Multidisciplinary design optimization of camber-morphing multi-element airfoils
Creators: name: Wright, Cody Alexander
Publisher: name: No Publisher Supplied
Year: 2022

description: Most fixed-wing aircraft, from model- to large cargo-scale, employ wings with multiple discontinuous segments in order to control the aircraft and/or change the wing into a more aerodynamically advantageous shape based on the flight phase. By the nature of discontinuous surfaces, aerodynamic losses can occur due to flow separation induced by interfaces. In addition, conventional actuation systems for such surfaces are mechanically very complex. In this research, it is proposed that conventional control surfaces on wings can be replaced with morphing control-surfaces with surface-bonded, so-called strain-inducing, actuators, particularly with piezocomposite devices. Such aerodynamic surfaces can help to reduce losses due to interfaces by using a continuous surface. This concept is also referred to as a solid-state airfoil or a wing. Such mechanism-free methods have been demonstrated for small, unmanned aircraft; however, the largest scale for which strain-induced actuation is an effective method for camber morphing is unknown. The primary goal of this dissertation is to understand and expand the concept of camber morphing with induced-strain actuators, particularly piezocomposites, by exploring their capabilities at the scale of a commercial passenger aircraft. Since it is well known that actuator effectiveness decreases with increasing size of the structure being morphed, it is also of interest to predict the performance of a system with a future “vision” actuator that is not available today; however, may become available in the future with advancement of smart materials. These goals are accomplished with the completion of three primary tasks: 1) Extension of a static fluid-structure interaction analysis and design optimization framework for surface-actuated continuous airfoils. 2) Validation of said framework through experimental testing of a prototype, fabricated using parameters based on the design optimization results. 3) Determination of the efficacy of piezocomposite actuation at the scale of a commercial passenger aircraft using the validated framework. First, a conceptual design of the airfoil is developed, defining the design space. The airfoil design has a single piezocomposite actuator element on the top surface, and up to two actuator elements on the bottom surface: allowing asymmetry of actuated airfoil geometries. The position of the actuator elements can vary on the surface as well as substrate thickness beneath the actuator elements. The proposed airfoil can also vary substrate material properties and substrate thickness of the non-actuated portions of the surface. Finally, a fixed boundary region is established on the geometry to represent the ribs, spar and other internal load-carrying structures. A deformation and stress solution of the candidate airfoil is found using static aeroelastic assumptions. Using a genetic algorithm optimization method for examining different candidate airfoil designs, various so-called optimal designs are found for a list of common objective functions. Once an optimal design is produced, a parametric analysis is performed on the airfoil, examining its aerodynamic properties over its operational range. The most promising airfoil designs are fabricated into model-sized prototypes, where they are benchtop and wind-tunnel tested. The prototypes are fabricated by layering a composite laminate around an airfoil mold. The piezocomposite actuators are then bonded onto the composite laminate structure. Deformation of the prototype airfoils, under a static excitation, is measured and compared to the predicted deformation of the finite element model. The comparison shows near excellent agreement. Subsequently, the aerodynamic forces measured in the wind tunnel are compared to those obtained by the fluid-structure interaction methodology. This comparison shows good agreement with acceptable errors explained by known differences between the fluid solvers and the wind tunnel setup. Using the validated model, design optimization studies are conducted for a full-scale airfoil. The full-scale optimization results provide a landscape for describing the trade-off of actuation authority and compliance. Furthermore, camber-morphing is performed on an airfoil for a commercial passenger aircraft using a future “vision” actuator. This exploration examines potential airfoil capabilities as the strain-induced actuator technologies are likely to mature along with developments in smart materials.