Numerical and Experimental Investigation of the Design of a Piezoelectric De-Icing System for Small Rotorcraft Part 2/3: Investigation of Transient Vibration during Frequency Sweeps and Optimal Piezoelectric Actuator Excitation

Abstract

The objective of this research project is divided in four parts: (1) to design a piezoelectric actuator based de-icing system integrated to a flat plate experimental setup, develop a numerical model of the system and validate experimentally; (2) use the experimental setup to investigate actuator activation with frequency sweeps and transient vibration analysis; (3) add an ice layer to the numerical model, predict numerically stresses at ice breaking and validate experimentally; and (4) implement the concept to a blade structure for wind tunnel testing. This paper presents the second objective of this study, in which the experimental setup designed in the first phase of the project is used to study transient vibration occurring during frequency sweeps. Acceleration during different frequency sweeps was measured with an accelerometer on the flat plate setup. The results obtained showed that the vibration pattern was the same for the different sweep rate (in Hz/s) tested for a same sweep range. However, the amplitude of each resonant mode increased with a sweep rate decrease. Investigation of frequency sweeps performed around different resonant modes showed that as the frequency sweep rate tends towards zero, the amplitude of the mode tends toward the steady-state excitation amplitude value. Since no other transient effects were observed, this signifies that steady-state activation is the optimal excitation for a resonant mode. To validate this hypothesis, the flat plate was installed in a cold room where ice layers were accumulated. Frequency sweeps at high voltage were performed and a camera was used to record multiple pictures per second to determine the frequencies where breaking of the ice occur. Consequently, the resonant frequencies were determined from the transfer functions measured with the accelerometer versus the signal of excitation. Additional tests were performed in steady-state activation at those frequencies and the same breaking of the ice layer was obtained, resulting in the first ice breaking obtained in steady-state activation conditions as part of this research project. These results confirmed the conclusions obtained following the transient vibration investigation, but also demonstrated the drawbacks of steady-state activation, namely identifying resonant modes susceptible of creating ice breaking and locating with precision the frequencies of the modes, which change as the ice accumulates on the structure. Results also show that frequency sweeps, if designed properly, can be used as substitute to steady-state activation for the same results.

Numerical and Experimental Investigation of the Design of a Piezoelectric De-Icing System for Small Rotorcraft Part 1/3: Development of a Flat Plate Numerical Model with Experimental Validation

“…This comprehensive study allowed to develop a numerical model for a simple flat plate and a better understanding and optimization of the actuators driving strategies in preparation for the design and instrumentation of an experimental piezoelectric-based de-icing system for small rotorcraft. The experimental setup designed is used in the next phase of the project to study transient vibration and frequency sweeps [22]. The numerical model is used in the third phase of the project by adding ice layers for numerical and experimental investigation of vibration-based de-icing [23], with the final objective of developing and integrating a piezoelectric actuator de-icing system to a rotorcraft blade structure.…”

“…The experimental tests were performed under the piezoelectric actuators excitation using sinusoidal signals at fixed frequencies to obtain steady-state mode deployment to compare with the numerical analysis results. The experimental results, given by the laser vibrometer software, present the upwards displacements in different shades of red, with lighter shades for higher magnitudes, and downwards displacements in different shades of green, also with lighter shades for higher magnitudes (see Figures 16,17,19,and 22). The operating voltage of the piezoelectric actuator was set to 200 Vpp, both experimentally and in the numerical model.…”

Electromechanical Resonant Ice Protection Systems: Energetic and Power Considerations

“…To study the initiation or propagation of ice fractures, it is necessary to have an approximate value of the cohesive tensile strength of the ice, of the adhesive shear strength of the ice with the substrate, and of the critical strain energy release rate. Although many experiments have been carried out to measure these values, there is a relatively wide range of ice strengths, and it is not easy to select a single value because ice strength depends on many factors: temperature [27][28][29], nature and roughness of the substrate [25], strain and strain rate [29,30], ice grain size [29], and flow speed [31]. Based on several articles [28,[32][33][34][35], the range of the ice tensile strength for fresh water is from [0.6-3] MPa, and the range of the ice adhesive shear strength for fresh water is from [0.2-1] MPa.…”

“…2). The ceramics were placed next to antinodes to get a high electromechanical coupling for these specific modes [25]. Another option would have been to place the ceramics in the middle of the sample where the stresses are also important.…”

Experimental Study of a Piezoelectric De-Icing System Implemented to Rotorcraft Blades

“…The present study represents an incremental improvement and complexification of previously presented experimental and Finite-Elements Analysis (FEA)-based numerical investigations where the principle of the proposed design method was demonstrated using a simple flat plate structure. The results of these experiments were published in [17][18][19], where a comprehensive literature study was presented, and the optimal integration and excitation of the actuators, the steady-state and transient vibration response and the stresses involved in icebreaking were extensively studied experimentally and numerically. In this new study, the developed and demonstrated concept was applied to a more complex structure, e.g., a rotating small-scale 22.9 cm (9 inches) long blade setup.…”