Formation of Bifurcated Wakes Behind Finite Span Flapping Wings
23 Jul 2013-AIAA Journal (American Institute of Aeronautics and Astronautics)-Vol. 51, Iss: 8, pp 2040-2044
TL;DR: In this article, the Strouhal number was used to measure the angle of the airfoil and initial pitch angle, respectively, for a single wing with a single chord.
Abstract: Nomenclature C = chord length, m C T = thrust coefficient f = flapping frequency, Hz h tip = plunge amplitude at the wing tip, m k = ωC∕U ∞ , reduced frequency l span = wingspan, m Re = U ∞ C∕ν, Reynolds number r z = z-directional distance away from the wing tip, m S wing = wing area, m 2 St = fh tip ∕U ∞ , Strouhal number U ∞ = freestream velocity, m∕s ν = kinematic viscosity of fluid, m 2 ∕s α, α 0 = pitch angle of the airfoil and initial pitch angle, respectively, deg ϕ, ϕ 0 = phase angle and initial phase angle, respectively, rad ω = angular frequency, rad∕s ω z = spanwise (z direction) vorticity
Citations
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01 Jan 2002
TL;DR: In this article, the three-dimensional structure of the flow behind a heaving and pitching finite-span wing is investigated using dye flow visualization at a Reynolds number of 164, which is a variation of the Strouhal number, pitch amplitude and heave/pitch phase angle.
Abstract: The three-dimensional structure of the flow behind a heaving and pitching finite-span wing is investigated using dye flow visualization at a Reynolds number of 164. Phase-locked image sequences, which are obtained from two orthogonal views, are combined to create a set of composite images that give an overall sense of the three-dimensional structure of the flow. A model of the vortex system behind the wing is constructed from the image sequences. Variations of the Strouhal number, pitch amplitude and heave/pitch phase angle are qualitatively shown to affect the structure of the wake.
179 citations
01 Jan 2007
63 citations
TL;DR: In this paper, a model for biologically inspired dynamic morphing wings is proposed and numerical simulations of the low-Reynolds number flows around the flapping morphing wing are conducted in a parametric space by using the immersed boundary method.
Abstract: Dynamically stretching and retracting wingspan has been widely observed in the flight of birds and bats, and its effects on the aerodynamic performance particularly lift generation are intriguing. The rectangular flat-plate flapping wing with a sinusoidally stretching and retracting wingspan is proposed as a simple model for biologically inspired dynamic morphing wings. Numerical simulations of the low-Reynolds-number flows around the flapping morphing wing are conducted in a parametric space by using the immersed boundary method. It is found that the instantaneous and time-averaged lift coefficients of the wing can be significantly enhanced by dynamically changing wingspan in a flapping cycle. The lift enhancement is caused by both changing the lifting surface area and manipulating the flow structures responsible to the vortex lift generation. The physical mechanisms behind the lift enhancement are explored by examining the three-dimensional flow structures around the flapping wing.
42 citations
TL;DR: In this paper, the simple lift decomposition of a flat plate and a rectangular wing at low-Reynolds-number flows is compared with the general force decomposition based on the fully resolved two-and three-dimensional unsteady velocity fields and the planar velocity fields at several spanwise locations in simulated particle-image-velocimetry measurements.
Abstract: Different lift decompositions into the elemental terms are compared based on direct numerical simulations of a flapping flat plate and a flapping rectangular wing at low-Reynolds-number flows. The simple lift formula is given as a useful approximate form that has the vortex force and local acceleration terms. The accuracy of the simple lift formula in lift estimation is quantitatively evaluated in comparison with the general force formulas based on the fully resolved two- and three-dimensional unsteady velocity fields and the planar velocity fields at several spanwise locations in simulated particle-image-velocimetry measurements. In addition, the mathematical connections between the different force formulas are discussed.
20 citations
TL;DR: In this article, the evolution of vortex structures over flapping NACA0012 foils in shear flows and the corresponding aerodynamic performance are numerically studied using a two dimensional (2D) high-order accurate spectral difference Navier-Stokes flow solver, and further analyzed using the dynamic mode decomposition (DMD) method and vortex theory.
15 citations
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TL;DR: In this article, a review of the recent progress in flapping wing aerodynamics and aeroelasticity is presented, where it is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation.
877 citations
"Formation of Bifurcated Wakes Behin..." refers background in this paper
...…= chord length, m CT = thrust coefficient f = flapping frequency, Hz htip = plunge amplitude at the wing tip, m k = ωC∕U∞, reduced frequency lspan = wingspan, m Re = U∞C∕ν, Reynolds number rz = z-directional distance away from the wing tip, m Swing = wing area, m 2 St = fhtip∕U∞,…...
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