Vortex structure and dynamics in the near field of a coaxial jet

Dahm, Werner J. A.; Frieler, C. E.; Tryggvason, Grétar

doi:10.1017/s0022112092002088

Cited by 151 publications

(137 citation statements)

References 11 publications

(15 reference statements)

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“…φ 2 = 0, these equations were derived earlier in [8], but without the simplification derived next. Using the circulation formula ( 3.17) for helical flow the equation for ψ t can be considerably simplified.…”

Section: Vortex Sheets With Helical Symmetrymentioning

confidence: 99%

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Lagrangian theory for 3D vortex sheets with axial or helical symmetry

Caflisch¹,

Li²

1992

Transport Theory and Statistical Physics

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Consider a three-dimensional vortex sheet in inviscid, incompressible flow which is irrotational away from the sheet. We derive an equation for the evolution of a vortex sheet in Lagrangian coordinates, i.e. an equation that is restricted to the sheet itself and is analogous to the Birkhoff-Rott equation for a two-dimensional (planar) sheet. This general equation is specialized to sheets with axial or helical symmetry, with or without swirl.

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Section: Vortex Sheets With Helical Symmetrymentioning

confidence: 99%

“…The equations for an axisymmetric vortex sheet without swirl have been derived and numerically solved in [2,3,4,5,7,8,12,13].…”

Section: Introductionmentioning

confidence: 99%

Lagrangian theory for 3D vortex sheets with axial or helical symmetry

Caflisch¹,

Li²

1992

Transport Theory and Statistical Physics

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“…One in the region between the jet and the environment, called the outer shear layer, and one in the region between the CRZ and the jet, called the inner shear layer. 8,9 These shear layers are characterized by strong anisotropic turbulence. Although the annular jet geometry is axisymmetric, under some conditions the flow exhibits a spontaneous break in symmetry.…”

Section: Introductionmentioning

confidence: 99%

Symmetry breaking and vortex precession in low-swirling annular jets

et al. 2014

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In this paper, the flow dynamics in the wake of a turbulent annular jet is studied using Time-Resolved Stereoscopic Particle Image Velocimetry and Proper Orthogonal Decomposition (POD). In this wake, a central recirculation zone is present which, under certain conditions, shows a low-frequency precessing motion. POD analysis of the measured velocity data shows that at zero swirl, an asymmetry is present in the wake, which motion is random in time. This asymmetry originates from a bifurcation of the flow once a threshold Reynolds number is exceeded. For low-swirl numbers, ranging from 0 < S < 0.12, the asymmetry is still present and its motion becomes structured into a well defined precession. For S > 0.12, the precession is gone and the motion of the asymmetric wake is again random in time, similar like the non-swirling jet. In this paper, a model is developed to describe the influence of swirl on the wake dynamics. The model assumes that perturbations in the inner shear layer near the bluff body wall are convected towards the stagnation point. These perturbations cause a shift in the stagnation points position. This shift is convected back to the inner shear layer through convection in the recirculating flow. The dynamics of this feedback mechanism can be modeled by the nonlinear delayed saturation model. In this paper, the model is adapted for swirling flow and simulations show that good agreement is found with the experiments.

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“…Many flow visualization experiments have been undertaken to understand the behavior of the turbulent eddies in the inner shear layer. Dahm et al performed flow visualization experiments in the near field region of a coaxial jet for different velocity ratios and velocity magnitudes using laser-induced-fluorescence (LIF) technique with still photographs (17). Two of the velocity ratios they investigated, 1 and 2.56, are of particular interest because they are similar to the operating conditions in the research discussed here.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Coal Particle Flow Patterns in Low Nox Burners

Yurteri¹,

Ogden

Sinclair

et al. 2001

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It is well understood that the stability of axial diffusion flames is dependent on the mixing behavior of the fuel and combustion air streams. Combustion aerodynamic texts typically describe flame stability and transitions from laminar diffusion flames to fully developed turbulent flames as a function of increasing jet velocity. Turbulent diffusion flame stability is greatly influenced by recirculation eddies that transport hot combustion gases back to the burner nozzle. This recirculation enhances mixing and heats the incoming gas streams. Models describing these recirculation eddies utilize conservation of momentum and mass assumptions. Increasing the mass flow rate of either fuel or combustion air increases both the jet velocity and momentum for a fixed burner configuration. Thus, differentiating between gas velocity and momentum is important when evaluating flame stability under various operating conditions. The research efforts described herein are part of an ongoing project directed at evaluating the effect of flame aerodynamics on NO x emissions from coal fired burners in a systematic manner. This research includes both experimental and modeling efforts being performed at the University of Arizona in collaboration with Purdue University. The objective of this effort is to develop rational design tools for optimizing low NO x burners. Experimental studies include both coldand hot-flow evaluations of the following parameters: primary and secondary inlet air velocity, coal concentration in the primary air, coal particle size distribution and flame holder geometry. Hot-flow experiments will also evaluate the effect of wall temperature on burner performance.Cold-flow experiments were conducted at Purdue University using a 0.45 meter square Plexiglas down-flow flow visualization chamber. The 1 meter tall chamber was equipped with X-Y-Z traversing laser doppler velocimetry/phase doppler particle analyzer (LDV/PDPA). The overall purpose of the cold-flow research is to investigate the gas-solid interactions and particle motion in an isothermal coaxial jet as a function of various inlet parameters including velocity ratio and of particle properties: particle size and the particle size distribution. By utilizing a bimodal mixture of large and small particles, we can more closely approximate the flow characteristics of pulverized coal streams, and enables us to study the possible changes in the particle behavior of different sizes in the presence one another. Lagrangian particle tracking was employed to help verify the proposed mechanism for particle motion and gas-solid interaction for different velocity ratios.A computational study using the Fluent 4.5 CFD package was performed to evaluate the predictive capability of the standard k-ε turbulent model for the coaxial jet flow behavior and to calculate particle trajectories and compare these to the cold-flow results. The standard k-ε model relates the Reynolds stress using the Boussinesq eddy viscosity assumption. While, the Boussinesq eddy-viscosity model de...

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Vortex structure and dynamics in the near field of a coaxial jet

Cited by 151 publications

References 11 publications

Lagrangian theory for 3D vortex sheets with axial or helical symmetry

Lagrangian theory for 3D vortex sheets with axial or helical symmetry

Symmetry breaking and vortex precession in low-swirling annular jets

Optimization of Coal Particle Flow Patterns in Low Nox Burners

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