Rollup and Near-Field Behavior of a Tip Vortex

Birch, David M.; Lee, T.; Mokhtarian, Farzin; Kafyeke, F.

doi:10.2514/2.3137

Cited by 34 publications

(24 citation statements)

References 10 publications

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“…The constant total circulation confirms previous observations, where no significant influence of dissipation and flow unsteadiness was found over a range of two to 40 wing chords , and is consistent with results from recent studies of bat wakes . The lack of significant changes in the strength of the separate vortices with increased distance from the animal also shows that the vortex roll-up process was completed by the closest location at which the PIV plane sampled the wake, in agreement with studies of tip vortex development, which showed that rollup is finished approximately 1-1.5 chord lengths behind the wing (Birch and Lee, 2003). Measurements on swept and rectangular wings at Re180,000 have also shown no significant change in circulation between 1 and 3.5 chord length behind the wing (Gerontakos and Lee, 2006).…”

Section: Circulation In the Near And Far Fieldsupporting

confidence: 70%

Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat,Cynopterus brachyotis

Hubel

Riskin

Swartz

et al. 2010

Journal of Experimental Biology

116

114

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SUMMARYWe investigated the detailed kinematics and wake structure of lesser dog-faced fruit bats (Cynopterus brachyotis) flying in a wind tunnel. High speed recordings of the kinematics were conducted to obtain three-dimensional reconstructions of wing movements. Simultaneously, the flow structure in the spanwise plane perpendicular to the flow stream was visualized using time-resolved particle image velocimetry. The flight of four individuals was investigated to reveal patterns in kinematics and wake structure typical for lower and higher speeds. The wake structure identified as typical for both speed categories was a closed-loop ring vortex consisting of the tip vortex and the limited appearance of a counter-rotating vortex near the body, as well as a small distally located vortex system at the end of the upstroke that generated negative lift. We also investigated the degree of consistency within trials and looked at individual variation in flight parameters, and found distinct differences between individuals as well as within individuals. Supplementary material available online at

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Section: Circulation In the Near And Far Fieldsupporting

confidence: 70%

Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat,Cynopterus brachyotis

Hubel

Riskin

Swartz

et al. 2010

Journal of Experimental Biology

116

114

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“…This roll-up process starts at the leading edge and is found to be exceedingly rapid. The vortex flow is observed to become self-similar and axially symmetrical within approximately one to two chord lengths downstream of the trailing edge (Ramaprian and Zheng 1997;Birch et al 2003). However, on rotary wings the spanwise load distribution and the structure of the near wake are substantially different (Mahalingam et al 2000;Komerath et al 2004).…”

Section: List Of Symbolsmentioning

confidence: 89%

Aperiodicity in the near field of full-scale rotor blade tip vortices

et al. 2010

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Blade tip vortices are the dominant vortical structures of the helicopter flow field. The inherent complexity of the vortex dynamics has led to an increasing interest in full-scale in situ experiments, where the near field, closely behind the blade, is of particular interest, since measures of vortex control mostly target this initial stage of development. To examine the near field, threecomponent particle image velocimetry (PIV) measurements of blade tip vortices of a full-scale helicopter in simulated hover flight in ground effect were conducted. A feasible and robust evaluation procedure was developed to minimise the shortcomings of full-scale PIV applications, such as a moderate spatial resolution and an elevated measurement noise level. At vortex ages ranging from w v ¼ 1 to 30°, a pronounced aperiodicity and asymmetry of the vortex were observed in -sections perpendicular to the vortex axes. At w v ¼ 1 , a preferential orientation of the vortex was observed. For increasing wake age, vortex wandering increased while the asymmetry of the vortex cores decreased. The high level of aperiodicity and core asymmetry must be taken into account when considering phase-averaged vortex characteristics in the near wake region. List of symbols

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“…Secondary vortices are formed on the side of the wing and eventually they climb around the corner contributing to the unsteadiness of the primary vortex. PIV measurements on squared tip by Birch et al [8] confirmed the multiple vortices structure in the initial rolling-up of the vortex and they showed both axial velocity deficit and excess in the vortex centre at a distance of 1.5 chords from the trailing edge. Karakus et al [9] concluded that the tip region is dominated by the strong interaction between the multiple secondary vortices and the primary vortex.…”

Section: Introductionmentioning

confidence: 92%

Vortex formation on squared and rounded tip

Giuni

Green

2013

Aerospace Science and Technology

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The vortical flow originated from the tip of a NACA 0012 rectangular wing is described in its initial formation and development over a rounded and a squared tip. Smoke visualizations show the rolling-up kinematic and evolution of the vortical systems moving the plane towards the trailing edge. The presence of intense secondary vortices affects the primary vortex unsteadiness and shape during the formation and in the early wake. Stereoscopic Particle Image Velocimetry is used to describe vorticity, axial velocity and turbulent kinetic energy distributions of the vortex during the formation and in the early wake at different angles of attack of the wing. The rolling-up of the vorticity sheet around the vortex system is strongly influenced by the vortex shape and the intensity of secondary vortices. Turbulence coming from secondary structures and shear layers is wrapped into the roll-up of the vortex and high levels of turbulence are measured in the vortex core. However, a laminar vortex core is observed for the lower angle of attack in the early wake. Comparing the meandering of the vortex for the two wingtip geometries, two different sources of the vortex fluctuation in the wake are identified: the interaction of secondary vortices moving around the primary vortex and the rolling-up of the vorticity sheet. Lastly, measurements in the wake of the wing at zero incidence are also presented showing a distinctive counter rotating vortex pair.

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Rollup and Near-Field Behavior of a Tip Vortex

Cited by 34 publications

References 10 publications

Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat,Cynopterus brachyotis

Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat,Cynopterus brachyotis

Aperiodicity in the near field of full-scale rotor blade tip vortices

Vortex formation on squared and rounded tip

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