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Application of the Immersed Boundary Method to particle-laden andp
bubbly flows
T. Kempe, B. Vowinckel, S. Schwarz, C. Santarelli, J. Fröhlich
Institute of Fluid MechanicsInstitute of Fluid MechanicsTU Dresden, Germany
EUROMECH Colloquium 549, Leiden, 17-19 June 2013
Motivation - Particles
[J. Gaffney, University of Minnesota, www.youtube.com]
http://ryanhanrahan.wordpress.com
Bed load transport
Important for multiple applications
Fundamental research
2T. Kempe
Motivation - Particles
Experiments at University of Aberdeen in progress
Our goal:Our goal:
Analysis by direct numerical simulations
Later: comparison with experimentsLater: comparison with experiments
3T. Kempe
Motivation - Bubbles
Our goals:
Bubble - turbulence interactionBubble turbulence interaction
Bubbles in MHD flows
Formation of metal foamsFormation of metal foams
X R • X-Ray measurements [Boden EPM 2009]
• Ar in GaInSn • Ar in GaInSn • No magnetic field
4T. Kempe
PRIME(Phase-Resolving sIMulation Environment)
Solver for continuous phaseIncompressible Navier-Stokes equations
( ) fuuuu+∇=∇+⋅∇+
∂ 21 νp
S
2nd order Finite Volumes
( ) fuuu +∇∇+∇+∂
νρ
pt
8
Staggered Cartesian grid
Explicit 3-step Runge-Kutta for convective terms
Speedup with 2.65·108 grid pointssolid: ideal , dash-dot: PRIME
p p gImplicit Crank-Nicolson for diffusive terms
Highly sophisticated libraries
E
g y pPETSc for parallelization (MPI)HYPRE as solver (Poisson, Helmholtz Eq.)
6
Scaleup with 1.3·105 grid points per processor
T. Kempe
Immersed boundary method [Uhlmann JCP 2005]
Fluid solved on fixed Cartesian gridFluid-solid interface represented by markersPhase coupling by volume forcesPhase coupling by volume forces
Interpolation of velocities to marker pointsDirect forcing d −
=ΓUUF
Spreading to grid points Regularized δ – functions used F
f
tΔF
Grid points and surface markersRegularized δ – function[ Roma, 1999]
P tiPropertiesgood stability order of convergence
L2 - error of velocity,single sphere in
channel flow
1st Order
2nd O d
7
≈1.7 2nd Order
T. Kempe
Mobile particles[Uhlmann JCP 2005]
[Kempe & Fröhlich JCP 2012]
Linear momentum balance:
ud
[Kempe & Fröhlich JCP 2012]
cpfpfp
p VSt
m Fgnτu
+−+⋅= ∫Γ
)( dd
dρρρ Collisions
Angular momentum balance:
Pressure & viscous forces buoyancySphere with 874 marker points
g
cfp
c St
I Mnτrω
+⋅×= ∫ d)(d
dρ
Runge–Kutta (3rd order) for time integration
t Γd
Parallel implementation in PRIME
Master & slave strategy Particle with interface resolution in
8
Master & slave strategy Particle with interface resolution in decomposed domain
T. Kempe
Improved IBM
gfu
+−
−= ∫p
VVt fpp
fp
Ωρρρ
d)(d
d
8
( )
∑
∑
=
=
−−≈ 8
1
8
1,,
mm
mmm
kji
H
φ
φφα
R
Velocity u at Ly /2, Re=10
Stable time integration for previously g p yinaccessible density ratiosAccurate imposition of BC’s
9
Velocity of buoyant & sedimenting particles
[Kempe & Fröhlich, JCP , 2012]
T. Kempe
Normal particle-wall collision with various collision modelsvarious collision models
up
soft-sphere model
repulsive potential, kn=1e6
Repulsive potential
Hard-sphere model
experiment
repulsive potential, kn=1e4
Soft-sphere model
Choice of coefficients ?
