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Three-dimensional numerical simulation of hydrodynamic interactions between pectoral-fin vortices and body undulation in a swimming fish
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10.1063/1.3640080
/content/aip/journal/pof2/23/9/10.1063/1.3640080
http://aip.metastore.ingenta.com/content/aip/journal/pof2/23/9/10.1063/1.3640080
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(Color online) Schematic illustration of the mechanism of vortex control for saving locomotive energy in a diamond-shaped fish school. The circles with arrows denote the reversed Kármán vortex street shed by the fish swimming upstream. The blue arrows represent fluid jets formed inside the reversed Kármán vortex street. The block arrows represent upward oriented flow formed by the reversed Kármán vortex street. Dashed lines are drawn to highlight the diamond shape of the fish school.

Image of FIG. 2.
FIG. 2.

(Color online) A fish swimming with pectoral fins abducted.

Image of FIG. 3.
FIG. 3.

(Color online) Schematic diagram illustrating arrangement of the physical model and computational domain.

Image of FIG. 4.
FIG. 4.

(a) Amplitude envelope of the body wave. (b) The undulatory body of the fish model.

Image of FIG. 5.
FIG. 5.

The independence of the grid and of the time step during one undulation cycle for flow over a swimming fish with the pectoral fins abducted at St = 0.8. The net longitudinal force coefficient (CD ) and net lateral force coefficient (CL ) were evaluated (a) for the entire fish model consisting of both the body and pectoral fins and (b) for solely the pectoral fins. Dashed lines: mesh number 3.2 × 105, dimensionless time step 0.02; solid lines: mesh number 6.4 × 105, dimensionless time step 0.01. The dashed lines agree satisfactorily with their corresponding solid lines.

Image of FIG. 6.
FIG. 6.

Variation of the net lateral force coefficient (CL ) within an undulation cycle for various Strouhal numbers.

Image of FIG. 7.
FIG. 7.

(Color online) The undulating movement of a fish swimming at various Strouhal numbers with the pectoral fins abducted, corresponding to time instant t/T = 0.2. The blue solid arrow denotes the moving direction of the undulating fish body. The outline of the fish body is highlighted in blue.

Image of FIG. 8.
FIG. 8.

(Color online) Vorticity contours (ωz ) of flow fields observed on the horizontal midplane (z = 0) intersecting a fish swimming at St = 0. The black dashed ellipses with arrows denote the pectoral-fin vortices and their direction of rotation. (a)–(f) Six sequential images illustrating the periodic and symmetric shedding of pectoral-fin vortices.

Image of FIG. 9.
FIG. 9.

(Color online) Vorticity contours (ωz ) of fish flow fields observed on the horizontal midplane (z = 0) for St = 0.1. The blue solid arrow denotes the moving direction of the undulating fish body. The black dashed ellipses with arrows denote the pectoral-fin vortices and their direction of rotation. (a)–(f) Six sequential images illustrating the periodic and asymmetric shedding of pectoral-fin vortices.

Image of FIG. 10.
FIG. 10.

(Color online) Pressure contours of the fish flow fields shown in Fig. 9, for a fish swimming at St = 0.1. The blue solid arrow denotes the direction of fish body movement.

Image of FIG. 11.
FIG. 11.

(Color online) Vorticity contours (ωz ) of flow fields observed on the horizontal midplane (z = 0) intersecting a fish swimming at St = 0.8. The blue solid arrow denotes the moving direction of the undulating fish body. The black dashed ellipses with arrows denote the pectoral-fin vortices and their direction of rotation.

Image of FIG. 12.
FIG. 12.

(Color online) Pressure contours of the fish flow fields shown in Fig. 11. The blue solid arrow denotes the direction of fish body movement.

Image of FIG. 13.
FIG. 13.

(Color online) Vorticity contours (ωz ) of flow fields observed on the horizontal midplane (z = 0) intersecting a fish swimming with the pectoral fins (a) adducted and (b) abducted. The brighter and darker colors of the contour represent positive and negative vorticity values, respectively. The blue and black solid arrows denote, respectively, the directions of body-wave velocity (V) and background free-stream velocity (U). The black dashed ellipses with arrows denote the pectoral-fin vortices and their direction of rotation, with Uvortex representing the velocity of the recirculating flow near the fish-body surface. (c) Cycle-averaged friction-force coefficient () versus Strouhal number.

Image of FIG. 14.
FIG. 14.

(Color online) Pressure contours of flow fields observed on the horizontal midplane (z = 0) intersecting a fish swimming with pectoral fins (a) adducted and (b) abducted. The brighter and darker colors of the contour, respectively, represent negative and positive pressure values. (c) Cycle-averaged pressure-force coefficient () versus Strouhal number.

Image of FIG. 15.
FIG. 15.

(Color online) Energy-saving mechanism in a fish swimming with the pectoral fins abducted. (a) Pressure contour of the fish flow field observed on the horizontal midplane (z = 0). The brighter and darker colors of the contour, respectively, represent negative and positive pressure values. The blue dashed arrow denotes the direction of local movement of the undulating fish body. The black dashed ellipses with arrows denote the pectoral-fin vortices and their direction of rotation. The two vertical, dashed, and black lines specify the borders of the section alongside the upper surface at which the power-consumption coefficient (CP ) exhibited in (b) is evaluated.

Image of FIG. 16.
FIG. 16.

(Color online) Schematic illustrations for the proposed biohydrodynamic analogy. (a) A fish swimming with the pectoral fins abducted. (b) A fish swimming behind an upstream D-shaped obstacle. (a) and (b) The black dashed ellipses with arrows denote the shed vortices and their direction of rotation. The blue solid arrows denote the direction of motion of the fish body. The black dashed rectangles highlight the vortex “generator”; the blue dashed rectangles highlight the vortex ‘adapter’. Both abducted pectoral fins and the D-shaped obstacle act like a vortex generator that sheds vortices downstream. Both the fish body posterior to the abducted pectoral fins and the fish slaloming behind the D-shaped obstacle act like a vortex adapter.

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/content/aip/journal/pof2/23/9/10.1063/1.3640080
2011-09-26
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Three-dimensional numerical simulation of hydrodynamic interactions between pectoral-fin vortices and body undulation in a swimming fish
http://aip.metastore.ingenta.com/content/aip/journal/pof2/23/9/10.1063/1.3640080
10.1063/1.3640080
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