Robert J. Flemming

Prediction of Rotor Blade Ice Shedding using Empirical Methods

A methodology that couples computational fluid dynamics, computational structural dynamics, ice accretion models and ice shedding models is developed and applied to both isolated airfoils and rotors in forward flight, the latter with and without shedding. The individual modules are coupled to each other through industry-standard open file I/O methods, allowing the replacement of the individual modules with more advanced modules as technology matures. Ice shape results are presented and correlated with test data for a range of icing conditions. The torque rise associated with ice build-up on a UH-60A rotor in forward flight is modeled. Finally, results are presented for ice shedding phenomena for a small-scale model rotor. Reasonable correlation with test data is observed in the cases studied. BACKGROUND Despite decades of research on the phenomenon, rotor icing remains a major in-flight concern for many civilian and military helicopter operators. One particular facet of rotor blade icing receiving additional attention is shedding, more specifically self shedding. Self shedding occurs on a rotor blade when the aerodynamic and centrifugal forces on a section of ice exceed the structural adhesion forces holding the ice onto the blade. At the point when the adhesion force is exceeded, the ice is said to “shed” and separates from the rotor blade. After separation, the shed ice acts as a projectile and has the potential to strike components of the helicopter such as the tail rotor. In order to better evaluate the risks associated with self shedding, an accurate model must be developed for determining the conditions under which ice shedding will occur. This paper focuses on self-shedding mechanics and the development of a model, based on a combination of computational and empirical methods, for predicting shedding phenomena. The model presented is being developed as part of a larger initiative to investigate the trajectories of shed ice pieces and their potential for striking vehicle components. In order to meet this larger objective, the present model will first be used to predict shedding characteristics at particular operating conditions. At each operating condition analyzed, CFD and six degree-of-freedom modeling would then be used to determine the trajectories of shed ice pieces, as well as possible impact forces.