Enhancement of Ultrasonic De-Icing via Tone Burst Excitation

Abstract

Previous ultrasonic de-icing research on rotorcraft has demonstrated that applying multifrequency burst actuation schemes has increased the ice protection area coverage of the system. The physical mechanisms responsible for this increase in de-icing performance are modeled using finite elements and tested using both freezer ice and impact ice in the Adverse Environment Rotor Test Stand facility at the Pennsylvania State University. Freezer ice was tested using a 0.035-in.-thick (0.889-mm-thick) titanium grade 2 plate. Impact ice testing was conducted using a 0.035-in.-thick (0.889-mm-thick) stainless steel NACA 0015 airfoil structure (16 in. or 40.64 cm chord). It is proven that the increase in ice shedding area when using multifrequency tone bursts is due to the transient nature of the excitation and not the multimode control of the structure at varying frequencies surrounding the resonance of the structure. During bench-top testing using freezer ice, ultrasonic burst actuation techniques that exploit transient vibrations showed to increase the de-icing performance (as quantified by the ice shedding area) by a factor of 4 when compared to continuous actuation methods. The benefits of tone burst actuation were as large as 10 times that of continuous frequency actuation when testing rotor impact ice affected by centrifugal loads.