Paper
Spanwise vorticity structure in turbulent boundary layers

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Abstract

Four-element hot-wire probe measurements are used to examine the structure of the spanwise vorticity in the inner region of low Reynolds number zero pressure gradient turbulent boundary layers. Single-probe measurements were made over the range 1010 ≤ Rθ ≤ 4850(Rθ = θU/ν, where θ is the momentum deficit thickness, and U is the free-stream velocity), while two probe measurements were made at Rθ ≈ 1010. The present results indicate that for y+ < 50 statistical moment profiles of ωZ scale on inner variables. Event duration analyses indicate that a nearly logarithmic increase in inner normalized time scales of the ωZ bearing motions occurs with increasing Rθ. Outside the buffer region, this Rθ dependence is effectively removed if the Taylor time scale is used to normalize the event durations. Two-point correlations with probe separations in the spanwise as well as wall-normal direction are presented. In addition, the structure of the associated two-dimensional (2-D) probability distributions are examined to reveal the statistically most significant contributions underlying these correlations. Wall-normal probe separation measurements indicate the increasing prevalence of adjacent regions of opposing sign ωZ as the wall is approached. Spanwise probe separation experiments indicate the predominance of single-sign contributions, as well as increasing spatial coherence nearer the wall. The present results are interpreted to indicate that the organized spanwise vorticity-bearing motions are distributed in planes parallel to the wall for y+ less than about 12, and decrease to a nearly fixed scale outside the buffer region.

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