Applications of the unsteady vortex-lattice method in aircraft aeroelasticity and flight dynamics

An evaluation of computational models is carried out for flight dynamics simulations on low-speed aircraft with very-flexible high-aspect ratio wings. Structural dynamic models include displacement-based, strain-based, and intrinsic (first-order) geometrically-nonlinear composite beams, while thin-strip and vortex lattice methods are considered for the unsteady aerodynamics. It is first shown that all different beam finite element models (previously derived in the literature from different assumptions) can be consistently obtained from a single set of equations. This approach has been used to expand existing strain-based models to include shear effects. Comparisons are made in terms of numerical efficiency and simplicity of integration in flexible aircraft flight dynamics studies. On the structural modeling, it was found that intrinsic solutions can be several times faster than conventional ones for aircraft-type geometries. For the aerodynamic modeling, thin-strip models based on indicial airfoil response are found to perform well in situations dominated by small amplitude dynamics around large quasi-static wing deflections, while large-amplitude wing dynamics require three-dimensional descriptions (e.g. vortex lattice).

Structural and Aerodynamic Models in Nonlinear Flight Dynamics of Very Flexible Aircraft

A review on non-linear aeroelasticity of high aspect-ratio wings

This paper reviews the applicability of some conventional structural design practices to the analysis and design of very flexible aircraft. The effect of large structural deformations and the coupling between aeroelasticity and flight dynamics is investigated in different aspects of the aircraft structural design process, including aeroelastic stability, loads, and flight dynamics and control. This is illustrated with a numerical example of the static and dynamic responses of a representative high-altitude long-endurance vehicle. Suggestions are presented for the development of appropriate frameworks to design and analyze very flexible aircraft.

/pdf/reexamined-structural-design-procedures-for-very-flexible-25jtokebwu.pdf

Reexamined Structural Design Procedures for Very Flexible Aircraft

This paper investigates the model reduction, using balanced realizations, of the unsteady aerodynamics of maneuvering flexible aircraft. The aeroelastic response of the vehicle, which may be subject to large wing deformations at trimmed flight, is captured by coupling a displacement-based flexible-body dynamics formulation with an aerodynamic model based on the unsteady vortex lattice method. Consistent linearization of the aeroelastic problem allows the projection of the structural degrees of freedom on a few vibration modes of the unconstrained vehicle but preserves all couplings between the rigid and elastic motions and permits the vehicle flight dynamics to have arbitrarily large angular velocities. The high-order aerodynamic system, which defines the mapping between the small number of generalized coordinates and unsteady aerodynamic loads, is then reduced using the balanced truncation method. Numerical studies on a representative high-altitude, long-endurance aircraft show a very substantial reducti...

https://spiral.imperial.ac.uk/bitstream/10044/1/11566/4/Hesse%202013.%20Reduced-Order%20Aeroelastic%20Models%20for%20the%20Dynamics%20of%20Manoeuvring%20Flexible%20Aircraft.pdf

Reduced-Order Aeroelastic Models for Dynamics of Maneuvering Flexible Aircraft

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 HALE-wing 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.

P. C. Chen

Papers

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