A large-eddy simulation study on vortex-ring collisions upon round cylinders

New, T. H.; Gotama, Gabriel Jeremy; Vevek, U S

doi:10.1063/5.0057475

Cited by 12 publications

(15 citation statements)

References 42 publications

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“…On the other hand, the collision behaviour along the cylinder straight edges is more reminiscent of vortex ring collisions with flat walls, with vortex stretching effects leading to increasingly smaller vortex structures accompanying reductions in the cylinder diameter ratio. In the follow-up large-eddy simulations (LES) study by New et al (2021), simulation results showed good agreement with the vortex flow models proposed in the earlier study, and revealed further that the vortex ringlets undergo axis-switching like elliptic vortex rings. In addition, vortex core trajectories along the convex surface plane extracted from the numerical results also agree well with the experimental results, on top of allowing more accurate trajectory extraction of the vortex cores along the cylinder straight edges.…”

Section: Introductionsupporting

confidence: 79%

“…2007; Cheng, Lou & Luo 2010; Couch & Krueger 2011; New, Shi & Zang 2016; Xu & Wang 2016; Mishra, Pumir & Ostilla-Mónico 2021), porous walls (Adhikari & Lim 2009; Hrynuk, Van Luipen & Bohl 2012; Naaktgeboren, Krueger & Lage 2012; Cheng, Lou & Lim 2014; Xu et al. 2018), and concave or convex surfaces (New & Zang 2017; New, Gotama & Vevek 2021; Chen, Gao & Chen 2022; Ahmed & Erath 2023), and under confined conditions (Stewart et al. 2012; Danaila, Kaplanski & Sazhin 2017; Zhang & Rival 2020; Hu & Peterson 2021), among others, with the primary interest surrounding how the vortex dynamics unfolds during the collisions and how it differs when the scenario varies.…”

Section: Introductionmentioning

confidence: 99%

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Collisions of vortex rings with hemispheres

New,

Xu,

Shi

2024

J. Fluid Mech.

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A numerical investigation was conducted on $Re_{\varGamma _{0}}=3000$ vortex rings colliding with wall-mounted hemispheres to study how their relative sizes affect the resulting vortex dynamics and structures. The hemisphere to vortex ring diameter ratio ranges from $D/d=0.5$ to $D/d=2$ . Secondary/tertiary vortex rings are observed to result from hemispheric surface boundary layer separations rather than wall boundary layer separations as the diameter ratio increases. While those for $D/d\leq 1$ hemispheres can be attributed to sequential hemispheric and wall boundary layer separations, the primary vortex ring produces a series of secondary/tertiary vortex rings only along the $D/d=2$ hemispheric surface. This indicates that the presence of the wall makes little difference when the hemisphere is sufficiently large. On top of comparing vortex ring circulations and translational velocities between hemisphere and flat-wall based collisions, present collision outcomes have also been compared with those predicted by specific discharge velocity models. Additionally, comparisons of vortex core trajectories and vortex ring formation locations with earlier cylindrical convex surface based collisions provide more clarity on differences between two- and three-dimensional convex surfaces. Finally, vortex flow models are presented to account for the significantly different flow behaviour as the hemisphere size varies. Specifically, the vortex flow model for the $D/d=2$ hemisphere hypothesizes that the recurring tertiary vortex ring formations cease only when the primary vortex ring slows down sufficiently for the last tertiary vortex ring to entangle with it and render it incoherent. Until that happens, the primary vortex ring will continue to induce more tertiary vortex rings to form, with potential implications for heat/mass transfer optimizations.

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Section: Introductionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Collisions of vortex rings with hemispheres

New,

Xu,

Shi

2024

J. Fluid Mech.

Self Cite

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“…While the dynamic Smagorinsky model (Germano et al 1991;Lilly 1992), with the Smagorinsky constant computed in terms of the local flow conditions, is often used for jet flows, the classical Smagorinsky model has been shown to produce comparable accuracy in a number of recent investigations of vortex ring related flows at a similar Re (e.g. New, Gotama & Vevek 2021). As to the discretisation specifics, PISO (pressure-implicit with splitting of operators) is employed in the pressure velocity coupling algorithm (Issa 1986); a second-order difference scheme was implemented for all the spatial derivative terms, and the time step set at 1 × 10 −4 ensuring a maximum Courant-Friedrichs-Lewy (CFL) number below 1 for all the flow cases explored.…”

