LM-MHD Simulation
Development and Recent
Results
Presented by Sergey Smolentsev (UCLA)
with contribution from:
R. Munipalli, P. Huang (HyPerComp)
M. Abdou, N. Morley, K. Messadek, N. Vetcha, D. Sutevski (UCLA)
R. Moreau (SIMAP, France)
Z. Xu (SWIP, China)
MHD and heat/mass transfer considerations are
primary drivers of any liquid metal blanket design
• The motion of electrically conducting
breeder/coolant in strong, plasmaconfining, magnetic field induces
electric currents, which in turn interact
with the magnetic field, resulting in
Lorentz forces that modify the original
flow in many ways. This is a subject of
magnetohydrodynamics (MHD).
• For decades, blankets were designed
using simplified MHD flow models (slug
flow, core flow approximation, etc.). The
main focus was on MHD pressure drop.
• Recent blanket studies have shown that
the MHD phenomena in blankets are
much richer and very complex (e.g.,
turbulence, coupling with heat and
mass transfer, etc.) and need much
more sophisticated analyses.
MHD Thermofluid issues of LM blankets
MHD related issue / phenomena
S-C
DCLL
HCLL
1. MHD pressure drop
***
**
**
2. Electrical insulation
***
**
*
3. Flow in a non-uniform magnetic field
***
***
**
4. Buoyant flows
**
***
***
5. MHD instabilities and turbulence
***
***
*
6. Complex geometry flow and flow balancing
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***
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7. Electromagnetic coupling
***
**
***
*
***
*
***
***
*
8. Thermal insulation
9. Interfacial phenomena
*- not applicable or low importance; ** - important; *** - very important
Where we are on MHD modeling for fusion?
• No commercial MHD CFD codes
• Modification of existing CFD codes (Fluent,
Flow3D, OpenFoam) – no significant progress yet,
results are often obviously wrong
• Many 2D, Q2D and 3D research codes – still limited
to simple geometries; other restrictions
• Development of specialized MHD codes for
blanket applications (e.g. HIMAG) – good progress
but there is a need for further improvement to achieve
blanket relevant conditions: Ha~104, Gr~1012
MHD modeling and code
development at UCLA/HyPerComp
• HIMAG (along with HYPERCOMP) –
ongoing work on development of 3D MHD
parallel MHD software for LM blanket
applications
• 2D, Q2D and 3D research codes to
address particular MHD flows under
blanket relevant conditions
In this presentation:
• New modeling results for “mixed convection” in poloidal flows
• Study of hydrodynamic instabilities and transitions in MHD flows with
“M-shaped” velocity profile
• 3D modeling of Flow Channel Insert (FCI) experiment in China
OTHER RELATED PRESENTATIONS at THIS MEETING
TITLE
Presenter
Oral/Poster
3D HIMAG development progress
R. Munipalli
HyPerComp
oral
Study of MHD mixed convection in
poloidal flows of DCLL blanket
N. Vetcha
UCLA
poster
D. Sutevski
UCLA
poster
K. Messadek
UCLA
oral
Modeling China FCI experiment
LM-MHD experiments and PbLi loop
progress
Mixed Convection (MC)
• In poloidal ducts, volumetric heating
causes strong Archimedes forces in PbLi,
resulting in buoyant flows
• Forced flow ~ 10 cm/s
Buoyant flow ~ 30 cm/s
• MC affects the temperature field in the FCI,
interfacial temperature, heat losses and
tritium transport – all IMPORTANT!
In the DCLL blanket conditions,
the poloidal flows are expected
to be hydrodynamically unstable and
eventually turbulent
How we attack the MC problem
• Full 3D computations using HIMAG: limited to
Ha~1000, Re~10,000, Gr~10^7; the code does
not reproduce turbulence
• Spectral Q2D MHD code (UCLA, Smolentsev):
captures MHD turbulence but limited to simplified
geometry and periodic BC
• 1D analytical solution for undisturbed flow
• Linear stability analysis to predict transitions in
the flow – see poster presentation by N. Vetcha
• Experiment – see presentation by K. Messadek
3D modeling of MC flows
Ha=700
Ha=400
Ha=100
Ha=1000
Re=10,000
Gr=107
a/b=1
g
g
g
Tendency to quasi-two-dimensional state as Ha number is increased has
been demonstrated for both velocity and temperature field
3D modeling of MC flows
Velocity
Ha=400
Ha=700
Temperature
Ha=400
Ha=700
• Pronounced entry/exit
effects
Ha=1000 • Reverse flow bubble at
the entry
• Accelerated flow zone
at the entry
• “Hot” spot in the left-top
corner
• Reduction of entry/exit
effects with B
Ha=1000
• Near fully developed
flow in the middle
MC: comparison between 3D and 1D
Full solution
Ha=400
Wall functions BC
Ha=700
Wall functions BC
Ha=1000
Fully developed
1D analytical solution
-Flow is Q2D
-Flow is fully developed
Major assumptions of the 1D theory
have been verified with 3D modeling.
1D/3D comparison is fair
MHD turbulence, instability and transitions
M o lte n s a lt s e lf-c o o le d
105
D C L L , IT E R T B M
104
103
H C L L , IT E R T B M
10
2
L A M IN A R o r
Q 2D TURBULENT FLO W
101
101
•
The Q2D turbulent structures
appear as large columnar-like
vortices aligned with the field
direction. This Q2D MHD
turbulence is mostly foreseen in
long poloidal ducts resulting in a
strong modification of heat and
mass transfer.
•
We do some analysis for MHD
instability and laminar-turbulent
transitions for flows with “Mshaped” velocity profiles, which
are typical to blanket conditions
P b L i s e lf-c o o le d
L i s e lf-c o o le d
106
DCLL, DEM O OB
R e y n o ld s n u m b e r
107
All liquid metal blankets fall on the
sub-region below the line
Re/Ha~200 associated with the
turbulization of the Hartmann
layer. Here, MHD turbulence
exists in a very specific quasi-twodimensional (Q2D) form.
TURBULENT FLOW
D C L L , D E M O IB
108
•
102
103
104
H a rtm a n n n u m b e r
105
MHD turbulence, instability and transitions
Direct Numerical Simulation of Q2D MHD turbulence
Side layer
Internal
shear layers
The next few movies will illustrate
major findings, namely:
Type I
Type II
•How the instability starts
•Two types of instability
•Primarily instability (Type I):
inflectional instability
•Secondary instability (Type II):
bulk eddy/wall interaction
•How MHD turbulence eventually evolves
MHD turbulence, instability and transitions
Type I (primarily) instability (Re=2500, Ha=200)
Transition from Type I to Type II instability and evolvement of MHD turbulence
Modeling FCI experiment in China
M.S. TILLACK, S. MALANG, “High Performance PbLi Blanket,”
Proc.17th IEE/NPSS Symposium on Fusion Engineering, Vol.2,
1000-1004, San Diego, California, Oct.6-10, 1997.

