Flutter Suppression Of High-Aspect-Ratio Wings With Synthetic Jet Actuators

The flutter suppression of wings is a hot topic in the field of aeroelasticity. Especially because of the features of light weight and high flexibility, the flutter of high-aspect-ratio aircraft wings is a challenging problem. Although both traditional methods of passive and active flutter suppression can effectively avoid the flutter, the former has to pay the cost of the inherent advantage of high-aspect-ratio aircraft wings, i.e., passive flutter suppression reduces the lift-drag ratio, and the latter has the disadvantages such as the difficulty of obtaining all model parameters and the time lag between the response of actuators and control commands. Synthetic jet technology, one kind of active flow control proposed in the recent twenty years, has been attracting a great attention of scholars all over the world and shown bright prospect in applications. However, researches on flutter suppression of wings based on synthetic jet technology have been still rare at present.By exploiting the flow features of synthetic jets, flutter suppression methods were proposed for classic flutter and stall flutter in this dissertation. The effects of the above methods were numerically verified by taking the NACA0012airfoil as a case study. The following studies were carried out in this dissertation:(1)The critical flutter speed and flutter amplitude under nonlinear aerodynamic load were analyzed for a two-dimensional airfoil model. The feedback control law designed for classic flutter suppression with synthetic jets was also developed. The control law can be briefly stated as follows:apply synthetic jets when negative work is done on the wings by the aerodynamic force so that energy consumption could be enlarged. The feasibility of the control law was tested and verified by the case of NACA0012airfoil.(2)The high-aspect-ratio aircraft wing was simplified as a thin-walled closed sections composite cantilever beam model. Based on a two-degree-of-freedom model including the vertical bending and torsion motions, a three-dimensional airfoil model was derived, in which the aerodynamic force was decomposed into quasi-steady and fluctuating aerodynamic force indicating vortex shedding. Bias symmetry laminates were adopted as the layers of composite wings. The validation work was carried out by comparing with the results from the FEM software ABAQUS.(3)The aeroelastic tailoring was analyzed for the three-dimensional wing model of NACA0012airfoil. The influence of ply angles on the critical flutter speed, flutter frequency, static deflection and dominant frequency of free vibration was also investigated. The frequency response analysis under stall state was carried out. To reduce the amplitude of forced vibration, we took the advantage that synthetic jets could change the frequency and phase of vortex shedding along the spanwise direction. Two methods for stall flutter suppression using synthetic jets (frequency control method and phase control method) were put forward. The above two methods could work without using complex control law and precise control system, thus being simple and practicable. Under particular control parameters, the amplitude of torsion vibration would drop to36.47%of the original one as for the first method, and the second one would reduce the resonant amplitude of the first bend mode99.42%and that of the first torsion mode98.83%, respectively.