Section: Mesh Decomposition Methods Of Solution and Validationmentioning

confidence: 99%

Formation and evolution of vortex rings with weak to moderate swirl

Ortega-Chavez,

Gan,

Gaskell

2023

J. Fluid Mech.

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The formation of swirling vortex rings and their early time evolution, resulting from the controlled discharge of an incompressible, Newtonian fluid into a stationary equivalent fluid bulk, is explored for weak to moderate swirl number $S \in [0, 1]$ . Two practically realisable inlet conditions are investigated with swirl simultaneously superposed onto a linear momentum discharge; the corresponding circulation based Reynolds number is 7500. The results obtained reveal that for $S > 1/2$ , the addition of swirl promotes the breakdown of the leading primary vortex ring structure, giving rise to the striking feature of significant negative azimuthal vorticity generation in the region surrounding the primary vortex ring core, whose strength scales with ${S}^2$ . Through a nonlinear interaction with the vortex breakdown, the radius of the primary toroidal vortex core is rapidly increased; consequently, the self-induced propagation velocity of the leading ring decreases with $S$ and vortex stretching along the circular primary vortex core increases counteracting viscous diffusion effects. The latter governs the evolution of the peak vorticity intensity and the swirl velocity magnitude in the primary ring core, the circulation growth rate of the primary ring, as well as the vorticity intensity of the trailing jet and hence its stability. This combination of effects leads to an increased dimensionless kinetic energy for the primary ring with increasing $S$ and results in an almost linearly decreasing circulation based formation number, $F$ .

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“…Structured grid used in this study. The accuracy of different turbulence models was verified, including the Laminar model, 31 RSM model, and LES model 32–36 . The corresponding

{y}^{+}

values were selected for different turbulence models.…”

Section: Methodsmentioning

confidence: 99%

“…The accuracy of different turbulence models was verified, including the Laminar model, 31 RSM model, and LES model. [32][33][34][35][36] The corresponding y + values were selected for different turbulence models. For the RSM model, the high Reynolds number turbulence model requires higher y + value (30 < y + <500).…”

Section: Computational Domain and Meshmentioning

confidence: 99%

Flow characteristics and formation optimization of vortex ring air supply

et al. 2022

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The vortex rings ventilation (VRV) is a new type of air supply system comprising vortex rings. Compared with an air supply jet, a vortex ring reduces the loss of fresh air during transportation because of its stable structure. However, during the formation of the vortex ring, it entrains the ambient air and reduces the fresh air in the vortex ring. In this study, a vortex ring generator with a fresh air cavity is proposed to form confined vortex rings. This improved the fresh air ratio of the VRV. Based on previous experiments, a piston‐orifice axisymmetric model with a dynamic grid was developed to form an air vortex ring. The flow characteristics of free and confined vortex rings during the generation stage were studied. First, the evolution of free vortex rings with different stroke lengths was studied, and the optimal piston stroke length and radial constraint size were determined. Subsequently, the mixing ratios of the free and confined vortex rings were compared and analyzed. The results showed that the mixing ratio of the confined vortex ring formed by the fresh air cavity in the formation stage was zero. Moving to the location of 4.9 times the orifice diameter (D0$$ {D}_0 $$), reduced the mixing ratio of the confined vortex ring by 77.78% compared with that of the free vortex ring. In addition, the influence of three inner diameters and four outlet diameters of fresh air cavities on the vortex rings was studied to optimize the size of the vortex ring generator. The results showed that the inner diameter of the fresh air cavity was greater than 3D0$$ 3{D}_0 $$ and that an outlet diameter greater than 2.5D0$$ 2.5{D}_0 $$ had little influence on the vortex rings.

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A large-eddy simulation study on vortex-ring collisions upon round cylinders

Abstract: A large-eddy simulation study on vortex-ring collisions upon round cylinders. Physics of Fluids, 33(9), 094101-.

Cited by 12 publications

References 42 publications

Collisions of vortex rings with hemispheres

Collisions of vortex rings with hemispheres

Formation and evolution of vortex rings with weak to moderate swirl

Flow characteristics and formation optimization of vortex ring air supply

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