| Abstract | Wake vortex core profile and stability characteristics have been analysed, based upon enroute flight data, gathered upon research flights using the NRC CT-133. The flowfield analysis has centred upon the vortex-induced gust velocities measured in the immediate vicinity outside and inside of trailing-pair vortex cores, mildly perturbed in non-turbulent atmospheres, at very large Reynolds Numbers of 2-3x1012, based upon induced wind-speed and axial length of the trailing vortices. Vortex-induced core and outside-core profiles were determined by vector-differencing of air and inertial velocity vectors. Kinematic geometry was used to estimate vortex centre and radial distance from the centre. Core radius was defined by peak vortex-induced velocity. Generally, discrete gust vortex-induced velocity profiles were found to consist of primary, secondary and tertiary vortex elements. Combinations of primary and secondary elements were prevalent, with peaks of 25 ms-1 and core radii of 2-6 m, and resulted in sharp-peaked velocity profiles, adequately described by the potential or Rankine vortex model. Occasionally, the profiles were rounded with no secondary or tertiary elements - such profiles were adequately described by the Burnham-Hallock model. Tertiary vortex elements were small and intense, induced wind speeds and core radii to approximately 35-45 ms-1 and 0.3-0.6 m, respectively When normalized, and considered statistically - about 25% of profiles were of Burnham-Hallock shape with low turbulence levels. The remainder were full-shape profiles: 50% of profiles were between B-H and potential profiles, whilst 25% of profiles had induced velocities greater than potential, of which 5% were > twice potential peak velocity. Numerical differentiation of the profiles showed that many of profiles were characterized by a strong Rankine radial mode instability between.95rC and 1.5rC. The instability was harmonically mirrored at 2rC and 4rC. Radial analysis indicated that strong, unsteady radial velocities existed for the full-profiles (but not B-H profiles) near core edges and inside cores. The radial flows were both in-flows and outflows. Associated with the inflows was intensification of quasi-vorticity, wherefore spatial gradients of wind gusts were measured under the assumption of frozen-flow, at small scale level. © 2011 by National Research Council Canada. |
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