Ultrasonic De-Icing of Wind-Tunnel Impact Icing

Ultrasonic excitation has proven to provide ice-interface transverse shear stresses exceeding the adhesion strength of freezer ice to various metals, promoting instantaneous ice delamination. Wind-tunnel impact ice presents challenges that are not encountered when removing freezer ice. The low-power, nonthermal ultrasonic de-icing concept is investigated under impact-icing conditions in an icing wind tunnel. In this research effort, ultrasonic actuator disks excite isotropic plates and airfoil-shaped structures that are representative of helicopter leading-edge protection-cap shapes. Off-the-shelf ultrasonic actuators are used to create ice-interface shear stresses sufficient to promote instantaneous ice delamination of thin layers of impact ice (less than 3 mm thick). A steel plate of 30.48 cm x 30.48 cm x I mm was actuated by three lead zirconate titanate disks excited at their ultrasonic radial mode. The ultrasonic vibration introduced transverse shear stresses that prevented ice formation on top of the actuator locations for a fraction of the power required with electrothermal systems used in helicopter rotor blades (0.18 W/cm(2) vs 3.8 W/cm(2)). Experiments also showed ice delamination in areas of the plates where transverse shear stresses were concentrated. As ice thicknesses reached a critical value of approximately 1.2 mm, ice debonded from those steel-plate areas. A model of the three disk actuated steel plate was created and correlated with experimental results observed during impact-icing test experiments. Both, the predicted ultrasonic modes of the system and the ice-shedding areas agreed with experimental results. In addition, a second set of experiments involving NACA 0012 airfoil-shaped structures were conducted. Actuators located on the top and bottom surfaces of the leading-edge cap were actuated with an input power as low as 200W (32 kHz ultrasonic mode). Thin layers of ice (less than 2 mm thick) constantly delaminated from the leading edge of the airfoil on those regions where stress concentrations were predicted.