The influence of airfoil kinematics on the formation of leading-edge vortices in bio-inspired flight

Vorticity transport and the leading-edge vortex of a plunging airfoil

“…Buchholz et al (2011) proposed a scaling parameter for the total circulation shed by finite-aspect-ratio pitching panels, based on a simple model of surface pressure gradients. This parameter was shown to collapse the circulation data to an approximately constant value and was consistent with that of Rival et al (2009) to the extent that parameter variation was investigated. DeVoria and Ringuette (2012) found pinchoff and maximum circulation of the vortex structure shed by a rotating trapezoidal fin to also be governed by formation number, but cautioned that spanwise flow in the vortex core can significantly affect the formation process, and defining vortex saturation is often ambiguous due to concurrent breakdown of the vortex.…”

“…Application of this parameter by Rival et al (2009) to the leading-edge vortex circulation of a plunging rigid airfoil at low reduced frequency (k = πfc/U = 0.25) resulted in reasonable collapse in the range 4.4 <T < 5.0, based on maximum vortex circulation. Buchholz et al (2011) proposed a scaling parameter for the total circulation shed by finite-aspect-ratio pitching panels, based on a simple model of surface pressure gradients.…”

Effects of nonuniform incident velocity on a dynamic wind turbine airfoil

“…The surrounding flow and the affected boundary layer influence the vortex generation and pinch off. For the SOS at the angle of attack around 19.7° ↑ , the first LEV generates, but for the COS, this angle varies about 5° on the basis of different Φ. For Φ = 0, the first LEV initiates at 20.7° ↑ and as Φ increases, LEV formation occurs earlier and finally for Φ = π it occurs at 18.1° ↑ .…”

Understanding and controlling vorticity transport in unsteady, separated flows

“…Instead, they found the best way to scale the circulation of the LEV was to use the thickness of the shear layer (Figure 1.4). Alternatively, both Rival et al [93] and Kriegseis et al [61] found the effective shear-layer velocity to be a suitable scaling parameter for the LEV circulation.…”

“…Furthermore, they determined the aerodynamic loads were primarily a function of the angle of attack when the Strouhal number remained low. In their experiments on plunging airfoils, Rival et al [93] used a variety of different plunge motions to demonstrate how altering the plunge velocity so that the maximum angle of attack occurred later in the cycle allowed for the production of stronger LEVs that were located closer to the surface of the airfoil at the end of the downstroke. They went on to hypothesize that adding a pitching motion would help to further delay the detachment of the LEV.…”