LM-MHD Simulation Development and Recent Results Presented by Sergey Smolentsev (UCLA) with...
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Transcript of LM-MHD Simulation Development and Recent Results Presented by Sergey Smolentsev (UCLA) with...
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, 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.
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
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 MEETINGTITLE 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
UCLA
poster
LM-MHD experiments and PbLi loop progress
K. Messadek
UCLA
oral
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 expectedto be hydrodynamically unstable andeventually 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
Tendency to quasi-two-dimensional state as Ha number is increased has been demonstrated for both velocity and temperature field
Ha=100 Ha=400 Ha=700 Ha=1000
B-fie
ld
g g g
B-fie
ld B-fie
ld
Re=10,000Gr=107
a/b=1
3D modeling of MC flows
• 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
Velocity
Temperature
Ha=400 Ha=700 Ha=1000
Ha=400 Ha=700 Ha=1000
MC: comparison between 3D and 1D
Ha=400 Ha=700 Ha=1000
Fu
lly d
evelop
ed
1D analytical solution-Flow is Q2D-Flow is fully developed
Major assumptions of the 1D theoryhave been verified with 3D modeling. 1D/3D comparison is fair
Qu
asi-
2D
Full solution Wall functions BC Wall functions BC
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 H artm ann num ber
Re
yno
lds
nu
mb
er
Mo
lten
sal
t se
lf-c
oo
led
HCLL, ITER TBM
PbLi self-cooled
DCLL, ITER TBM
DC
LL
, DE
MO
OB
DC
LL
, DE
MO
IB
Li s
elf-
co
ole
d
TURBULENT FLOW
LAMINAR orQ2D TURBULENT FLOW
10 1 10 2 10 3 10 4 10 5
10 8
10 7
10 6
10 5
10 4
10 3
10 2
10 1
MHD turbulence, instability and transitions
•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
Internal shear layers
Side layer
The next few movies will illustrate major findings, namely:Type I
Type II
Direct Numerical Simulation of Q2D MHD turbulence
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
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 blanketwith FCI and helium channels
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.
Two overlapping FCI sections
Modeling FCI experiment in China
Picture of experimental MHD facilities in the Southerstern Institute of Physics (SWIP), China.
1000 mm
Flow of InGaSn in a SS rectangular duct with ideally insulating FCI made of epoxysubject to a strong (2 T) transverse magnetic field
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
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 0.002
•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 conditionsusing the fully developed flow model first (2009) and then in 3D (2010) using HIMAG
Modeling FCI experiment in China
2D modeling, previous
3D modeling, NEW !
In this figure jx (axial current) is plotted:1 – axial current in the gap, just above the slot2 – return current
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
1
2
These suggest 3D axial currents
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).
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.