Resumen de Fluid-structure interaction with the application to the non-linear aeroelastic phenomena
The complex environmental situation and the legal requirements for decreasing pollutant emissions and fuel consumption have increased the interest in reducing the empty weight and drag of vehicles and developing renewable energy sources. Due to the former, the aviation industry has proposed new designs integrating high strength-to-weight ratios, such as composite materials and higher aspect ratio wings. These increases in aspect ratio have also been applied to wind energy generation. The rotors of wind turbines are increasing their diameters in recent years: a clear example is the massive off-shore facilities. Using larger and lightweight structures increases the effects of the aerodynamic loads on structural deformation. Structural dynamics are strongly connected to the air-structure interaction. This phenomenon, called aeroelasticity, combines the effect of the external aerodynamic loads, the inertial forces, and the internal elastic stress of the structure. The complex combination of all the previous effects may damp the vibrations of the structure, or on the contrary, they could increase their amplitude, resulting in an unstable phenomenon.
The simulation of the aeroelastic phenomena can be performed using different approaches. The well-known finite element analysis is the most extended methodology for solving solid elastic equations. Regarding fluid conservation equations, computational fluid dynamics is the principal tool for resolving general aerodynamic problems. The aeroelastic simulations can be calculated by combining the previous algorithms. Nevertheless, the computational cost of these methodologies is excessive for a general engineering case. Therefore, new methodologies are required.
This work focuses on developing aeroelastic reduced-order models that compute the coupled phenomena without substantial accuracy losses. Initially, the complete three-dimensional structure is reduced to an equivalent section that reproduces the structure. The equivalent structural section is coupled with two aerodynamic models. The first one uses the forces calculated with aeroelastic computational fluid dynamics. Then, a surrogate model based on artificial neural networks is combined with the equivalent section. Both models show accurate agreement compared to the complete three-dimensional simulations in predicting unstable velocity. However, the three-dimensional aerodynamic effects, load distribution, orthotropic materials, and structural couplings cannot be considered.
In order to solve the previous limitations, a reduced-order model based on a beam element solver is proposed. The algorithm is designed to consider a general orthotropic material and different typologies of aeroelastic problems. Initially, the software is proven to simulate accurately a squared cross-section composite material beam. The results are validated with the complete three-dimensional simulations, demonstrating the capabilities of the tool for predicting the instabilities and the effects of the fiber orientations. Then, the algorithm is used for simulating a wind turbine blade, and the algorithm results are used to improve the operation range of the blades without weight penalties. Finally, a resistant membrane wing is simulated, obtaining high accuracy in the prediction of the flutter velocity compared with the complete coupled simulation. In addition, the only limitation of the model is the prediction of the membrane distortion.
The work presents a set of reduced-order models that allow for reducing the computational cost of the aeroelastic simulations by orders of magnitude. In addition, a decision pattern is provided for selecting the appropriate algorithm for the interest problem.
