21st CENTURY FRONTIERS
Moving Beyond Prediction to Control
Free Surface, Turbulence, and Magnetohydrodynamics:
Interactions and effects on
flow control and interfacial transport
Mohamed Abdou
Professor, Mechanical & Aerospace Engineering, UCLA
First International Symposium on Free Surface Flow and
Interfacial Transport Phenomena
Yugawara, Atami, Japan - May 10-11, 2001
Illustration of Liquid Walls
Fast Flow FW
Thin Liquid Wall
- Thin (1-2 cm) of
liquid flowing on
the plasma-side of
First Wall
Thick Liquid
Blanket
Vacuum Vessel
Thick Liquid Wall
- Fast moving liquid
as first wall
- Slowly moving
thick liquid as the
blanket
Motivation for Liquid Wall Research
What may be realized if we can develop good liquid walls:
 Improvements in Plasma Stability and Confinement
Enable high β, stable physics regimes if liquid metals are used
 High Power Density Capability
 Increased Potential for Disruption Survivability
 Reduced Volume of Radioactive Waste
 Reduced Radiation Damage in Structural Materials
-Makes difficult structural materials problems more tractable
 Potential for Higher Availability
-Increased lifetime and reduced failure rates
-Faster maintenance
No single LW concept may simultaneously realize all these benefits, but
realizing even a subset will be remarkable progress for fusion
“Liquid Walls” Emerged in APEX as one of the Two
Most Promising Classes of Concepts
• The Liquid Wall idea is “Concept Rich”
Fluid In
q 
r
V
rr
JJ
-+
r r
jB
Plasma
r
B
r
g
Plasma-Liquid
Interactions
Fluid Out
a) Working fluid: Liquid Metal, low
conductivity fluid
b) Liquid Thickness
- thin to remove surface heat flux
- thick to also attenuate the neutrons
c) Type of restraining force/flow control
- passive flow control (centrifugal
force)
- active flow control (applied current)
• We identified many common and many
widely different merits and issues for
these concepts
Swirling Thick Liquid Walls for High Power Density FRC
Design: Horizontally-oriented structural cylinder with
a liquid vortex flow covering the inside surface. Thick
liquid blanket interposed between plasma and all
structure
Computer Simulation: 3-D time-dependent NavierStokes Equations solved with RNG turbulence model
and Volume of Fluid algorithm for free surface tracking
Results: Adhesion and liquid thickness uniformity (> 50 cm)
met with a flow of Vaxial = 10 m/s, V,ave = 11 m/s
Calculated velocity and surface depth
ELECTROMAGNETIC FLOW CONTROL: electric current
is applied to provide adhesion of the liquid and its acceleration
Electromagnetically Restrained LM Wall
(R.Woolley)
r
r r
- Adhesion to the wall by F = J  B
r r r
F = J B
Fluid In
r r r
F = J B
-+
r
g
Inboard
r r r
F = J B
Magnetic propulsion scheme
r (L.Zakharov)
r r
Adhesion to the wall by F = Jr  B
Utilization of 1/R variation of B to drive
the liquid from the inboard to outboard
r r r
F = J B
r r r
F = J B
r
V
r
J
P2
P1

