Design and Testing of an Erosion Resistant Ultrasonic De-Icing System for Rotorcraft Blades

Abstract : The goal of this research was to design a helicopter rotor blade lead edge that had high sand erosion resistance and was conducive to ultrasonic ice protection systems (IPSs). The first section of research tried to tailor the leading edge to promote ice interfacial transverse shear stress created by the ultrasonic vibration of piezoelectric actuators. Previous work done to tailor leading edges removed material from the inside of the cap. However, there were concerns about structural integrity and erosion wear when material was removed. A new system of adding material to the inside of the leading edge instead of removing material to create stress concentrations was researched for this thesis. Finite element analysis was used to determine the optimal locations for the discontinuities for the ultrasonic IPS. The discontinuities located in the optimal location are called Tailored Stress Concentrators (TSCs). Using the finite element results, it was determined that the best location for the TSCs were in regions of normally low stress in the baseline model before the addition of the TSCs. The addition of the TSCs creates stress concentrations as well as increased the original local maximum stresses. Initial models showed increases in average interfacial shear stress of 20%. Since the first FEM was not practical to construct as a bench top experiment, a second model was developed. Next, a bench top experiment and matching finite element model were built to validate the finite element analysis. The finite element model predicted a decrease of 9% in interfacial shear stress when TSCs were added to the bench top model. The bench top experiments confirmed the ineffectiveness of TSCs. There was no reduction in power required to de-ice when the TSCs were added to the bench top model.