The air channel facility. All dimensions are given in millimeters.
Undisturbed streamwise velocity profiles measured at and . 엯, ; ●, ; ▴, ; ∎, ; ◆, ; - - - corresponds to the parabolic profile.
A schematic drawing of the condensation particle generator.
Time-sequence midplane visualization of hairpins. Field of view is , ; , .
A schematic illustration of the generation of a counter-rotating vortex pair (CVP) due to the interaction between the base plane Poiseuille flow (black arrows) and the cross-flow jet emerging from a rectangular streamwise slot (white arrows). (a) Cross-section view; (b) perspective view.
The effect of a small disturbance amplitude on the evolution of the CVP . (a) ; (b) ; (c) .
Hairpin vortices generated by large-amplitude disturbances at Reynolds number of . (a) ; (b) ; (c) .
Trajectories of hairpins’ heads .
Convection velocity of the hairpins’ heads (, ). ▴, 2D visualization measurements; ⊗, HPIV measurements. The solid line represents a linear fit to the 2D measurements.
Shedding frequency versus injection velocity. Black symbols correspond to the present measurements, the error bars show their associated standard deviations, empty and gray symbols correspond to the results of Ref. 8, and the solid line represents an empirical fit. The encircled and empty symbols denote data points which do not follow the fit.
The 3D instantaneous structure of a single hairpin (, ), looking upstream (a), downstream (b), and from the side (c).
Disturbance threshold versus Reynolds number for three kinds of base flow: ●, plane Poiseuille air flow; 엯, water boundary layer (Ref. 8); ◻, rotating shear flow (Ref. 11).
(Color). Comparison of the distributions of the vertical vorticity along the hairpin structure between (a) DNS results for a Gaussian vortex in uniform shear obtained at (Ref. 23) and (b) present HPIV measurements at . (c) A close-up of the high-intensity spot of the vertical vorticity shown in Fig. 12(b).
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