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Time-resolved particle image velocimetry measurements of vortex and shear layer dynamics in the near wake of a tethered sphere
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10.1063/1.4812181
/content/aip/journal/pof2/25/7/10.1063/1.4812181
http://aip.metastore.ingenta.com/content/aip/journal/pof2/25/7/10.1063/1.4812181

Figures

Image of FIG. 1.
FIG. 1.

Schematic layout of experimental setup and employed coordinate system. (a) Cross section, (b) top view.

Image of FIG. 2.
FIG. 2.

Example of collapsed sequence of 21 PIV images centered at / = 0.25 (Table I , = 4.84, see Fig. 7 ).

Image of FIG. 3.
FIG. 3.

Normalized, mean transverse sphere oscillation amplitude as a function of reduced velocity. Present results, = 0.182: • PIV, ○ sphere tracking; Literature results: □ = 2.8, = 0.026, = 28, = 0.228, × = 7.87, = 0.167.

Image of FIG. 4.
FIG. 4.

Time series of sphere transverse centroid positions (left column), phase diagrams and Poincaré points (middle column), and power spectra of sphere motion (right column). (a) = 3.18, (b) = 4.84, (c) = 5.97, (d) = 14.1.

Image of FIG. 5.
FIG. 5.

Instantaneous sequence of (a) vector maps, (b) vorticity, (c) swirling strength, (d) and (e) Galilean decomposed parts of vector map (full vector resolution) showing V and V, respectively; subtracted in (d) = (−0.025, 0.005) and (e) = (−0.025, 0.007) in [m/s]. = 3.18. Lightest gray (red online) vectors are reference vectors, in (a) reference vector = 0.2 [m/s]. Dashed vertical lines in (c) indicate sampling lines (see Fig. 6 ).

Image of FIG. 6.
FIG. 6.

Spatiotemporal swirling strength characteristics for = 3.18 sampled at (a) / = 0.5, (b) / = 0.7. Sampling lines are indicated as vertical dashed lines in Fig. 5 (enhanced online). [URL: http://dx.doi.org/10.1063/1.4812181.1]doi: 10.1063/1.4812181.1.

Image of FIG. 7.
FIG. 7.

Instantaneous sequence of (a) vector maps, (b) vorticity, (c) swirling strength. = 4.84. Vector maps were Galilean decomposed by subtracting = (0.02, −0.08), (−0.008, 0.01), (0.0015, 0.01), (0,0) in [m/s] for / = 0, 0.25, 0.5, and 0.75, respectively. Lightest gray (red online) vector in (a) denotes reference vector: 0.2 [m/s].

Image of FIG. 8.
FIG. 8.

Instantaneous sequence of (a) vector maps, (b) vorticity, (c) swirling strength. = 5.97. Vector maps were Galilean decomposed by subtracting = (0.0859, 0), (0.003, 0), (0, 0), (−0,0962, 0) in [m/s] for / = 0, 0.25, 0.5, and 0.75, respectively. Lightest gray (red online) vector in (a) denotes reference vector: 0.2 [m/s]. Vertical dashed line denotes sampling position (see Fig. 10 ).

Image of FIG. 9.
FIG. 9.

Transverse locations of shear layer and sphere center as a function of time. (a) = 4.84, (b) = 5.97. Solid and dashed vertical lines indicate zero angle shear layer inclination. ▵ / = 0.88, □ / = 0.52, ◯ / = 0.16, — sphere transverse motion.

Image of FIG. 10.
FIG. 10.

Spatiotemporal characteristics sampled at / = 0.6, = 4.84. (a) Vorticity, (b) swirling strength (enhanced online). [URL: http://dx.doi.org/10.1063/1.4812181.2]doi: 10.1063/1.4812181.2.

Image of FIG. 11.
FIG. 11.

Spatiotemporal characteristics sampled at / = 0.7, = 5.97. (a) Vorticity, (b) swirling strength (enhanced online). [URL: http://dx.doi.org/10.1063/1.4812181.3]doi: 10.1063/1.4812181.3.

Image of FIG. 12.
FIG. 12.

Instantaneous sequence of vorticity (left column) and swirling strength (right column) maps for = 4.84 showing the pinch-off of V. (a) / = 0.374, (b) / = 0.435, (c) / = 0.523, (d) / = 0.611. Time between frames, Δ = 40/700 s.

Image of FIG. 13.
FIG. 13.

Instantaneous sequence of vorticity and swirling strength maps showing vortex-shear layer interaction and shear layer pinch-off for = 5.97 at / = (a) 0.692, (b) 0.736, (c) 0.780, (d) 0.824, (e) 0.868, (f) 0.912, (g) 0.956, (h) 1.0. Time between frames: Δ = 20/700 s.

Image of FIG. 14.
FIG. 14.

Instantaneous sequence of (a) vector maps, (b) vorticity, (c) swirling strength. = 14.1. Vector maps were Galilean decomposed by subtracting = (0.16, 0), (0.07, −0.04), (−0.05, 0.06), (0, 0) in [m/s] for / = 0, 0.25, 0.5, and 0.75, respectively. Lightest gray (red online) vector in (a) denotes reference vector: 0.2 [m/s]. Vertical dashed lines denote sampling positions (see Fig. 15 ).

Image of FIG. 15.
FIG. 15.

Spatiotemporal swirling strength characteristics for = 14.1 sampled at (a) / = 0.7, (b) / = 1.0. The sampling lines are depicted as dashed lines in Fig. 14 (enhanced online). [URL: http://dx.doi.org/10.1063/1.4812181.4]doi: 10.1063/1.4812181.4.

Image of FIG. 16.
FIG. 16.

Power spectrum of transverse velocity fluctuations in the shear layer at = 14.1. Dashed rectangle and horizontal bar indicate measured broad peak and predicted range of (Eq. (1)). + Frequencies estimated from Fig. 15 .

Tables

Generic image for table
Table I.

Experimental parameters of TR-PIV measurements. Conditions I–III contain three data sets, condition IV, two data sets.

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/content/aip/journal/pof2/25/7/10.1063/1.4812181
2013-07-17
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Time-resolved particle image velocimetry measurements of vortex and shear layer dynamics in the near wake of a tethered sphere
http://aip.metastore.ingenta.com/content/aip/journal/pof2/25/7/10.1063/1.4812181
10.1063/1.4812181
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