r
B
Outboard
r r r
F = J B
Fluid Out
r
B
r
V
-
Fluid Out
+
Inboard
Outboard
r r r
F = J B
r
V is driven byDP
r r r
F = J B
Magnetic Propulsion is one way to use
MHD forces to overcome drag
BZ1
BZ2
1.2
6
- no current
- with current
5
1.0
h / ho
4
3
2, 1
7
0.8
8
0.6
9
0.4
0
2
4
Innovative idea from L. Zakharov
(PPPL) where applied current is
used to induce pressure gradient
that propels flow!
6
8
10
x / ho
In calculations: L=20 cm; h0=2 cm; U0=5 m/s
• Increase of the field gradient, (BZ1BZ2)/L, results in the higher MHD
drag (blue curves 1-6)
• Applying an electric current leads to
the magnetic propulsion effect and
the flow thickness decrease (red
curves 7-9)
Scientific Issues for Liquid Walls
1. Thermofluid Issues
- Interfacial Transport and Turbulence Modifications at Free-Surface
- Hydrodynamic Control of Free-Surface Flow in Complex Geometries, including
Penetrations, Submerged Walls, Inverted Surfaces, etc.
- MHD Effects on Free-Surface Flow for Low- and High-Conductivity Fluids
2. Effects of Liquid Wall on Core Plasma
- Discharge Evolution (startup, fueling, transport, beneficial effects of low
recycling
- Plasma stability including beneficial effects of conducting shell and flow
3. Plasma-Liquid Surface Interactions
- Limits on operating temperature for liquid surface
Liquid Wall Researchers are Advancing the
Understanding of Interacting Multi-Scale Phenomena
at the Frontiers of Fluid Dynamics
Interfacial Transport
Fluid In
SCALAR
TRANSPORT
q 
-+
Plasma-Liquid
Interactions
Plasma
r
B
ELECTROMAGNETISM
r
V
rr
JJ
FREE SURFACE
PHENOMENA
r r
jB
r
g
HYDRODYNAMICS/
TURBULENCE
Fluid Out
MHD
Fusion LW Researchers are Contributing to the Resolution
of
GRAND CHALLENGES in Fluid Dynamics
Interfacial Transport
SCALAR
TRANSPORT
T r
ρC p [ + (V  )T] = kDT
t
C r
+ (V  )C = DDC
t
ELECTROMAGNETISM
r
r r
B 1 r
=
ΔB +   (V  B);
t σμ 0
r 1
r
r
j=
B B = 0
μ0
Liquid Walls:
many interacting
phenomena
•Turbulence redistributions
at free surface
FREE SURFACE
PHENOMENA
r

