Flutter de seções típicas com folga

Abstract

The science interested in the interaction between the deformation of an elastic structure in an airflow and the aerodynamics forces is called Aeroelasticity. Many problems in Aeroelasticity are naturally nonlinear and, for that reason, its behavior is not described very well with the linear analysis. Thus, new tools are necessary to predict and study the nonlinear aeroelasticy with the purpose to reduce the flying risks and enhance the aircraft efficiency. Recently, studies in 3-DOF airfoils with control surfaces are using certain nonlinearities to characterize the effects on its dynamics system. These methods consider on implementing the freeplay on control surfaces or other types of joints. This sort of problem is relevant because it can lead to unlikeable performance, reducing significantly the fly envelope, heading to structural failures, material fatigue and adverse aircraft responses. Therefore, it is essential to identify the structural dynamics effects induced by the nonlinearity freeplay on the control surface. Due to aerodynamics forces and momentums acting together on the airfoil section is fundamental to do a nonstationary aerodynamics analysis, on which will be based in angles of attack smaller than 20 and with values smaller than 0.1 of reduced frequencies. Furthermore, a dynamic analysis for the airfoil section with control surface is done using the Lagrange equations to figure the equations of motion. The nonlinearity enters in the dynamic system by a curve fitting utilizing a hyperbolic function approximation coming to a third-degree polynomial. This function would be added to the DOF related to control surface in the stiffness matrix. As the entire system was build and characterized, it is possible to find the effects on the system with freeplay. For instance, a subsonic airstream is conducted to a several computational simulations with the main goal is to characterize the more relevant differences between the aeroelastic system with and without the freeplay. Finally, the results observed is larger amplitudes on DOF responses for the system with freeplay and the appearance of the limit cycle oscillations after the flutter.