Sic/SiC FCI is used inside the DCLL blanket and also in the
feeding ducts as electrical and thermal insulator allowing for
ΔP<2 MPa, T~700 C, >40%

Possible thermal deformations and small FCI displacements are
accommodated with a ~ 2-mm gap also filled with PbLi

Tritium and corrosion products in the gap are removed with the
slowly flowing PbLi

There are pressure equalization openings in the FCI, either in the
form of holes (PEH) or a single slot (PES), to equalize the
pressure between the gap and the bulk flow

The FCI surfaces are sealed with CVD-SiC to prevent “soaking”
PbLi. The sealing layer can also serve as a tritium permeation
barrier

The FCI is subdivided into sections, each about 0.25-0.5 m long.
Two FCI sections are loosely overlapped at the junction, similar to
roof tiles

The FCI is thought as a purely functional (not a structural)
element experiencing only secondary stresses, which can be
tolerated
Poloidal duct of the DCLL blanket
with FCI and helium channels
Two overlapping FCI sections
Modeling FCI experiment in China
Flow of InGaSn in a SS rectangular duct with ideally insulating FCI made of epoxy
subject to a strong (2 T) transverse magnetic field
1000 mm
Picture of experimental MHD facilities in the
Southerstern Institute of Physics (SWIP), China.
Courtesy of Prof. Zengyu XU, SWIP
Modeling FCI experiment in China
Dimension
Notation
Value, m
Half-width of the FCI box
b
0.023
Half-height of the FCI box
a
0.027
tFCI
0.002
Thickness of the gap
tg
0.005
Thickness of the slot
ts
0.003
Thickness of the Fe wall
tw
0.002
FCI thickness
•2 mm FCI made of epoxy provides ideal electrical insulation
•Maximum magnetic field is 2 T (Ha=2400)
•Uniform B-field: 740 mm (length) x 170 mm (width) x 80 mm (height)
•Outer SS rectangular duct: 1500 mm long
•FCI box: 1000 mm long
•Pressure equalization openings: slot (PES) or holes (PES)
•Measurements: pressure drop, velocity (LEVI)
Modeling was performed under the experimental conditions
using the fully developed flow model first (2009) and then
in 3D (2010) using HIMAG
Modeling FCI experiment in China
S. SMOLENTSEV, Z.XU, C.PAN, M.ABDOU, Numerical and
Experimental Studies of MHD flow in a Rectangular Duct with a
Non-Conducting Flow Insert, Magnetohydrodynamics, 46, 99-111
(2010).
Pressure drop coefficient
Previous 2D computations show
MHD pressure drop much smaller
than that in the experiment
Current 3D computations demonstrate
good match with the experiment
These suggest 3D axial currents
3D modeling, NEW !
2D modeling, previous
1
2
In this figure jx (axial current) is plotted:
1 – axial current in the gap, just above the slot
2 – return current
Concluding remarks
• In the recent past, the main focus of MHD studies for fusion
applications was placed mostly on MHD pressure drop.
• Although MHD pressure drop still remains one of the most important
issues, current studies are more focusing on the detailed structure of
MHD flows in the blanket, including various 3D and unsteady
effects.
• These phenomena are not fully understood yet. For example, the
mass transport (e.g. tritium permeation, corrosion) is closely coupled
with MHD flows and heat transfer, requiring much better knowledge
compared to relatively simple pressure drop predictions.
• Therefore, the key to the development of advanced liquid metal
blankets for future power plants lies in a better understanding of
complex MHD flows, both laminar and turbulent, via developing
validated numerical tools and physical experiments.