+ (V  ) = 0
t
•Turbulence-MHD interactions
•MHD effects on mean flow and
surface stability
•Influence of turbulence and
surface waves on interfacial
transport and surface renewal
Teraflop Computer
Simulation
MHD
HYDRODYNAMICS/
TURBULENCE
r
r
r
V
1
+ (V  )V = - p
t
ρ
r 1r r
+τ + g + jB
ρ
r
V = 0
CHALLENGE: FREE SURFACE FLOW
“Open Channel Flows
are essential to the
world as we know it” Munson, Young,
Okiishi (from their Textbook)
Free surface flow forms:
films, droplets, jets, bubbles,
etc. Fluid regions can
coalesce, break up, and
exhibit non-linear behavior
• The term free surface is often used for any
gas/void to liquid interface, but denotes an
interface between a liquid and a second
medium that is unable to support an applied
pressure gradient or shear stress.
• Formation of surface waves, a distinguishing
feature (for LW - Fr > 1, supercritical flow)
• Interfacial flows are difficult to model computational domain changes in time
making application of BCs difficult
• Interfacial tension effects make equations
“stiff”- differing time scales for surface
wave celerity compared to liquid velocity
Watermark - Shear layer instability at
water surface - CalTech Data
Numerically tracking moving interfaces is
an ongoing challenge in CFD Still NO IDEAL Interface Tracking Method
Volume-of-Fluid (VOF): The method is based on the concept of advection of a
fluid volume fraction, . It is then possible to locate surfaces, as well as determine surface
slopes and surface curvatures from the VOF data.
VOF
 t + u x + v y = 0 , 0    1
Level-Set Method: The method involves advecting a continuous scalar variable. An
interface can thus be represented by a level set of the scalar variable. This is a different
approach from VOF where the discontinuity represents the interface.
OTHERS:
Lagrangian Grid Methods
Surface Height Method
Marker-and-Cell (MAC) Method
Watermark - milk drop splash simulation
using VOF- Kunugi, Kyoto Univ.
State-of-the-Art Computational Techniques
are Required for Intensive LW Simulation
•Grid adaption or
multi-resolution
•Parallel Algorithm
Implementation
•Unstructured Meshes
•High-order advection
and free surface
tracking algorithms
Lithium Jet start-up without and with grid adaption HyperComp Simulation
CHALLENGE: TURBULENCE
•In Turbulent Motion the “various flow
quantities exhibit random spatial and
temporal variations” where “statistically
distinct average values can be discerned.”
- Hinze
Center for Computations Science and Engineering
(LBNL). LES simulation of instability in a
submerged plane jet.
Horace Lamb, British physicist:
“I am an old man now, and when I die and
go to heaven there are two matters on
which I hope for enlightenment. One is
quantum electrodynamics, and the other is
the turbulent motion of fluids. And about
the former I am rather optimistic.”
•Turbulence is the rule, not the exception,
in most practical flows. Turbulence is not
an unfortunate phenomena. Enhancing
turbulence is often the goal.
•Vastly different length and time scales
make equations stiff - requiring large
number of computational cycles. High
resolution required to capture all length
scales and geometrical complexities.
Teraflop Computers
are Making TURBULENCE Accessible
Super-computers
Averaged Models:
Some or all
fluctuation scales
are modeled in an
average sense
Teraflop computing
Turbulence Structure Simulated
DNS
length ratio: l/Re3/4
grid number: N(3Re)9/4
For Re=104 , N1010
LES
RANS
Approach
Level of description
Computational challenge
DNS
Gives all information
High.
Simple geometry, Low Re
LES
Resolves large scales.
Small scales are averaged
Moderate to high
RANS
Mean-flow level
Low to moderate.
Complex geometry possible
Turbulence / free surface interaction produces key
phenomena - anisotropic near-surface turbulence
•Turbulent production
dominated by the
generation of wall ejections,
formation of spanwise
“upsurging vortices”
•Upsurging vortices reach
free surface, form surface
deformation patches, roll
back in form of spanwise
“downswinging vortices”,
with inflow into the bulk.
Conceptual illustration of experimental observation of burst-interface
interactions - From Rashidi, Physics of Fluids, No.9, November 1997 .
Watermark - Vortex structure and free surface
deformation (DNS calculation)
•The ejection - inflow events
are associated with the
deformation of the free
surface and a redistribution
of near surface vorticity and
velocity fields.
CHALLENGE: MAGNETOHYDRODYNAMICS
ie
B-f
•Complex non-linear interactions between
fluid dynamics and electrodynamics
ld
•Powerful mechanism to “influence” fluids
•Strong drag effects, thin active boundary
layers, large (possibly reversed) velocity
jets are characteristic MHD phenomena
FLOW
•Large currents with joule dissipation and
even self-sustaining dynamo effects add to
computational complexity
Computational Challenge Li flow in a chute
in a transverse field with: b=0.1 m (halfwidth); B0=12 T (field)
Ha = B0b
Free surface flow velocity jets produced from
MHD interaction - UCLA calculation