Time scale separation for
Surface distance vs. time
hard-sphere model
p
fluid and collision
Δt100≈
Δ
Δ
c
f
tt
M d l bl f l l i l i
11
Models not usable for large-scale simulations
T. Kempe
Adaptive collision time model (ACTM)
Purpose Avoid reduction of Δ tf
Give correct restitution ratio in
outdry u
ue =
Ideas Stretch collision in time to Tc = 10 Δ tf
Optimization to find coefficients
in
ODE of collision process
dd2 ζζ ζ0
dd
dd 2/3
2
2
=++ nnn
nn
p kt
dt
m ζζζ Physically exact
ACTM
ζ
Problem: given : uin , edry , Tc
find : dn , kn
rp0
Fixed-point problem solved by Quasi-Newton scheme
tTc
Quasi Newton scheme
12T. Kempe
linear approaches possible [Breugem 2010]
Oblique collisions
Oblique = normal + tangential
Normal ACTM
q
[Joseph 2004]
Normal ACTM
Tangential force model (ATFM)
Consider only sliding and rolling Consider only sliding and rolling
Critical local impact angle
Sliding: Coulomb friction
RSΨ cpinn
cpint
in gg
,
,=Ψ
Sliding: Coulomb friction
Rolling: Compute force such that relative
nfcol
t FF μ=
Rolling: Compute force such that relative
surface velocity is zero 0=cptg
( )( )( ) tF 2
,,,,
2 ppp
intq
intpp
intq
intpppcol
t RmItRuumI
+Δ
+−−=
ωω
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Lubrication modeling
Local grid refinement not desiredUnder-resolved fluid in gap
[Gondret, 2002]with lubrication model
without model
explicit expression for lubrication force [Cox & Brenner , 1967]
without model
1
2
6 −
⎟⎟⎠
⎞⎜⎜⎝
⎛
+−= n
qp
qpnf
lubn RR
RRgF ζμπ
Particle-wall collision, St = 27⎠⎝ qp
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Resolved and modeled contributions during a particle-wall collision
T. Kempe
Adaptive collision model (ACM)Adaptive collision model (ACM)
Phase 1 Phase 2 Phase 3Phase 1 Phase 2 Phase 3
Up,out
Up,in
Approach Surface contact Rebound
Lubrication model Normal ACTMTangential ATFM
Lubrication model
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Normal collisions – Results [Kempe & Fröhlich JFM 2012]
edry = 0
present Experiment
edry = 0.97
present
[Gondret, 2002]
Steel spheres impacting on glass wall
Flow around sphere impacting on wall,Left: simulation, right: experiment [Eames, 2000]
Fluid time step can be used pppp DuSt
ρτFluid time step can be usedLocal grid refinement is avoidedGood agreement with experiments
f
ppp
f
pStμτ 9
==
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Effective angle of impact
Oblique collisions – Results [Kempe & Fröhlich JFM 2012]
Effective angle of impact
Effective angle of rebound
cpinn
cpint
in gg
,
,=Ψ
Effective angle of rebound
cpinn
cpoutt
out gg
,
,=Ψcp
outtgcp
inng ,cp
intg ,
Compared with experiment [Joseph, 2004]
Glass spheres, rough, μ f = 0.15Steel spheres, smooth, μ f = 0.01
outtg ,
Glass spheres, rough, μ f 0.15ΨRS = 0.95
present
p μ f ΨRS = 0.25
sliding
ΨRS
rolling
Ψ
17T. Kempe
Stretched collisions with multiple particles
Results with static stiffness
EFluid
Ekin
Significant influence of Δt
Results with ACM
Fi l ti l iti Etotal /20
Final particle positions
EFluid
Ekin
1818T. Kempe
CFL = 1 (stretched) CFL = 0.02 (Hertz)
Results independent of Δt
3D interface resolved
Short history „DNS of sediment transport“
Uhlmann & Fröhlich 2006
3D, interface resolved18 million fluid points560 particles, short runs, no statistics
Osanloo 20082D, mass pointsFixed velocity profile for fluid
Papista 2011
y p
2D, interface resolved200 i l200 particles
3D, interface resolved
Vowinckel 2012
,645 million fluid points8696 particles
This project
3D, interface resolved1.4 billion fluid points40500 pa ticles40500 particles
20T. Kempe
Computational Setup
H/D Lx/H Lz/H Reb Reτ D+
9 24 6 2941 193 21
Two layers of particles:
• Fixed bed: single layer of hexagonal packing
• Sediment bed on top
Free slipp
No slip
Periodic in x- and z- direction 21T. Kempe
Numerics
Nx Ny Nz Ntot D/Δx Δx+ Nproc
4800 240 1200 1.4·109 22.2 0.95 4048 - 16192
true DNS all scales resolved
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Computational Setup
Case Np,fixed Np,mobil Θ /Θcrit Configuration
