiding expensive flight trials.

It’s vital to understand the way that ice accumulates and breaks away when designing aircraft structures. The same is true for rotors and other surfaces in jet engines. Small changes caused by ice in the path taken by air flowing over a wing, propeller or helicopter blade can greatly affect the aerodynamic forces causing loss of lift and controllability. Lumps of ice breaking away could spell disaster if sucked into engines.

The ATC is now in a leading position to predict the build-up of ice in airflow by combining a model of ice accretion with Computational Fluid Dynamics codes used routinely in aerodynamic design. Until now, no means existed for dealing with the complex, 3-D shapes now encountered in modern aerospace engineering. Once the likely icing conditions have been understood, the necessary steps can be taken to mitigate the effects either through changes to design of airframe components or the introduction of anti-icing measures.

Results from the work have already been used to great effect in the Nimrod and Tornado programmes. In a recent case with CS&S, the model was a decisive factor in assessing the necessity for anti-icing measures on a particular aircraft. The use of the model removed the need for flight trials saving the company a cool £300,000

The calculations take into account the trajectories of water droplets in the airflow and predict how water will impact, flow and then freeze on the surfaces. “With our project partners, we have developed novel algorithms for determining, and refining, droplet start locations. The code can include the effect of droplet splash and a whole spectrum of droplet sizes. The unsteady development of the water flow and the rate, type and location of ice is then simulated.” says Andy Press, aerodynamicist at the ATC.

The model has taken six years to develop and is moving into the final phase of refinement and validation. The prediction capability is being extended by including anti-icing and iceshedding models. It allows the effects of icing conditions to be understood for a wide range of airframe components and enhances the specification, design and testing of ice protection equipment. A database using experience gained from experiments is being built into the software to allow estimation of iceshedding events.

The ATC along with partners AIRBUS UK, Rolls-Royce, Dunlop Aerospace, Westland Helicopters, QinetiQ and Cranfield University, have carefully formulated the model so that it can be combined with many standard computational fluid dynamic codes and presentation software used widely throughout industry.

During the next two years, extensive validation studies are planned by the partners using comparisons to existing experimental and predicted data. The work will also feature in a MASS programme aimed at reducing the costs of service provision to the RAF.

The work is part funded under the DTI CARAD programme.