Nonlinear-Aerodynamics/Nonlinear-Structure Interaction Methodology for a High-Altitude Long-Endurance Wing

Abstract

Nonlinear aeroelastic analysis is essential for high-altitude long-endurance (HALE) aircraft. In the current paper, we have presented a computational aeroelastic tool for nonlinear-aerodynamics/nonlinear-structure interaction. Specifically, a consistent nonlinear time-domain aeroelastic methodology has been integrated via tightly coupling a geometrically exact nonlinear intrinsic beam model and the generalized unsteady vortex-lattice aerodynamic model with vortex roll-up and free wake. The effects of discrete gust as well as flow separation at various angles of attack from attached flow to the stall and poststall ranges are also included in the nonlinear aerodynamic model. A HALEwing model is analyzed as a numerical example. The trim angle of attack is first found for the wing, and the results show that aeroelastic instability could occur at higher angles of attack. The HALE-wing model under the trim condition is then analyzed for various gust profiles to which it is subject. It is found that for certain gust levels, the elastic deformations of the HALE wing tend to become unstable: notably, the in-plane deflections become very significant. It is noted for the unstable solution of the HALE wing that the flow may be well beyond the stall range. An engineering approach with the use of the nonlinear sectional lift is attempted to consider such stall effects.

Robust Aeroelastic Control of Very Flexible Wings using Intrinsic Models

“…Instead they observed that in general stall and other nonlinear aerodynamic effects will set in well before significant structural nonlinearity is observed. 27 Intrinsic / UVLM 164 -Murua et al 28 Displacement / UVLM 165 69 Table 3: Flutter velocity and frequency for the Goland wing at ρ ∞ = 1.02 kg m −3…”

“…While the resulting set is not orthogonal, it was found to simplify the numerical solution of the nonlinear system. Upon projecting onto modal coordinates using (8), (1) becomes…”

“…3 A number of integrated simulation frameworks have been constructed to model the nonlinear response to gust loads of very flexible aircraft. [4][5][6][7][8][9] They have provided substantial evidence of the importance of modelling large, geometrically-nonlinear deflections, and the challenges associated to the development of control systems for gust alleviation and trajectory tracking in such systems. Cook et al 10 and Dillsaver et al 11 applied H ∞ and LQG controllers respectively to full aircraft models and investigated the response to gust and continuous disturbances.…”

Integrated Flight Dynamics and Aeroelasticity of Flexible Aircraft with Application to Swept Flying Wings

“…A first-order, explicit time-stepping scheme is employed. 4,17,18 This results in a time-varying, discrete-time system of equations, written for time step k + 1, of the form…”

“…This has forced engineers to develop multi-disciplinary computational tools for early-stage and control system design that can predict the interaction of aircraft elastic response, rigid-body motion, and aerodynamic forcing. 1,2,3,4,5,6 In addition to this, several flight test programs 7,8 have been developed recently that specifically target the phenomenon of aeroelastic/rigid-body coupling with the intention of developing active aeroelastic control systems for stability augmentation and disturbance rejection. Most saliently, the intended handover of the Lockheed-developed X-56 Multi-Utility Technology Testbed (MUTT) to NASA has created a focal point for public domain research into flexible aircraft flight dynamics (FAFD) and control.…”