No abstract

The coupling of independent structural dynamic and inviscid aerodynamic models, in the time domain, is considered. The accuracy and CPU requirements of the two common approaches, namely ‘weak’ and ‘strong’ coupling procedures, are investigated. It is found that the strong coupling scheme is more accurate than the weak coupling approach, and only for large real time-steps is the strong coupling scheme more expensive. The computational method developed is used to perform transonic aeroelastic and aeroservoelastic calculations in the time domain, and used to compute stability (flutter) boundaries of 2D wing sections. A control law is implemented within the aeroelastic solver to investigate active means of flutter suppression via control surface motion. Comparisons of open and closed loop calculations show that the control law can successfully suppress the flutter and results in a significant increase in the allowable speed index in the transonic regime. The effect of structural nonlinearity, in the form of hinge axis backlash is also investigated. The effect is found to be destabilising, but the control law is shown to still alleviate the destabilising effect.

Transonic flutter and active flap control, in two dimensions, are simulated by coupling independent structural dynamic and inviscid aerodynamic models, in the time domain. A flight control system, to actively control the trailing edge flap motion, has also been incorporated and, since this requires perfect synchronisation of fluid, structure and control signal, the "strong" coupling approach is adopted. The computational method developed is used to perform transonic aeroelastic and aeroservoelastic calculations in the time domain, and used to compute stability ( flutter) boundaries of 2D wing sections. Open and closed loop simulations show that active control can successfully suppress flutter and results in a significant increase in the allowable speed index in the transonic regime. It is also shown that active control is still effective when there is free-play in the control surface hinge. Flowfield analysis is used to investigate the nature of flutter and active control, and the fundamental importance of shock wave motion in the vicinity of the flap is demonstrated.

SUMMARYA computational method to perform transonic aeroelastic and aeroservoelastic calculations in the time domain is presented, and used to predict stability ( utter) boundaries of 2-D wing sections. The aerodynamic model is a cell-centred ÿnite-volume unsteady Euler solver, which uses an e cient implicit time-stepping scheme and structured moving grids. The aerodynamic equations are coupled with the structural equations of motion, which are derived from a typical wing section model. A control law is implemented within the aeroelastic solver to investigate active means of utter suppression via control surface motion. Comparisons of open-and closed-loop calculations show that the control law can successfully suppress the utter and results in an increase of up to 19 per cent in the allowable speed index. The e ect of structural non-linearity, in the form of hinge axis backlash is also investigated. The e ect is found to be strongly destabilizing, but the control law is shown to still alleviate the destabilizing e ect.

No abstract