Effects of trailing jet instability on vortex ring formation

Zhao, Wei; Frankel, Steven; Mongeau, Luc

doi:10.1063/1.870264

Cited by 69 publications

(71 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Reynolds numbers considered here are comparable with those observed in jetting swimmers such as paralarval and juvenile squid (O'Dor 1988; Bartol et al 2009) and several species of jellyfish (Gladfelter 1973;Colin & Costello 2002;Peng & Dabiri 2009), which have been observed to operate at Reynolds numbers in the range of 10 2 -10 3 . We did not consider the effects of varying the Reynolds number, since they have been previously characterized for circular vortex rings, and found to have little impact on the formation number, in the intermediate range of Reynolds numbers (Rosenfeld et al 1998;Mohseni et al 2000;Zhao et al 2000).…”

Section: Experimental Methodsmentioning

confidence: 99%

“…In particular, Rosenfeld et al (1998), Zhao, Frankel & Mongeau (2000) and Mohseni et al (2000), found the Reynolds number to have little impact on the formation number, provided that Re Γ is sufficiently large to ensure the formation process is completed before viscosity has a significant impact (Re Γ > 2000 according to Mohseni et al (2000)). The concept of the universal formation number has also been extended to more complex vortex generator setups and computational frameworks, by extending the definition of the dimensionless vortex formation time to allow for variations such as the presence of bulk coflow (Krueger et al 2006) or bulk counterflow (Dabiri & Gharib 2004a), a time-varying exit diameter (Mohseni et al 2000;Dabiri & Gharib 2005), and differing velocity programs (Rosenfeld et al 1998;Mohseni et al 2000;Krueger & Gharib 2003;Olcay & Krueger 2010) and velocity profiles (Rosenfeld et al 1998).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Pinch-off of non-axisymmetric vortex rings

O’Farrell

Dabiri

2014

J. Fluid Mech.

View full text Add to dashboard Cite

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.

show abstract

Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Pinch-off of non-axisymmetric vortex rings

O’Farrell

Dabiri

2014

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…and U b (r, τ ) describes the radial dependence of the profile For the piston velocity program we used the model suggested by Zhao et al (2000):…”

Section: Physical and Numerical Parametersmentioning

confidence: 99%

A model for confined vortex rings with elliptical-core vorticity distribution

2016

View full text Add to dashboard Cite

We present a new model for an axisymmetric vortex ring confined in a tube. The model takes into account the elliptical (elongated) shape of the vortex ring core and thus extends our previous model [Danaila, Kaplanski and Sazhin, J. of Fluid Mechanics, 774, 2015] derived for vortex rings with quasi-circular cores. The new model offers a more accurate description of the deformation of the vortex ring core, induced by the lateral wall, and a better approximation of the translational velocity of the vortex ring, compared with the previous model. The main ingredients of the model are the following: the description of the vorticity distribution in the vortex ring is based on the previous model of unconfined elliptical-core vortex rings [Kaplanski, Fukumoto and Rudi, Physics of Fluids, 24, 2012]; Brasseur's approach [Brasseur, PhD Thesis, 1979] is then applied to derive a wall-induced correction for the Stokes stream function of the confined vortex ring flow. We derive closed formulae for the flow stream function and vorticity distribution. An asymptotic expression for the long time evolution of the drift velocity of the vortex ring as a function of the ellipticity parameter is also derived. The predictions of the model are shown to be in agreement with direct numerical simulations of confined vortex rings generated by a piston-cylinder mechanism. The predictions of the model support the recently suggested heuristic relation [Krieg and Mohseni, J. Fluid Engineering, 135, 2013] between the energy and circulation of vortex rings with converging radial velocity. A new procedure for fitting experimental and numerical data with the predictions of the model is described. This opens the way for applying the model to realistic confined vortex rings in various applications including those in internal combustion engines.

show abstract

“…Instabilities in the trailing jet can also affect the formation of the leading ring. Zhao et al (2000) found that trailing instabilities can accelerate detachment of the leading vortex thus reducing its final circulation and formation number.…”

Section: Introductionmentioning

confidence: 99%

“…Numerical studies by Rosenfeld et al (1998) (hereafter, RRG) and Zhao et al (2000) have examined the parameters affecting the formation number for transient jets, finding a strong dependence on the velocity profile and a weak, but significant, dependence on the velocity program. Smoothing the velocity profile can decrease the formation number, while smooth accelerations can increase the value.…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization of starting jet dynamics

et al. 2007

View full text Add to dashboard Cite

The dynamics of a laminar starting jet are explored in a series of laboratory experiments and numerical simulations. We identify new, objective methods for characterizing the leading vortex ring, enabling robust comparisons with results from a numerical model. Observations of circulation in the initial vortex ring and for the total jet are reported along with strain rate at the leading stagnation point. Growth and pairing of shear instabilities trailing the leading vortex ring is observed. Development of these secondary vortices and their subsequent interactions with the leading vortex has significant effects on the characteristics of the primary vortex ring. Strong fluctuations in strain rate at the leading edge are associated with the pairing of the initial vortex ring with a trailing secondary ring.

show abstract

Effects of trailing jet instability on vortex ring formation

Cited by 69 publications

References 12 publications

Pinch-off of non-axisymmetric vortex rings

Pinch-off of non-axisymmetric vortex rings

A model for confined vortex rings with elliptical-core vorticity distribution

Experimental characterization of starting jet dynamics

Contact Info

Product

Resources

About