11 - Airload–Structure Interactions and Aero–Elastic Effects

Summary

Aero-elasticity is concerned with the interaction of air flow with flexible structures. The load-carrying structures are designed to sustain the loads encountered during operation, but the wings will bend and twist under the airloads – the pressure forces acting over the surface of the vehicle. Depending on structural and flow characteristics, this leads to static (wing divergence, control reversal) and dynamic (flutter) effects that limit the airspeed. This chapter shows how the wing shape can be determined for a given flight condition. Computational fluid dynamics (CFD) delivers the airloads and a structural model provides the resulting deformations in the iterative process of the aero-elastic loop to find the deformation to the flight shape. The structural model is a finite-element discretization of a simple beam approximation of the real structure, and the transfer of forces from CFD and of deformations from the finite-element model is explained. The software is a loosely coupled, modular framework that illustrates the required data exchange. The loop is exemplified by low-speed static aero-elastic analyses of wing deformation, divergence, and control reversal in two case studies: a wing model in a wind tunnel undergoing divergence and control reversal; and the determination of the flight shape of a unmanned aerial vehicle in pull-up and push-down maneuvers.​