Explicit Role of Viscosity in Generating Lift

Liu, Tianshu; Wang, Shizhao; He, Guowei

doi:10.2514/1.j055907

Cited by 19 publications

(15 citation statements)

References 14 publications

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“…The C l -curve predicted by Eq. (12a) exhibits the non-linear behavior that is consistent with the CFD results at Re c = 200 [20] and measurement data of an aluminum (Al) foil wing with the aspect ratio of 6 at Re c = 7500 [33]. In contrast, thin-airfoil theory gives the linear C lcurve with the larger lift slope.…”

Section: Viscous-flow Lift Formulasupporting

confidence: 76%

“…5 The chordwise distributions of the surface pressure coefficient difference across the flat plate at different AoAs. From Liu et al [20] satisfied at the trailing edge. Nevertheless, the Taylor-Sears condition that the net vorticity flux is zero at the trailing edge holds in this viscous flow, which is a generalized form of the Kutta condition (see Section 6).…”

Section: Viscous-flow Lift Formulamentioning

confidence: 94%

“…Lift of a flat-plate airfoil can be directly evaluated as a viscous-flow result without explicitly using the circulation and K-J theorem in classical aerodynamics [20]. This nontraditional attempt is based on the intrinsic relationship between the skin friction topology and surface pressure structure in a viscous flow.…”

Section: Viscous-flow Lift Formulamentioning

confidence: 99%

“…This nontraditional attempt is based on the intrinsic relationship between the skin friction topology and surface pressure structure in a viscous flow. For an incompressible viscous flow over a stationary curved surface, an exact relation between the surface pressure gradient ∇p and the skin-friction vector τ can be derived from the NS equations [20,28,29,30,31]. In particular, for a flat surface where the curvature effect vanishes, this on-wall relation is written as…”

Section: Viscous-flow Lift Formulamentioning

confidence: 99%

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Evolutionary understanding of airfoil lift

Liu

2021

Adv. Aerodyn.

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This review attempts to elucidate the physical origin of aerodynamic lift of an airfoil using simple formulations and notations, particularly focusing on the critical effect of the fluid viscosity. The evolutionary development of the lift problem of a flat-plate airfoil is reviewed as a canonical case from the classical inviscid circulation theory to the viscous-flow model. In particular, the physical aspects of the analytical expressions for the lift coefficient of the plate-plate airfoil are discussed, including Newton’s sine-squared law, Rayleigh’s lift formula, thin-airfoil theory and viscous-flow lift formula. The vortex-force theory is described to provide a solid foundation for consistent treatment of lift, form drag, Kutta condition, and downwash. The formation of the circulation and generation of lift are discussed based on numerical simulations of a viscous starting flow over an airfoil, and the evolution of the flow topology near the trailing edge is well correlated with the realization of the Kutta condition. The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.

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Section: Viscous-flow Lift Formulasupporting

confidence: 76%

Section: Viscous-flow Lift Formulamentioning

confidence: 94%

Section: Viscous-flow Lift Formulamentioning

confidence: 99%

Section: Viscous-flow Lift Formulamentioning

confidence: 99%

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Evolutionary understanding of airfoil lift

Liu

2021

Adv. Aerodyn.

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“…As a consequence numerical agreement for changes in the lift-slope (with reference to 2 • π) were not convincing. Liu et al [23] investigates the influence of viscosity to the generation of lift at small RN (=200). Her findings indicate that a nonlinear c L (α) curve should be more approprate in contrast to a linear one from Yates' model but with modified slope only [24].…”

Section: Viscous Thin Airfoil Theory I: Rn <<mentioning

confidence: 99%

An Explanation and Understanding of Aerodynamic Lift by Triple Deck Theory

Schaffarczyk¹

2021

Preprint

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An explanation of aerodynamic lift still is under controversial discussion as can be seen, for example, in a recent published article in Scientific American [1]. In contrast to an approach via integral conservation laws we here review an approach via the classical Kutta-Condition and its relation to boundary layer theory. Thereby we summarize known results for viscous correction to the lift coefficient for thin aerodynamic profiles and try to remember the work on triple-deck or higher order Boundary Layer theory, its connection to interactive boundary layer theory, viscous/inviscid coupling as implemented to well-known engineering code Xfoil. Finally we compare its findings to simple 2D numerical solution of full Navier Stokes equations (CFD)models. As a conclusion, a clearer definition of terms like understanding and explanation applied to the phenomenon of aerodynamic lift will be given.

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Birth of starting vortex and establishment of Kutta condition

Salazar,

Liu

2025

European Journal of Mechanics - B/Fluids

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Explicit Role of Viscosity in Generating Lift

Cited by 19 publications

References 14 publications

Evolutionary understanding of airfoil lift

Evolutionary understanding of airfoil lift

An Explanation and Understanding of Aerodynamic Lift by Triple Deck Theory

Birth of starting vortex and establishment of Kutta condition

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