Fix 27000 0 0 Two fixed layers
Ref 13500 13500 1.18 One layer of mobile particles
FewPart 13500 6750 1.18 Lower mass loading
LowSh 13500 13500 0.75 Lower mobility
( )gDu
p ρρρ
θ τ
−=
2
Mobility Shields parameter( )gp ρρ
Probability
TransitionalSmooth
θ
of particlemotion
D+f
Rough
DRef,FewPart
LowSh
23T. Kempe
Case Ref Θ /Θcrit = 1.18 [Vowinckel et al. ICMF 2013]
Spanwise oriented dunes
Contour Iso-surfaces of fluctuations Particleu / Uu / Ub
u' / Ub = -0.3' / U 0 3
up / uτ ≥ 4up / uτ< 4fixedu' / Ub = 0.30
24T. Kempe
Case Ref Θ /Θcrit = 1.18
mean fluid velocity <u> fluctuations <u’ u’>
0.8
1
Fix
0.8
1
mean fluid velocity <u>
0.8
1y
/ H
-0.2
0
0.2
0.4
0.6
0.8 FixRefFewPartLowSh
y / H
0.2
0.4
0.6
y / H
0.2
0.4
0.6
<u> / Ub
0 0.5 1-0.2
Mobile or restingFixed bed
<u> / U0 0.5 1
-0.2
0
0.2
<u’u’> / U20 0.02 0.04 0.06-0.2
0
0.2
<u> / Ub<u’u’> / Ub
higher intrusion, larger resistance, more turbulence25T. Kempe
Less particles Θ /Θcrit = 1.18
Streamwise oriented, inactive ridges
Contour Iso-surfaces of fluctuations Particleu / U
u' / Ub = -0.3' / U 0 3
up / uτ ≥ 4up / uτ< 4
u / Ub
fixedu' / Ub = 0.30
26T. Kempe
Heavier particles Θ /Θcrit = 0.75
Inactive plane bed with single eroded particles
Contour Iso-surfaces of fluctuations Particleu / U
u' / Ub = -0.3' / U 0 3
up / uτ ≥ 4up / uτ< 4
u / Ub
fixedu' / Ub = 0.30
28T. Kempe
Conclusions so far [Vowinckel et al. ICMF 2013]
many & light particles:
Two parameters: mass loading & mobility (=density)
y g p
dunes with distance 12H
few & light :
inactive ridges
many & heavy :
closed plane bed
Experiments [Dietrich et al. Nature 1989]
Sediment patterns in agreement with experimental evidence29T. Kempe
Bubble shape depends on regime
Reynolds number
[Clift et al. 1978]
number
νeqpdu
=Reν
ρρ 2dg
Eötvös numberσρρ eqfp dg
Eo−
=
31T. Kempe
Representation of bubble shapes
• Spherical Particles as model for bubbles
• Ellipsoidal
time dependent shape X(t)baX =b
a
• Spherical harmonics
∑+= mnmn Ytaatr 0 ),()(),,( θφθφ
Exact evaluation of curvature, normal vector, volume…
∑mn
nmn,
0 ),()(),,( φφ
[Bagha 1981]Coupling of shape to fluid loads by local force blance (vanishing displacement energy)
32T. Kempe
[Schwarz & Fröhlich ICNAAM 2012]
Light particles in vertical turbulent channel flow
Upward flow
• lenght x height x width = 2 2H x H x 1 1H• lenght x height x width 2.2H x H x 1.1H
• periodic in x- und z- direction
• Wall: no-slip
• Fluid Reynolds number
• Mesh
for unladen flow
33T. Kempe
Particle parameters
Fixed shape:
oblate ellipsoid
0 001ρp
Density ratio: 0.001ρf
Density ratio:
Np Deq/H Deq/∆ a/b Void fr. Rep
740 0.05172 ~24 2 ~ 2 % ~214
34T. Kempe
Looking atLooking at
transport of particles by the flow
influence of particles on turbulence
particle-particle interaction
[Santarelli ICMF 2013]
35T. Kempe
Results: fluid phase
mean streamwise velocity turbulent kinetic energy
Symmetry loss and turbulence enhancement
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Ascent of single bubble in liquid metal [Schwarz 2013]
Argon bubble deq = 4.6 mm in quiescent GaInSn: Eo = 2.5Experiments by [Zhang et al. 2005]
− Cartesian grid: 84 Mio. Pointsg− 9093 Lagrangian surface
markers− “Wobbling” bubble shape
Re Ret
− 60 x 61.5 CPU hours
PRI• Comparison
Unsteady rise velocity, ellipsoidal
0.270.28f / 245369σRe
2871
2879
MEAveraged rise velocity matches exp. dataUnderprediction of standard deviation in ReGood agreement in oscillation frequency0.27
60.28
0f / fref
245369σRe[Schwarz, 2011, 2013]
37T. Kempe
Single bubble in liquid metal with vertical magnetic field
dB 2
ref
eqel
udB
Nρ
σ 20=)( Bjf ×= NL )( Buj ×+Φ−∇= eσ 0=⋅∇ j
)(2 Bu×⋅∇=Φ∇
electric current density jj
)( Bu×⋅∇=Φ∇
By
By
electric potentialjelectric conductivity jeσ
Φ
More rectilinear bubbletrajectory
R d d ill tiReduced oscillationfrequency & amplitude in Re
Large bubbles rise faster, small ones slower
Ny = 0 Ny = 1
small ones slower
Reduced wake vorticity with larger vortices being alignedwith B
Instant. helicity iso-contours
38
with B
Ny = 0 Ny = 1T. Kempe [Schwarz 2013]