Lorentz Centre, 19 Sep. 2006

Particle transport and flow modification in planar temporally evolving mixing layers

Djamel Lakehal, Chidambaram Narayanan(G. Yadigaroglu, ETH Zurich)

Adjunct Lecturer at ETH & Manager of ASCOMP GmbH(www.ascomp.ch)

Outline

Motivations: environmental concerns

Mixing layer basic flow features

Transport under 1-way coupling

Transport under 2-way coupling

Summary

Transport & dispersion of sandVolcanic ash dispersion

CO2

H20

Environmental flows with particles and droplets

Simulation: Eulerian-Lagrangian formulation

fpi

j

Fx

u

x

p

x

uu

t

u

x

u

j

j

j

j

j

j

j

2

21

0

Re

FLUID

PARTICLE

3/2

2

Re15.01

)(2

9

pd

pippp

dp

f

txuud

fdt

dvi

i

Details

Re=400, 64 X 129 Fourier Chebyshev collocation; Lx=4/Km

Tangent-hyperbolic U velocity fieldAmplitude of Fund. & Sub. modes Ef = 10-2; Es = 10-4

Rep < 1; Np = 2-4.105 particles; St= 0.3 - 5; M = 0.1-0.52nd order Runge-Kutta for Particle Equation

4th order Lagrangian ploynomial velocity interpolation

DNS of Particle dispersion in a mixing layer; St = 1.0

2D particle-laden mixing layer under 1- and 2-way Coupling: What is new ?

The analysis is Eulerian-Eulerian based

The controlling mechanisms

The mean vertical particle-phase velocity induced by KH

The correlation between particle-phase and fluid-phase modal (KH induced) stress

The effect of particle-phase modal velocity on the growth of the particle-phase mixing layer

Basic Flow Features:

1. flow evolution

2. Kinetic energy balances

Particle Transport under One-way

1. centrifuging effect

2. statistics

3. momentum balance

I- Outline: Particle Transport under 1-way Coupling

Saturation of fund. mode at t=48

initiation of pairing at t=72

end of pairing at t=96

single vortex at t=120

u=<u> +u’

u=<u> +u’

t=72 t=96

t=72 t=96

St=0.3 St=0.6 St=1

t=72

St=0.3 St=0.6 St=1

t=96

Analysis: Continuum formulation

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dcz

dpppp

pppp

dcx

dpppp

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Fz

pww

z

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wnt

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unt

wnzt

n

''

][

1

][

1

0

CONTINUM

FIELD

FLUID

W

t=48 t=96

t=48 t=96t=72

Only the sub-harmonic is “really” nutating:effective St have diminished; L has increased

t=96, St=0.6 t=96, St=1

momentum depletion region

accumulation region

II- Outline: Particle Transport under 2-way Coupling

Computational parameters

Particle accumulation patterns

Fundamental mode saturation & pairing

Particle Statistics

1. Generation of small scales

2. Evolution of average modal stress

3. Mean kinetic energy balance

St=1

St=0.3

St=0.6

M=0.2t=72

St=0.3M=0

M=0.5M=0.2

St=1t=96

St=2M=0.2

No new instability forms for low M and uniformly distributed particles: rather drag effect

t=72 t=96

St=1, time=72

M=0

M=0.2 M=0.5

M=0.1

M=0

M=0.5M=0.2

M=0.1

St=1, time=96

t=48 t=96

Centrifuging effect of KH is lower in 2-way coupling

t=48 t=96

St=0.3 St=1

Summary

Particle transport in turbulent mixing layers was analyzed using DNS + Lagrangian particle tracking.

Particles modify the flow evolution dramatically even at mass loadings of 0.5; generation of small scales.

Intricate undulating patterns are formed.

Effect of preferential concentration on particle statistics was emphasized.

Related publications

Related publications

Narayanan C., Lakehal, D.: DNS of particle-laden mixing-layers. Part I: One-way coupled flow and dispersed-phase features. Phys. Fluids, 18(9), pp. 15, 2006.

Narayanan C., Lakehal, D.: DNS of particle-laden mixing-layers. Part II: Two-way coupled induced generation of small-scale vorticity, Phys. Fluids, 18(9), 2006.

Botto L., Narayanan C., Fulgosi M., Lakehal D.: Effect of near-wall turbulence enhancement on the mechanism of particle deposition, Int. J. Multiphase Flow, 31(8), 2005.

Lakehal D., Narayanan C.: Numerical Analysis of the continuum formulation for the Initial Evolution of Mixing Layers with Particles, Int. J. Multiphase Flow, 29(6), 2003. 

Narayanan C., Lakehal D., Botto L., Soldati A.: Mechanisms of particle deposition in a fully-developed turbulent open channel flow, Phys. of Fluids, 15(3), pp. 763, (2003).

Narayanan C., Lakehal D.: Temporal instabilities of a mixing-layer with uniform and non-uniform particle loadings, Physics of Fluids, 14(11), pp. 3775, (2002).

Narayanan C., Lakehal D.: Linear Stabilities Analysis of Particle-Laden Mixing Layers using Lagrangian Particle Tracking, Powder Technology, 125, pp. 122,  (2002).