Multi Scale Physics

Amazing what we can simulate and measure

Harry E.A. Van den Akker

Dept. of Multi-Scale Physics

Faculty of Applied Sciences

Delft University of Technology

Delft, The Netherlands

h.e.a.vandenakker@tudelft.nl

Multi Scale Physics

Dept. of Multi-Scale Physics

works on

Industrial & Environmental Processes

with a focus on

• Multi-Phase Flows• Reacting Flows• Environmental Flows

Multi Scale Physics

Dept. of Multi-Scale Physics

• New Numerical Toolsefficient solvers, parallel computing,

lattice-Boltzmann, Monte Carlo. ….

• New Experimental Toolsnon-intrusive diagnostics: lasers (LDA, LIF, PIV)

& radiation techniques (gamma, X-ray)

• Applications of Industrial & Societal Interest

Multi Scale Physics

Industrial Processes & Process Equipment:

stirring, mixing, blending,

suspending solids, dissolving particles,

bubbling gases, dispersing immiscible liquids,

precipitation, crystallization, chemical reactors,

(slurry) bubble columns,

2-phase / 3-phase pipelines and risers

Dept. of Multi-Scale Physics

Multi Scale Physics

CFD options available

Reynolds-Averaged Navier-Stokes simulations (RANS)

Direct Numerical Solutions (DNS) Large Eddy Simulations (LES)

Van den Akker H.E.A., Adv. Chem. Eng., Vol. 31, 151- 229, Elsevier (2006)

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Spatial distributions of bubble size according to Bakker (1992)

Rushton Lightnin A315 Pitched Blade

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Gas Fraction

%

2.0

4.0

0.0

RNG k - k -

• 3-D transient (FLUENT)

• grid: 35 x 45 x 8

• Tk - = 39 s ; TRNG k - = 27 s

• vortices move downwards

CFD Bubble Plume (TFM) Loncle, Mudde & Van den Akker (2000)

Multi Scale Physics

Reynolds Averaged Navier-Stokes (RANS) Simulations

• RANS is only suitable for the design of processes the performance of which

depends mainly on the mean flow characteristics and is not strongly affected by the turbulence

• RANS substantially underestimates turbulence levels

Montante et al. (2001)

Multi Scale Physics

A Direct Numerical Solution (DNS) resolves the flow field completely: NO MODELLING AT ALL

Limitation: Reynolds number has to be relatively low

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transient flow in a Kenics®

static mixer

Re=1000

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Comparison FLUENT (FV) with in-house LB code at Re=500

Multi Scale Physics

Comparison LB and FLUENT FV

Re = 500 (laminar, unsteady) flow in

Kenics® Static Mixer

• LB

• 7800k nodes• 1600 MB used, 4 CPUs• 12h

• FLUENT FV • 700k cells

• 660 MB used, 4 CPUs• 62h

Van Wageningen et al., European Mixing XI, Bamberg, 2003

Multi Scale Physics

Kramers Laboratorium voor Fysische Technologie

Simulations &PIVRe = 32

1.000.930.860.790.710.640.570.500.430.360.290.210.140.070.00

|v|vff|/v|/vss

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/av

12

0.012

0.4

5 vol. % particles in isotropic turbulence

Ten Cate, PhD thesis TU Delft, 2002

LB – DNSin a periodic box

Multi Scale Physics

LDA RANS (k-ε)

r/T (-)

z/T

(-)

k/vtip2

0.5 vtip

0 0.50

0.33

0.66

1

Assessment stirred tank flow, Re = 7,300

Angle-averaged flow fields

Hartmann et al. (2004), Chem. Eng. Sci. 59, 2419

LES

Multi Scale Physics

Assessment stirred tank flow, Re = 7,300

Hartmann et al. (2004), Chem. Eng. Sci. 59, 2419

k/vtip2

LDA

r/T (-)

z/T

(-)

0 0.330.26

0.4

RANS (k-ε)

Angle-resolved flow fields

LES

Multi Scale Physics

Dissolving calciumchloride beads in water

spatial particle distribution: 0 < Nt 60

dp / dp0

1

00.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9Nt

= 2

Nt

= 5

Nt

= 7

Nt

= 1

0N

t =

20

particles are 5 times enlarged

dp0 = 0.3 mm; N = 7·106

Multi Scale PhysicsLDPE reactor

Multi Scale Physics

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Conclusions (1)

RANS simulations for single-phase flows and Two-Fluid simulations for two-phase flows

have limited value

and provide limited insight only (if any)

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Conclusions (2)

LES are (becoming) feasible

and should be applied

for reproducing and improving

physical and chemical processes in

industrial an environmental flows

to allow a quantum leap

in improving processes and plants.