Chapter 17 Experimental and Numerical Aeroelastic Analysis of Airfoil-Aileron System with Nonlinear Energy Sink Claudia Fernandez-Escudero, Miguel Gagnon, Eric Laurendeau, Sebastien Prothin, Annie Ross, and Guilhem Michon Abstract Recent studies on nonlinear passive absorbers present high control efficiency for broadband frequency range with low added mass. This work presents a configuration of an airfoil typical section where the flap is considered as a Nonlinear Energy Sink (NES), which adds zero mass and has a cubic stiffness. An aeroelastic test-bench was created and characterized for linear and nonlinear structural configurations and tested in a subsonic wind-tunnel experimental campaign. The strongly nonlinear hardening stiffness is obtained by using linear springs and geometric nonlinearities. For the nonlinear tests, several Limit Cycle Oscillation (LCO) and subcritical and supercritical Hopf bifurcations were observed. Numerical analysis was also carried out for both linear and nonlinear cases using: Unsteady Vortex Lattice Method (UVLM) and Theodorsen theory (both low fidelity), Euler (medium fidelity) and Reynolds-Averaged Navier Stokes (high fidelity) methods. The numerical methods present good agreement, within the limits of each approach, and correspond with the experimental data. Using the NES, a gain of flutter speed is reached compared to the linear flap restoring force configuration. Keywords Aeroelasticity · Unsteady aerodynamics · Flutter · LCO · Nonlinear dynamics 17.1 Present Work An important phenomenon encountered in dynamic aeroelasticity is flutter. If there are no sources of nonlinearities the system can only experience classic flutter which is defined as self-excited vibration of the structure due to energy extraction of the incident airflow. This generally results from the coalescence of two structural modes: pitch and plunge, which reach the same vibration frequency. If the speed becomes greater than the flutter speed, the amplitude of the movement grows exponentially causing structural failure [1]. The presence of nonlinearities can change dramatically the observed behaviour as other phenomena, such as limit cycle oscillations (LCOs), can appear in the system’s response. During a LCO, the vibration reaches a finite amplitude which remains constant unless the wind speed changes. LCOs can be observed in subcritical or in supercritical regime once flutter speed is exceeded [2]. In order to increase the systems flutter speed, active methods (energy input) are very efficient but can be obsolete in emergency cases (ie. lack of power). Tuned Vibration Absorbers (TVA) are a good alternative and are already widely used in civil engineering [3]. The classic linear TVA is simple and efficient but only close to a single frequency. The main drawback is the inefficiency to control an oscillator whose natural frequencies changes with the wind speed (ie. aeroelastic wing). Semiactive strategies could solve this problem but the energy dependency is still present. This is the reason why some research studies focus on Nonlinear Tuned Vibration Absorber (NLTVA) [4]. The Nonlinear Energy Sink (NES) [5] is a NLTVA with C. Fernandez-Escudero ISAE-Supaero, Toulouse, France Polytéchnique Montreal, Montreal, QC, Canada S. Prothin ISAE-Supaero, Toulouse, France M. Gagnon · E. Laurendeau · A. Ross Polytéchnique Montreal, Montreal, QC, Canada G.Michon Université de Toulouse, ICA, CNRS, ISAE-Supaero, Toulouse, France © Society for Experimental Mechanics, Inc. 2020 G. Kerschen et al. (eds.), Nonlinear Structures and Systems, Volume 1, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-12391-8_17 133
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