A Nonlinear Controller for Flutter Suppression: from Simulation to Wind Tunnel Testing

Abstract

Active control for flutter suppression and limit cycle oscillation of a wind tunnel wing section is presented. Unsteady aerodynamics is modelled with strip theory and the incompressible two-dimensional classical theory of Theodorsen. A good correlation of the stability behaviour between simulation and experimental data is achieved. The paper focuses on the introduction of a nonlinearity in the plunge degree of freedom of an experimental wind tunnel test rig and the design of a nonlinear controller based on partial feedback linearization. To demonstrate the advantages of the nonlinear synthesis on linear conventional methods, a linear controller is implemented for the nonlinear system that exhibits limit cycle oscillations above the linear flutter speed. The controller based on partial feedback linearization outperforms the linear control strategy based on pole placement. Whereas feedback linearization allows to suppress fully the limit cycle oscillations, the pole placement fails to achieve any significant reduction in amplitudes.

Experimental Nonlinear Control for Flutter Suppression in a Nonlinear Aeroelastic System

“…The coefficients of the above aeroelastic system are detailed partly in [6] and partly in the Appendix at the end of this manuscript. This allows one to setup the numerical model starting from the baseline aeroelastic parameters of the pitch-plunge aerofoil described later on.…”

“…Theoretical work and numerical modelling have primarily been on controlling smooth and non-smooth nonlinear aeroelastic systems by Da Ronch et al [6] and Jiffri et al [7]. More recent experimental developments include measurement of the aeroelastic system's parameters and open-loop investigations, experimental testing conducted on piezo-MFC bimorph actuation for morphing wing technology and the development and manufacture of a flexible wing for aeroelastic testing by Fichera et al [8].…”

“…Numerical simulations of closed-loop control presented in [6] are implemented experimentally, utilising previously obtained experimental measurements and open-loop results. §II describes the experimental setup, which is followed by a detailed description of the low-order numerical model ( §III) used in conjunction with the experimental work.…”

An Adaptive Aeroelastic Control Approach using Non Linear Reduced Order Models

“…As a continuation of this work, the authors of this investigation performed partial feedback linearization for a numerical model corresponding to a low speed wind tunnel model with a nonlinearity in the plunge degree of freedom. 7 It was shown that the nonlinear controller outperforms a linear control design based on pole placement as the latter fails to achieve any significant reduction in the amplitude of the LCO. Also, optimal control has been tested for flutter suppression, for example, Huang et al 8 designed a Linear Quadratic Gaussian control that takes into account a control input delay and applied the control at an experimental wind tunnel model for flutter suppression.…”

Model Order Reduction for Control Design of Flexible Free-Flying Aircraft

“…Recently, a nonlinear control design methods was tested for a nonlinear experimental wind-tunnel rig for LCO suppression and was compared against conventional linear techniques . 13 Ideally though, a controller that can adapt during changes of the flow conditions such as airspeed or density is desired. Recent advances in adaptive control and especially in L 1 adaptive control theory made possible the application of adaptive controllers for the control of uncertain non linear systems.…”