Near field of the tip vortex behind an oscillating rectangular wing

Ramaprian, B. R.; Zheng, Youxin

doi:10.2514/3.13961

Cited by 4 publications

(5 citation statements)

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“…It is believed that the various observed unsteady boundary-layer and stall events will also have a direct influence on the flow structure of the tip vortex thus generated. So far, only three experimental investigations (Freymuth, Finaish & Bank 1985;Ramaprian & Zheng 1998;Chang & Park 2000), to the author's knowledge, with a limited frequency and amplitude range, have been reported in the literature.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the near-field tip vortex behind an oscillating wing

Birch

Lee

2005

J. Fluid Mech.

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The near-field tip-vortex flow structure behind an oscillating NACA 0015 wing was investigated at ${\hbox {{\it Re}}}\,{=}\,1.86 \times 10^{5}$. For attached-flow and light-stall oscillations, a small hysteretic property existed between the pitch-up and pitch-down motion, and many of the vortex flow features were found to be qualitatively similar to those of a static wing. For deep-stall oscillations, the wing oscillations imposed a strong discrepancy in contour shapes and magnitudes between the pitch-up and pitch-down phases of the oscillation cycle. The vortex was less organized during pitch-down (as a result of leading-edge-vortex-induced massive flow separation) than during pitch-up. The tangential velocity, circulation and lift-induced drag increased progressively with the airfoil incidence, and had higher magnitudes during pitch-up than during pitch-down, while varying slightly with the downstream distance. The vortex size, however, was larger during pitch-down than during pitch-up. The axial flow was always wake-like during the deep-stall oscillation cycle. The normalized circulation within the inner region of the tip vortex also exhibited a self-similar structure, similar to that of a static wing, and was insensitive to the reduced frequency.

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Section: Introductionmentioning

confidence: 99%

Investigation of the near-field tip vortex behind an oscillating wing

Birch

Lee

2005

J. Fluid Mech.

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“…Good agreement is achieved with (1.1) and (1.2) over a wide range of Reynolds numbers and boundary conditions (see Birch et al 2004), including cases of highly unsteady vortices (Ramaprian & Zheng 1998;Birch & Lee 2005) and those subjected to intense free-stream turbulence (Beninati & Marshall 2005;Bailey & Tavoularis 2008). However, all vortices generated within experimental flow facilities are acknowledged to be subject to a low-amplitude, random 'wandering'; this phenomenon results in a Gaussian distribution of the locus of vortex centres in both time and space.…”

Section: Introductionmentioning

confidence: 64%

Boundary conditions and vortex wandering

2014

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A direct numerical simulation of a Batchelor vortex has been carried out in the presence of freely-decaying turbulence, using both periodic and symmetric boundary conditions; the latter most closely approximates typical experimental conditions, while the former is often used in computational simulations for the purposes of numerical convenience. The higher-order velocity statistics were shown to be strongly dependent upon the boundary conditions, but the dependence could be mostly eliminated by correcting for the random, Gaussian modulation of the vortex trajectory commonly referred to as 'wandering' using a technique often employed in the analysis of experimental data. Once corrected for this wandering, the strong peaks in the Reynolds stresses normally observed at the vortex centre were replaced by smaller local extrema located within the core region but away from the centre. The distributions of the corrected Reynolds stresses suggested that the formation and organization of secondary structures within the core is the main mechanism in turbulent production during the linear growth phase of vortex development.

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“…4c. However, it is known that in the near field, the rms amplitude of the meandering is generally less than 0:5%c which led to a maximum 5 and 6% vortexmeandering-induced variation in the core radius and the peak tangential velocity [28], respectively, and that the effects of vortex meandering only gains significance in the far field [23]. Additional measurements are needed to quantify the vortex meandering associated with the unsteady-wing experiments.…”

Section: B Effects Of Npmentioning

confidence: 95%

“…The oscillating wing was chosen to simulate the quasiperiodic first harmonic angle-of-attack variations that are found on helicopter rotors during low-speed forward flight [21][22][23]. Special emphases were placed on the determination of the phase-locked ensembleaveraged core vortex flow parameters, obtained by using a miniature triple hot-wire probe, over one cycle of oscillation.…”

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confidence: 99%

Tip Vortex Control via a Tab Deflecting at Higher Harmonic Frequencies

Lee

Pereira

2008

AIAA Journal

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The impact of a trailing-edge tab, actuated at different start times and higher harmonic frequencies, on the size and strength and the position of a tip vortex generated by an oscillating NACA 0015 wing was investigated. The results show that for all the tab control cases tested, the peak tangential velocity of the tip vortex was found to be a weak function of the tab motion, whereas the core radius and circulation were strongly dependent upon the tab deflection. The 2=revolutions higher harmonic tab control actuated during pitch up produced the largest reduction in the peak tangential velocity and the greatest increase in the core radius and also provided the most promising blade-vortexinteraction suppression. Similar control effectiveness was also observed for 3=revolutions higher harmonic tab control motion but to a lesser extent. The 4=revolutions higher harmonic tab control was, however, most effective during the pitch-down flow-reattachment process.span over which 2-D blade-vortex interaction occurs NP = nth harmonic of f o Re = Reynolds number, u o c= r = radial position r c = core radius t = time u = mean axial velocity u o = freestream velocity u 0 = rms velocity fluctuation v = tangential velocity x, y, z = axial, transverse, and span-wise direction = angle of attack m = mean max = maximum min = minimum = vortex strength or circulation c = core circulation o = total circulation = BVI parameter, c c=y c c 2 u o j controlled c c=y c c 2 u o j uncontrolled = deflection amplitude = streamwise vorticity = reduced frequency, f o c=u o = fluid kinematic viscosity o = freestream fluid density = phase angle, !t 2f o t Subscripts d = pitch down u = pitch up

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Near field of the tip vortex behind an oscillating rectangular wing

Cited by 4 publications

References 0 publications

Investigation of the near-field tip vortex behind an oscillating wing

Investigation of the near-field tip vortex behind an oscillating wing

Boundary conditions and vortex wandering

Tip Vortex Control via a Tab Deflecting at Higher Harmonic Frequencies

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