Actuator Bondline Optimization and Experimental Deicing of a Rotor Blade Ultrasonic Deicing System

Open Access
Author:
Overmeyer, Austin David
Graduate Program:
Aerospace Engineering
Degree:
Master of Engineering
Document Type:
Master Thesis
Date of Defense:
April 24, 2012
Committee Members:
  • Jose Palacios, Thesis Advisor
  • Edward Smith, Thesis Advisor
  • George A Lesieutre, Thesis Advisor
Keywords:
  • deicing
  • de-icing
  • icing
  • ultrasonic
  • electro-thermal
  • low power
  • ice protection
  • helicopter
  • rotor blades
Abstract:
The ultrasonic deicing concept has shown the ability to promote ice shedding in prior wind tunnel test efforts. In this prior research, the ultrasonic deicing prototypes failed due to actuator fracture and debonding from the host structure. The goal of this research is to advance the ultrasonic deicing technology towards a robust integrated system that achieves repeatable ice shedding. Finite Element Models (FEM) are used to predict the ultrasonic ice transverse shear stresses responsible for ice shedding. The FEM tools are experimentally validated and guidelines for mesh requirements are established. To accurately predict the dynamic response of the ultrasonic deicing system, the ultrasonic damping ratio is required. The ultrasonic damping ratio of a representative system excited at the first ultrasonic mode (~28.5 kHz) is measured to be 0.1885%. The FEMs predictions are validated by correlating experimental electro-mechanical impedance measurements. The discrepancy between the FEM predictions and experiments is determined to be 0.7% for the ultrasonic resonant frequency, 8% for the impedance and 5% for the out-of-plane velocities at this mode. The FEM tools are then utilized to guide the design of an optimized bondline between the PZT actuators and the host structure forming the ultrasonic deicing system. The optimized bondline provides the maximum ice interfacial transverse shear stresses and prevents debonding failures of the system. Details on the optimized system fabrication and integration are provided. The optimized bondline configuration is experimentally validated to increase the ice interface transverse shear stresses by 15% with respect to prior bondline approaches. To predict ice shedding due to excitation of an ultrasonic deicing system, an ultrasonic deicing rotor ice shedding prediction model is developed. The model couples a commercially available FEM with post processors to predict the ice shedding locations. The centrifugal, ice adhesion and cohesive forces are accounted for in the prediction of the shedding iv locations. The model is initially used to determine the critical ice adhesion area required to achieve ice shedding. If the critical ice adhesion area is reached, ice shedding is promoted. Based on a theoretical study for a generic rotor setup, (1.42 radius rotor, 400 RPM, 6.35 mm thick x 30.48 cm ice shape at the rotor tip) the critical ice adhesion area is determined to be 9%. To achieve the critical ice adhesion area, a multi-frequency excitation is suggested to distribute ice interfacial transverse shear stresses to avoid areas of ice bridging (local ice adhesion). The novel bondline approach is implemented to a rotor blade leading edge erosion cap representative structure (0.813 mm thick stainless steel leading edge). The test specimen is tested under impact icing and centrifugal environments (390 gs). The system is evaluated with a comprehensive set of rotational impact icing experiments within the FAR Part 25/29 Appendix C icing envelopes. Ice shedding was promoted for test cases throughout the icing envelope. The requirement for multi-frequency control is experimentally validated by promoting ice shedding when the critical ice adhesion area is met. For a single excitation frequency (no multi-frequency) with the same icing conditions and actuation input power, ice shedding was not promoted. The load power consumption of the deicing system is quantified to an average of 0.63 W/cm2. The deicing system is able to promote shedding of ice layers ranging from 1.4 to 7.1 mm in thickness for varying icing conditions within FAR Part 25/29 Appendix: C icing envelopes. During rotor impact icing tests, actuator fracture and debonding are not observed. Ice shedding experimental test cases are compared to the ultrasonic deicing shedding model with 2.3% and 4.5% error.