Simulation of particle dispersion in an axisymmetric jet

Particle dispersion in an axisymmetric jet is analysed numerically by following particle trajectories in a jet flow simulated by discrete vortex rings. Important global and local flow quantities reported in experimental measurements are successfully simulated by this method.The particle dispersion results demonstrate that the extent of particle dispersion depends strongly on γτ, the ratio of particle aerodynamic response time to the characteristic time of the jet flow. Particles with relatively small γτ values are dispersed at approximately the fluid dispersion rate. Particles with large γτ values are dispersed less than the fluid. Particles at intermediate values of γτ may be dispersed faster than the fluid and actually be flung outside the fluid mixing region of the jet. This result is in agreement with some previous experimental observations. As a consequence of this analysis, it is suggested that there exists a specific range of intermediate γτ at which optimal dispersion of particles in the turbulent mixing layer of a free jet may be achieved.

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Experiments on particle dispersion in a turbulent mixing layer

International Journal of Multiphase Flow ◽

10.1016/0301-9322(92)90081-q ◽

1992 ◽

Vol 18 (2) ◽

pp. 181-194 ◽

Cited By ~ 66

Author(s):

K. Hishida ◽

A. Ando ◽

M. Maeda

Keyword(s):

Turbulent Mixing ◽

Mixing Layer ◽

Particle Dispersion ◽

Turbulent Mixing Layer

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Numerical investigation of three-dimensionally evolving jets subject to axisymmetric and azimuthal perturbations

Journal of Fluid Mechanics ◽

10.1017/s0022112091000794 ◽

1991 ◽

Vol 230 ◽

pp. 271-318 ◽

Cited By ~ 96

Author(s):

J. E. Martin ◽

E. Meiburg

Keyword(s):

Shear Layer ◽

Vortex Ring ◽

Three Dimensional ◽

Vortex Rings ◽

Streamwise Vorticity ◽

Plane Shear ◽

Axisymmetric Jet ◽

Spatially Periodic ◽

Extensional Strain ◽

Global And Local

We study the inviscid mechanisms governing the three-dimensional evolution of an axisymmetric jet by means of vortex filament simulations. The spatially periodic calculations provide a detailed picture of the processes leading to the concentration, reorientation, and stretching of the vorticity. In the purely axisymmetric case, a wavy perturbation in the streamwise direction leads to the formation of vortex rings connected by braid regions, which become depleted of vorticity. The curvature of the jet shear layer leads to a loss of symmetry as compared to a plane shear layer, and the position of the free stagnation point forming in the braid region is shifted towards the jet axis. As a result, the upstream neighbourhood of a vortex ring is depleted of vorticity at a faster rate than the downstream side. When the jet is also subjected to a sinusoidal perturbation in the azimuthal direction, it develops regions of counter-rotating streamwise vorticity, whose sign is determined by a competition between global and local induction effects. In a way very similar to plane shear layers, the streamwise braid vorticity collapses into counter-rotating round vortex tubes under the influence of the extensional strain. In addition, the cores of the vortex rings develop a wavy dislocation. As expected, the vortex ring evolution depends on the ratio R/θ of the jet radius and the jet shear-layer thickness. When forced with a certain azimuthal wavenumber, a jet corresponding to R/θ = 22.6 develops vortex rings that slowly rotate around their unperturbed centreline, thus preventing a vortex ring instability from growing. For R/θ = 11.3, on the other hand, we observe an exponentially growing ring waviness, indicating a vortex ring instability. Comparison with stability theory yields poor agreement for the wavenumber, but better agreement for the growth rate. The growth of the momentum thickness is much more dramatic in the second case. Furthermore, it is found that the rate at which streamwise vorticity develops is strongly affected by the ratio of the streamwise and azimuthal perturbation amplitudes.

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A numerical simulation of turbulent mixing layer by discrete vortex method

10.2514/6.1984-434 ◽

1984 ◽

Cited By ~ 1

Author(s):

O. INOUE

Keyword(s):

Numerical Simulation ◽

Turbulent Mixing ◽

Mixing Layer ◽

Vortex Method ◽

Discrete Vortex ◽

Turbulent Mixing Layer ◽

Discrete Vortex Method

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Local flow topology and velocity gradient invariants in compressible turbulent mixing layer

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.235 ◽

2015 ◽

Vol 774 ◽

pp. 67-94 ◽

Cited By ~ 30

Author(s):

Navid S. Vaghefi ◽

Cyrus K. Madnia

Keyword(s):

Velocity Gradient ◽

Turbulent Mixing ◽

Probability Distributions ◽

Mixing Layer ◽

Contraction Rate ◽

Flow Topology ◽

Gradient Tensor ◽

Local Flow ◽

Turbulent Mixing Layer ◽

Turbulent Region

The local flow topology is studied using the invariants of the velocity gradient tensor in compressible turbulent mixing layer via direct numerical simulation (DNS) data. The topological and dissipating behaviours of the flow are analysed in two different regions: in proximity of the turbulent/non-turbulent interface (TNTI), and inside the turbulent region. It is found that the distribution of various flow topologies in regions close to the TNTI differs from inside the turbulent region, and in these regions the most probable topologies are non-focal. In order to better understand the behaviour of different flow topologies, the probability distributions of vorticity norm, dissipation and rate of stretching are analysed in incompressible, compressed and expanded regions. It is found that the structures undergoing compression–expansion in axial–radial directions have the highest contraction rate in locally compressed regions, and in locally expanded regions the structures undergoing expansion–compression in axial–radial directions have the highest stretching rate. The occurrence probability of different flow topologies conditioned by the dilatation level is presented and it is shown that the structures in the locally compressed regions tend to have stable topologies while in locally expanded regions the unstable topologies are prevalent.

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