Global ultrasonic shear wave anti-icing actuator for helicopter blades

An optimized ultrasonic shear wave actuator is designed and fabricated to trigger anoptimum anti-icing ultrasonic mode that generates large modal interface shear stress concentrations that would allow global anti-icing of an aluminum plate (1 MHz frequency, 12 Km/s wave propagation phase velocity). The system is formed by a 2 mm aluminum pate and 1.5 mm ice layer. The phase velocity of the triggered mode is controlled by the width and spacing of 4 shear patches attached to the aluminum plate. The aluminum plate had wavelength-multiple dimensions to eliminate destructive interference at its boundaries. When the system is excited at this optimum ultrasonic mode with large modal interface stresses, the system does not influence the accreted ice. 800 Watts of input energy is applied to theshear actuators. Even though a large modal interface stress ultrasonic mode is triggered,the actuator does not have sufficient authority to provide large enough interface stresses to affect ice bonding. The new system, when excited at the resonance of the shear patches (130 KHz), melts well accreted ice up to 18 cm away from the actuator region center (80% of the overall plate surface). With the described actuator - aluminum plate configuration, an increase on affected ice bonding region of 60% is introduced with respect to prior tested shear antiicing actuators. Minimization of destructive boundary effects due to the wavelength-multiple dimension of the aluminum plate is the reason for the increase in de-iced area. The vibration promotes ice adhesion failure 45 seconds after the excitationis introduced, as 10% of the shear stress failure of ice (0.03 MPa) is applied. To experimentally demonstrate the theoretical concept of ultrasonic modes with high interface shears stress concentration coefficients, which are able to instantaneously remove thin layers of well accreted ice a 42 KHz, 800 Watt Lamb wave transducer is applied to several aluminum plate - ice thickness configurations. Analytical predictions and correlation with proof-of-concept experiments performed with the ultrasonic Lamb wave actuator support the proposed theoretical analysis to design future global anti-icing actuators for helicopter rotor blades.