Swept wing

Abstract: Vortex breakdown on slender sharp edged and modified delta wings with varying sweep angles investigated in wind tunnel using schlieren system for flow visualization

Abstract: Gliding birds continually change the shape and size of their wings, presumably to exploit the profound effect of wing morphology on aerodynamic performance. That birds should adjust wing sweep to suit glide speed has been predicted qualitatively by analytical glide models, which extrapolated the wing's performance envelope from aerodynamic theory. Here we describe the aerodynamic and structural performance of actual swift wings, as measured in a wind tunnel, and on this basis build a semi-empirical glide model. By measuring inside and outside swifts' behavioural envelope, we show that choosing the most suitable sweep can halve sink speed or triple turning rate. Extended wings are superior for slow glides and turns; swept wings are superior for fast glides and turns. This superiority is due to better aerodynamic performance-with the exception of fast turns. Swept wings are less effective at generating lift while turning at high speeds, but can bear the extreme loads. Finally, our glide model predicts that cost-effective gliding occurs at speeds of 8-10 m s(-1), whereas agility-related figures of merit peak at 15-25 m s(-1). In fact, swifts spend the night ('roost') in flight at 8-10 m s(-1) (ref. 11), thus our model can explain this choice for a resting behaviour. Morphing not only adjusts birds' wing performance to the task at hand, but could also control the flight of future aircraft.

Abstract: The transition behaviour of the boundary layer which is formed along an infinite swept attachment line has been studied experimentally. Circular trip wires and turbulent flat plate boundary layers have been used as sources of disturbance and the range of parameters covered has been such that the results are directly applicable to full scale flight conditions. Simple criteria have been deduced which allow the state of the boundary layer to be determined for given geometric and free stream properties. Sample calculations for typical swept wing configurations suggest that the majority of civil aircraft will have turbulent attachment lines in the cruise and that subsequent relaminarisation in regions of favourable pressure gradient is unlikely.

Abstract: Stewartson Memorial Lecture: Experiments are Telling You Something.- 1. Two- and Three-Dimensional Steady Flows.- 1. Predictions of Airfoil Aerodynamic Performance Degradation Due to Icing.- 2. VISTRAFS: A Simulation Method for Strongly Interacting Viscous Transonic Flow.- 3. Coupling Procedures for Viscous-Inviscid Interaction for Attached and Separated Flows on Swept and Tapered Wings.- 4. New Possibilities of Viscous-Inviscid Numerical Techniques for Solving Viscous Flow Equations with Massive Separation.- 5. Prediction of Post-Stall Flows on Airfoils.- 6. Turbulence Characteristics of Trailing-Edge Flows on Thick and Thin Hydrofoils.- 7. Computational Fluid Dynamics at NASA Ames Research Center.- 8. 3-D Composite Velocity Solutions for Subsonic/Transonic Flows.- 9. Calculation of Transonic Flows for Novel Engine-Airframe Installations.- 10. Calculation of Three-Dimensional Boundary Layers Including Hypersonic Flows.- 11. Supersonic/Hypersonic Euler Flowfield Prediction Method for Aircraft Configurations.- 12. Numerical Simulation of Separated and Vortical Flows on Bodies at Large Angles of Attack.- 2. Two- and Three-Dimensional Unsteady Flows.- 13. The Relevance of Unsteady Aerodynamics for Highly Maneuverable and Agile Aircraft.- 14. Experimental and Computational Studies of Dynamic Stall.- 15. A Critique of the Experimental Aerodynamic Data Base for an Oscillating Straked Wing at High Angles.- 16. On the Effects of Wind Tunnel Turbulence on Steady and Unsteady Airfoil Characteristics.- 3. Stability and Transition.- 17. Applications and Suggested Directions of Transition Research.- 18. Prediction of Transition on Airfoils with Separation Bubbles, Swept Wings, and Bodies of Revolution at Incidence.- 19. Transition in Hypersonic Boundary Layers.- 20. Transition Phenomena on Airfoils Operating at Low Chord Reynolds Numbers in Steady and Unsteady Flow.- 21. Disturbance Growth in an Unstable Three-Dimensional Boundary Layer.- 22. Experiments in Swept-Wing Transition.- 23. Experimental Transition and Boundary-Layer Stability Analysis for a Slotted Swept Laminar Flow Control Airfoil.- 24. Leading-Edge Contamination and Relaminarization on a Swept Wing at Incidence.- References.- Index of Contributors.