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Holographic particle image velocimetry measurements of hairpin vortices in a subcritical air channel flow
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View: Figures


Image of FIG. 1.
FIG. 1.

The air channel facility. All dimensions are given in millimeters.

Image of FIG. 2.
FIG. 2.

Undisturbed streamwise velocity profiles measured at and . 엯, ; ●, ; ▴, ; ∎, ; ◆, ; - - - corresponds to the parabolic profile.

Image of FIG. 3.
FIG. 3.

A schematic drawing of the condensation particle generator.

Image of FIG. 4.
FIG. 4.

Time-sequence midplane visualization of hairpins. Field of view is , ; , .

Image of FIG. 5.
FIG. 5.

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.

Image of FIG. 6.
FIG. 6.

The effect of a small disturbance amplitude on the evolution of the CVP . (a) ; (b) ; (c) .

Image of FIG. 7.
FIG. 7.

Hairpin vortices generated by large-amplitude disturbances at Reynolds number of . (a) ; (b) ; (c) .

Image of FIG. 8.
FIG. 8.

Trajectories of hairpins’ heads .

Image of FIG. 9.
FIG. 9.

Convection velocity of the hairpins’ heads (, ). ▴, 2D visualization measurements; ⊗, HPIV measurements. The solid line represents a linear fit to the 2D measurements.

Image of FIG. 10.
FIG. 10.

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.

Image of FIG. 11.
FIG. 11.

The 3D instantaneous structure of a single hairpin (, ), looking upstream (a), downstream (b), and from the side (c).

Image of FIG. 12.
FIG. 12.
Image of FIG. 13.
FIG. 13.

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).

Image of FIG. 14.
FIG. 14.

(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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Scitation: Holographic particle image velocimetry measurements of hairpin vortices in a subcritical air channel flow