Two-frame 3D particle tracking

Pereira, Francisco; Stüer, Heinrich; Graff, Emilio C.; Gharib, Morteza

doi:10.1088/0957-0233/17/7/006

Cited by 151 publications

(124 citation statements)

References 25 publications

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“…In order to analyse the three-dimensional dynamics of vortex rings such as the oval vortex ring and AR4 elliptical vortex ring considered in this study, three-dimensional velocimetry is required. The three-dimensional, threecomponent defocusing digital particle image velocimetry (DDPIV) technique (Willert & Gharib 1992;Pereira & Gharib 2002;Pereira et al 2006) has been applied successfully to non-axisymmetric vortex ring flows by Troolin & Longmire (2009) and Kim & Gharib (2011), and is a promising candidate for performing three-dimensional velocimetry measurements on vortex rigs undergoing large deformations.…”

Section: O'farrell and J O Dabirimentioning

confidence: 99%

Pinch-off of non-axisymmetric vortex rings

O’Farrell

Dabiri

2014

J. Fluid Mech.

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The formation and pinch-off of non-axisymmetric vortex rings is considered experimentally. Vortex rings are generated using a non-circular piston-cylinder arrangement, and the resulting velocity fields are measured using digital particle image velocimetry. Three different nozzle geometries are considered: an elliptical nozzle with an aspect ratio of two, an elliptical nozzle with an aspect ratio of four and an oval nozzle constructed from tangent circular arcs. The formation of vortices from the three nozzles is analysed by means of the vorticity and circulation, as well as by investigation of the Lagrangian coherent structures in the flow. The results indicate that, in all three nozzles, the maximum circulation the vortex can attain is determined by the equivalent diameter of the nozzle: the diameter of a circular nozzle of identical cross-sectional area. In addition, the time at which the vortex rings pinch off is found to be constant along the nozzle contours, and independent of relative variations in the local curvature. A formation number for this class of vortex rings is defined based on the equivalent diameter of the nozzle, and the formation number for vortex rings of the three geometries considered is found to lie in the range of 3-4. The implications of the relative shape and local curvature independence of the formation number on the study and modelling of naturally occurring vortex rings such as those that appear in biological flows is discussed.

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Section: O'farrell and J O Dabirimentioning

confidence: 99%

Pinch-off of non-axisymmetric vortex rings

O’Farrell

Dabiri

2014

J. Fluid Mech.

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“…A curved rigid plate, which has a similar shape to the flexible plate at its maximum deformation, was also chosen for comparison with the other cases. In order to map three-dimensional flow fields present in this study, we implemented defocusing digital particle image velocimetry (DDPIV, Willert & Gharib 1992;Pereira & Gharib 2002;Pereira et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Flexibility effects on vortex formation of translating plates

Kim

Gharib

2011

J. Fluid Mech.

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Vortex structures made by impulsively translating low aspect-ratio plates are studied experimentally using defocusing digital particle image velocimetry. The investigation of translating plates with a 90• angle of attack is important since it is a fundamental model for a better understanding of drag-based propulsion systems. Rectangular flatrigid, flexible and curved-rigid thin plates with the same aspect ratio are studied in order to develop qualitative and quantitative understanding of their vortex structures and hydrodynamic forces. We find that the vortex formation processes of all three cases are drastically different from each other. The interaction of leading-edge vortices and tip flow near the tip region is an important mechanism to distinguish vortex patterns among these three cases. The drag trends of three cases are correlated closely with vortex structure and circulation. The initial peak of hydrodynamic force in the flexible plate case is not as large as the initial peak of the flat and curved rigid plate cases during the acceleration phase. However, after the initial peak, the flexible plate generates a large force comparable to that of the flat-rigid plate case in spite of its deformed shape, which results from the slow development of the vortex structure.

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“…We also examined single-plate cases by removing one plate in order to compare the single-plate and double-plate cases. Defocusing digital particle image velocimetry (DDPIV) (Willert & Gharib 1992;Pereira & Gharib 2002;Pereira et al 2006) was used to study the three-dimensional flow fields, and a load cell was used for force measurements. This paper is organized as follows.…”

Section: Introductionmentioning

confidence: 99%

“…Image pairs were recorded in a double-exposure mode with a time gap of 5 ms between laser pulses. The images from the DDPIV camera were processed with in-house 8 D. Kim, F. Hussain and M. Gharib DDPIV software based on Pereira & Gharib (2002) and Pereira et al (2006). The three-dimensional coordinates of the particles inside the tank were found by matching particle images of the three CCDs.…”

Section: Introductionmentioning

confidence: 99%

“…The three-dimensional coordinates of the particles inside the tank were found by matching particle images of the three CCDs. Velocity vectors calculated by a three-dimensional particle tracking scheme (Pereira et al 2006) were randomly spaced in a measurement volume of 160 mm × 160 mm × 160 mm. The full flow field was divided into cubic grids of 3 mm × 3 mm × 3 mm.…”

Section: Introductionmentioning

confidence: 99%

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Vortex dynamics of clapping plates

2013

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Vortex formation and force generation of clapping plates with various aspect ratios (AR) and stroke angles were investigated. Experiments were performed with a pair of hinged rectangular plates that were rotated symmetrically in a static fluid, and defocusing digital particle image velocimetry was employed to measure the threedimensional flow field. Single-plate cases were also studied to compare with clapping plate cases. As AR decreases, both circulation of the tip vortex and area enclosed by the vortex loop increase inversely. An empirical power-law relationship with a negative exponent is found between total impulse and AR for a given stroke angle. The sensitivity of the force generated by the plates to the change of AR is larger at the smaller stroke angle because of faster acceleration and deceleration. The increase in impulse per plate from the single-plate case to the clapping double-plate case is larger for lower AR. These results reveal that low AR wings are more efficient in propulsive force generation in some specific modes of unsteady flapping flight. The evolution of the wake structures is found to depend on AR and stroke angle.

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Two-frame 3D particle tracking

Cited by 151 publications

References 25 publications

Pinch-off of non-axisymmetric vortex rings

Pinch-off of non-axisymmetric vortex rings

Flexibility effects on vortex formation of translating plates

Vortex dynamics of clapping plates

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