Aerodynamic theory for membranes and sails

Newman, B. G.

doi:10.1016/0376-0421(88)90008-5

Cited by 17 publications

(24 citation statements)

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“…Lowering the angle further, a hysteresis would occur, schematically shown in FigA. Thus, the sail shape becomes unstable and the deformations exceed the validity of the method, which cannot yet handle luffing that occurs earlier at higher excess lengths [13]. However, the algorithm gives stable solutions for negative incidence.…”

Section: Resultsmentioning

confidence: 93%

Turbulent Two-Dimensional Flow Around a Flexible Membrane Airfoil

Bunge

Rung

Thiele

2002

New Results in Numerical and Experimental Fluid Mechanics III

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SummaryThe two-dimensional, incompressible f10w at Reynolds number Re = Uc;; ·e = 1.3.10 6 around an inextensible, flexible membrane airfoil (sail) with varying excess length E is examined sol ving the Reynolds-Averaged Navier-Stokes (RANS) equations on grids deforming according to the sail movement within fixed outer boundaries. Results are presented for fully turbulent conditions employing closure models of different degree of complexity in comparison to experimental and analytical results. Good agreement can be found for low angle of attack. However, for higher angle of attack, approaching onset of separation and beyond, the predictive accuracy varies significantly with the representation of turbulence in the presence af strong unsteady phenomena.

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Section: Resultsmentioning

confidence: 93%

Turbulent Two-Dimensional Flow Around a Flexible Membrane Airfoil

Bunge

Rung

Thiele

2002

New Results in Numerical and Experimental Fluid Mechanics III

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“…Secondly, theoretical and experimental work on sail profiles (Thwaites, 1961;Nielsen, 1963;Greenhalgh et al, 1984;Newman and Low, 1984;Newman, 1987;Sugimoto and Sato, 1991) has shown that, owing to the mutual interdependence of shape and aerodynamic loading, multiple profile shapes are simultaneously possible at low angles of attack, a phenomenon that can cause serious instabilities (Fig.·2). At high angles of attack only a simple convex shape is possible (Fig.·2, shape 1); as incidence is reduced, the only significant effect at first is a rearward migration of the chordwise position of maximum camber.…”

Section: Introductionmentioning

confidence: 99%

“…If the angle of attack is reduced below ideal incidence, a point of inflexion appears at the leading edge that migrates rearward as the angle of attack is reduced (Fig.·2, shape 3). While the sail is in this state it becomes susceptible to a frequently severe fluttering instability called luffing (Greenhalgh et al, 1984;Newman and Low, 1984;Newman, 1987;Sugimoto and Sato, 1991). The lift is still positive at this stage, but if incidence is reduced still further, a point is eventually reached when an S-shaped profile is no longer tenable, and the sail 'pops through', adopting an entirely convex shape, but lying beneath the chord line (Fig.·2, shape 4).…”

Section: Introductionmentioning

confidence: 99%

“…Unsurprisingly, the lift is now negative. This pop-through generally occurs at a small negative angle of attack, the precise value depending on camber and the extent of flow separation (Greenhalgh et al, 1984;Newman, 1987). If the angle of attack of the upside-down sail is now increased, the profile will not cross the chord line again instantly, but must once again pass through ideal incidence and an S-shaped phase (Fig.·2, shape 5) before it pops through and attains positive camber once more.…”

Section: Introductionmentioning

confidence: 99%

“…If the angle of attack of the upside-down sail is now increased, the profile will not cross the chord line again instantly, but must once again pass through ideal incidence and an S-shaped phase (Fig.·2, shape 5) before it pops through and attains positive camber once more. In other words, sail profiles exhibit hysteresis behaviour around ideal incidence (Greenhalgh et al, 1984;Newman, 1987;Sugimoto and Sato, 1991).…”

Section: Introductionmentioning

confidence: 99%

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Sailing the skies: the improbable aeronautical success of the pterosaurs

Wilkinson

2007

Journal of Experimental Biology

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SUMMARY Pterosaur wings bore a striking resemblance to sails, having a bony spar at the leading edge, formed by the forelimb and one enormously elongated digit,and an elastic wing membrane. Such simple wings would be expected to have performed badly due to excessive deformation, membrane flutter and poor control characteristics. Here I discuss how certain anatomical features,specifically a forewing membrane in the inner part of the wing and a system of fibres embedded in the distal part, may have countered these shortcomings. The forewing, supported by the unique pteroid bone, would have reduced the wings'geometric twist, and has been shown in wind tunnel tests to improve membrane stability at low angles of attack and dramatically increase the maximum lift coefficient at high angles of attack. The function of the fibres is poorly understood, but it is suggested that they improved membrane stability and optimised twist nearer the wingtips.

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Numerical simulation of viscous flow interaction with an elastic membrane

Matthews

Greaves

Williams

2007

Numerical Methods in Fluids

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SUMMARYA numerical fluid-structure interaction model is developed for the analysis of viscous flow over elastic membrane structures. The Navier-Stokes equations are discretized on a moving body-fitted unstructured triangular grid using the finite volume method, taking into account grid non-orthogonality, and implementing the SIMPLE algorithm for pressure solution, power law implicit differencing and Rhie-Chow explicit mass flux interpolations. The membrane is discretized as a set of links that coincide with a subset of the fluid mesh edges. A new model is introduced to distribute local and global elastic effects to aid stability of the structure model and damping effects are also included. A pseudo-structural approach using a balance of mesh edge spring tensions and cell internal pressures controls the motion of fluid mesh nodes based on the displacements of the membrane.Following initial validation, the model is applied to the case of a two-dimensional membrane pinned at both ends at an angle of attack of 4 • to the oncoming flow, at a Reynolds number based on the chord length of 4×10 3 . A series of tests on membranes of different elastic stiffness investigates their unsteady movements over time. The membranes of higher elastic stiffness adopt a stable equilibrium shape, while the membrane of lowest elastic stiffness demonstrates unstable interactions between its inflated shape and the resulting unsteady wake. These unstable effects are shown to be significantly magnified by the flexible nature of the membrane compared with a rigid surface of the same average shape.

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Aerodynamic theory for membranes and sails

Cited by 17 publications

References 0 publications

Turbulent Two-Dimensional Flow Around a Flexible Membrane Airfoil

Turbulent Two-Dimensional Flow Around a Flexible Membrane Airfoil

Sailing the skies: the improbable aeronautical success of the pterosaurs

Numerical simulation of viscous flow interaction with an elastic membrane

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