Challenges in Predicting Rotor Blade Ice Protection Coverage Extent using Alternate Flow Solver and Lewice3D 2011-38-0097

As the technology in rotor deicing matures, more programs are willing to engage in the certification of their helicopters for flight into icing conditions. The S-92A™ helicopter, AW139, V-22, and EC225 aircraft have been certified/qualified recently and are illustrative examples of such engagement. The state-of-the-art configuration definition of rotor ice protection systems that have been introduced into the western rotorcraft manufacturer's production line has been limited to electro-thermal deicing systems. System configurations may use either chordwise or spanwise shedding schemes and could differ in design and operation. Regardless of the selected design configuration, an analysis of the required extent of protection coverage must be performed unless one has access to data offering sufficient similitude in terms of airfoil geometry and flight conditions. The analytical path may be required to account for blade oscillation with continuously changing angles of attack through the entire azimuth, and continuously changing local velocities along the span of the blades, with local variation in the associated heat transfer and water drop collection efficiency.

While Lewice2D has been the code of choice for fixed-wing aircraft, its potential flow solver is quite limited when it comes to analyzing small-chord airfoils at high angles of attack and at local velocities approaching the speed of sound. Therefore, a method has been explored which utilizes a more applicable flow solver combined with the drop trajectory solver from the Lewice3D code. This combination has been selected as the best option in terms of accuracy and run time. Because of its availability and level of familiarization within Bell Helicopter, the FENSAP flow solver by Newmerical Technologies Inc. (NTI) was selected.

This paper presents the findings from the process used in establishing the coverage extent on a representative and readily available 206 helicopter tail rotor blade model. The model is to be tested in the NASA Glenn Research Center Icing Research Tunnel in support of the "High Fidelity Icing Analysis and Validation for Rotors" project which is funded by Vertical Lift Consortium (VLC) members Bell Helicopter, The Boeing Company, and Sikorsky Aircraft Corporation. Georgia Institute of Technology and NASA are active participants in the collaborative research effort, which is partially funded by the National Rotorcraft Technology Center (NRTC).