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Data on the evolution of the unsteady three-dimensional tip vortex in the near wake (0-3 chordlengths behind the wing) of a rectangular NACA 0015 wing oscillating sinusoidally in pitch about its quarter-chord axis are presented. These data were obtained using three-component laser Doppler velocimetry (LDV). The experiments were performed in a low-speed wind tunnel at a Reynolds number of 1:8 £ £ 10 5 . The wing had a semiaspect ratio of 2. It was oscillated at a frequency of 1 Hz and an amplitude of 5 deg around a mean incidence of 10 deg. The instantaneous LDV data were used to obtain information on the distribution of phase-locked velocity and vorticity components across the vortex, as well as the phase-locked circulation associated with the evolving vortex. The data indicate that the average trajectory of the oscillating vortex in the near eld is very nearly the same as for a stationary wing at the mean incidence. The length and circulation scales, as well as the maximum circulation carried by the vortex ow under the conditions studied, are modulated in a signi cantly nonquasisteady manner. Nevertheless, beyond about 0.7 chordlength, the normalized circulation distribution across most of the inner part of the vortex exhibits, at all times, the same universal behavior as the vortex behind a stationary wing. Nomenclature C L = overall lift coef cient for stationary wing at ® equal to 10 deg c = wing chord f = frequency of oscillation k = reduced frequency, (¼ f c=U 1 ) L = reference length scale, cC L =2 Re = Reynolds number, U 1 c=º r = radial coordinate r 1 = radius at maximum V µ t = time U = phase-locked velocity in the x direction U 1 = freestream velocity V = phase-locked velocity in the inboard .y/ direction V µ = circumferential average of v µ v µ = phase-locked tangential velocity in the vortex W = time-mean velocity in the z direction x = distance along the freestream from the trailing-edge plane x º = distance along the freestream from the leading-edge plane y = spanwise distance measured inboard from the tip y 0 = distance inboard of the vortex center from the tip z = direction normal to the freestream (vertically upward) z 0 = z displacement of vortex center relative to the trailing edge ® = instantaneous angle of incidence 0 = phase-locked circulation around a circle of radius r 0 1 = phase-locked circulation at radius r 1 0 max = circulation associated with vortex 1® = amplitude of oscillation º = kinematic viscosity ! x = axial component of vorticity ! y = spanwise component of vorticity ! z = component of vorticity along the z direction N = time average value ¤ = length normalized by L

9407 0OZ4; BestAvailable Copy REPORT DOCUMENTATION PAGE orme ApNov07e18Put~ mcor?.nq ow'Qen -of this collemtOn of ntohmat-om -% estimated to *,eage I out oer opiforse. ricludingq Ithe . tiowo reviewing instructions. s.arcninq; e.,%t~n data tOcM( 4a6ttcrmiq ard maintaining It.t daia neogeded and connaeelinq and re,ev.cmnq the ýotiemtoni of information Send commentsrqr~t nbsaneI~co n tt.i~tO ~.(o11"t.on at ntormnat,on. .ncic.Jang %.gt~ton*l ?or reduci.ng It"ý urdeft to VVh~nqton raicaduarteri, Service% jS . . SUPPLEMENTARY NOTESThe view, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by oth.L: documentation. Approved for public release; distribution unlimited. ABSTRACT (Maximum 200 words)An experimental study of the tip-vortex behind a NACA 0015 rectangular wing of aspect ratio 4 was carried out to understand the structure and evolution of the vortex in the near-wake region.The results of these experimental studies are presented in this report. These measurements were made nonintrusively using three-component laser-Doppler veloicimetry (LDV). The experiments were carried out at a Reynolds number of about 180,000 in a low-speed wind tunnel. Two cases were studied, namely, (i) stationary wing and (ii) wing oscillating in pitch sinusoidally about its quarter-chord axis. The flow properties measured were the three components of the instantaneous velocity. These data were processed to obtain time-mean and phase-locked flow properties such as velocity, vorticity and turbulence. The data were obtained at several locations at 0.15 -3.0 chord lengths downstream from the trailing edge. The typical distributions of mean velocity, vorticity, circulation and turbulent intensity in the near wake are presented and discussed for the stationary wing. In the case of the oscillating wing, the phase-locked velocity, vorticity and turbulence data show details of the evolution of the unsteady tip vortex downstream from the trailing edge. The results also show that the flow is strongly non-quasi-steady at the oscillation frequency studied. The results are fully archived on tape and are available to any interested reader. These can be used as database in the development of wake models for the finite wing, and in studies of 296-102 GENERAL INSTRUCTIONS FOR COMPLETING SF 26The Report Documentation Page (RDP) is used in announcing and cataloging reports. It is important that this information be consistent with the rest of the report, particularly the cover and title page. ABSTRACTAn experimental study of the tip vortex behind a NACA 0015 rectangular wing of aspect ratio 4 was carried out to understand the structure and evolution of the vortex in the near-wake region. The results of these experimental studies are presented in this report. These measurements were made nonintrusively using three-component laserDoppler velocimetry (LDV). The experiments were carried out at a Reynolds number of ab...