Rotating testing of a low-power, non-thermal ultrasonic De-icing system for helicopter rotor blades

Ultrasonic excitation has proven to provide ice interface transverse shear stresses exceeding the adhesion strength of freezer and wind tunnel ice to various metals, promoting instantaneous ice delamination. Prior proof-of-concept testing presented issues related to piezoelectric actuator cracking under ultrasonic tensile excitation, as well as actuator debonding from the host structure. The aim of this research is to provide solutions to the actuator reliability issues encountered during prior research and to perform rotor icing testing to validate the proposed solutions. Three different approaches are taken to solve the issues related with actuator failure during de-icing processes: custom designed controllers to ensure the excitation of desired ultrasonic resonance modes, compression only driving of the actuator, and optimization of actuator thickness. The novel driving conditions and geometry of the actuation system is modeled using finite elements and tested at the Penn State Adverse Environment Rotor Test Stand, where representative centrifugal forces are reproduced during ice impact testing. The ice protection capabilities of the ultrasonic de-icing was evaluated at twelve different icing conditions (over 1 hr. of active testing). The improved controller and actuator geometry demonstrated that ultrasonic de-icing techniques are able to delaminate thin layers (< 2 mm) of accreted ice under representative centrifugal forces without actuator failure. Ultrasonic ice protection under rotating environments is presented, as thin layers of ice were continuously delaminated from the leading edge of the blade. The recorded power requirements averaged 0.37 W/cm² (2.4 W/in²) (90% reduction with respect to electro-thermal de-icing).