1. 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)

2. MHD and heat/mass transfer considerations are primary drivers of any liquid metal blanket design
The motion of electrically conducting breeder/coolant in strong, plasma- confining, 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.

3. 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
7. Electromagnetic coupling
8. Thermal insulation
9. Interfacial phenomena
*- not applicable or low importance; ** - important; *** - very important

4. 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

5. 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

6. In this presentation: OTHER RELATED PRESENTATIONS at THIS MEETING
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
Modeling China FCI experiment
D. Sutevski
LM-MHD experiments and PbLi loop progress
K. Messadek

7. 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

8. 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

9. 3D modeling of MC flows g g g Ha=100 Ha=400 Ha=700 Ha=1000 Re=10,000
Gr=107
a/b=1
B-field
B-field
B-field g g g
Tendency to quasi-two-dimensional state as Ha number is increased has been demonstrated for both velocity and temperature field

10. 3D modeling of MC flows Pronounced entry/exit effects
Velocity
Pronounced entry/exit effects
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
Near fully developed flow in the middle
Ha=400
Ha=700
Ha=1000
Temperature
Ha=400
Ha=700
Ha=1000

11. MC: comparison between 3D and 1D
Full solution
Wall functions BC
Wall functions BC
Ha=400
Ha=700
Ha=1000
1D analytical solution
Flow is Q2D
Flow is fully developed
Fully developed
Quasi-2D
Major assumptions of the 1D theory
have been verified with 3D modeling.
1D/3D comparison is fair

12. MHD turbulence, instability and transitions
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-two-dimensional (Q2D) form.
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 “M-shaped” velocity profiles, which are typical to blanket conditions

13. MHD turbulence, instability and transitions
Direct Numerical Simulation of Q2D MHD turbulence
Internal shear layers
Side layer
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

14. 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

15. Modeling FCI experiment in China
M.S. TILLACK, S. MALANG, “High Performance PbLi Blanket,” Proc.17th IEE/NPSS Symposium on Fusion Engineering, Vol.2, , San Diego, California, Oct.6-10, 1997.
Poloidal duct of the DCLL blanket
with FCI and helium channels
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 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
Two overlapping FCI sections

16. 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
Picture of experimental MHD facilities in the Southerstern Institute of Physics (SWIP), China.
1000 mm
Courtesy of Prof. Zengyu XU, SWIP

17. 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
FCI thickness
tFCI
0.002
Thickness of the gap tg
0.005
Thickness of the slot ts
0.003
Thickness of the Fe wall tw
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

18. 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, (2010).
Previous 2D computations show
MHD pressure drop much smaller
than that in the experiment
Pressure drop coefficient
2D modeling, previous
3D modeling, NEW !
Current 3D computations demonstrate
good match with the experiment
These suggest 3D axial currents 1 2
In this figure jx (axial current) is plotted:
1 – axial current in the gap, just above the slot
2 – return current

19. 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.

20. Thank you for your time