 100,000

 Ha =
b
= 10 - 6 m
Ha
Each cross-section requires
2
10
(
b
/

)
=
10
Ha
MANY uniform grids, or special
non-uniform meshes.
MHD interactions can change the nature of
turbulence - providing a lever of CONTROL
•Applied Lorentz forces act mainly in the
fluid regions near the walls where they can
prevent flow separation or reduce friction
drag by changing the flow structure.
•Because heat and mass transfer rely
strongly on the flow structure, they can in
turn be controlled in such fashion.
Flow direction
Experimental control of flow separation by a
magnetic field:
fully developed von Kármán vortex street without
a magnetic field (upper)
with a magnetic field (right)
From Dresden University of Technology
NEW PHENOMENA IN LM-MHD FLOW
2D Turbulence
3D fluctuations on
free surface
N=0
r
B
Surface fluctuations
become nearly 2D
along field
N=6
SOME PROPERTIES OF
2-D MHD TURBULENCE:
Surface fluctuations
are nearly suppressed
B
N=10
LM free surface images with motion from left to right Latvian Academy of Science Data
Inverse energy cascade;
Large energy containing
vortices;
Low Joule and Viscous
dissipation;
Insignificant effect on the
hydraulic drag.
2-D turbulence could be
very useful as a mean of
intensifying heat transfer.
Our Science-based CFD Modeling and Experiments are
Utilized to Develop Engineering Tools for LW Applications
Joule Dissipation
DNS
0.012
for free surface MHD flows
developed as a part of collaboration between UCLA and
Japanese Profs Kunugi
and Satake
4
0.008
3
0.004
DI
D+
2
DII
0
1
K
-0.004
-0.008
0
0
40
80
120
160
y+
DNS and Experimental data are used at UCLA for
characterizing free surface MHD turbulence
phenomena and developing closures in RANS models
EXPERIMENTS
underway at UCLA for near
surface turbulence and
interfacial transport
measurements
Turbulent Prandtl number
30
K+
Extend RANS
Turbulence
Models for
MHD, Free
Surface Flows
K-epsilon
RST model
11
- Re=13 000
17 900
20 200
32 100
2
2
20
1 - Pr_t for a smooth surface
(from experimental data)
Turbulent Prandtl Number
Curve1: Available Experimental
Data
2 - Pr_t for a wavy surface (expected)
- Missing 0.95-1 and restricted to smooth
10
surface, non-MHD flows
0
0.75
0.80
0.85
0.90
y/h
0.95
1.00
Curve2: “Expected” for wavy
surface
A BIG STEP FORWARD (1st FREE SURFACE, MHD TURBULENT DNS)
Ha=0
•Strong redistribution of turbulence by a
magnetic field is seen.
•Frequency of vortex structures
decreases, but vortex size increases.
Ha=10, Spanwise
Ha=20, Streamwise
•Stronger suppresion effect occurs in a
spanwise magnetic field
•Free surface approximated as a free
slip boundary. Work proceeding on a
deformable free surface solution.
“DNS of turbulent free surface flow with MHD at
Ret = 150” - Satake, Kunugi, and Smolentsev,
Computational Fluid Dynamics Conf., Tokyo, 2000
Extending the state-of-the-art in RANS
with MHD and free surface effects
12
K
+ vj
t
2
 vi 
K
K
 +  [( +  t ) K ] - e - e em
=t 
;
 x 

x j

x


x
j
j
K
j
 



 Dissipation



e
+ vj
t
qt = - C p  t 'vn'
Streamwise
= - C p
Wall-normal
Spanwise
K
eem
 2
BK
 0

C3 B02K

C3
C3
 2
BK
 0
"transition"
Ha/Re=1/225
4
"laminar"
Cf=2Ha/Re
2

e
 +  [( +  t ) e ] - C2 e e - e em
.
 x


x
K
j
e
j

 t T
Prt n
; Prt =  t /  t
MHD DEPENDENT TURBULENCE CLOSURES
Magnetic field
direction
8
Diffusion
Pr oduction
e
e  v
= C1  t  i
x j
K  x j
Cf x 1000
MHD K- e TURBULENCE MODEL
Experiment :
Re=29000
Re=50000
Re=90000
calculations
e
eem
 2
Be
 0

C4 B02e

C4
C4
 2
Be
 0
C3
C4
0.02
0.015
1.9exp{-1.0N} 1.9 exp{-2.0N}
1.9 exp{-1.0N}
1.9 exp{-2.0N}
0
0
1
2
3
4
5
(Ha/Re) x 1000
Comparison of UCLA model
to experimental data
1.5-D MHD K-e Flow Model
• unsteady flow
• height function surface tracking
• turbulence reduction near surface is
treated by specialized BCs
• effect of near-surface turbulence on
heat transfer modeled by variation of
the turbulent Prandtl number
Remarkable Progress on Small-Scale Experiments
with Science, Education, and Engineering Mission
Two flexible free surface flow test stands were planned, designed, and
constructed at UCLA with modest resources in less than a year
Purpose:
Our Experimental Approach
Investigation of critical issues
for liquid wall flow control
and heat transfer
1. Cost Effective
M-TOR Facility
- FLIHY dual use with JUPITER-II funds from Japan
For LM-MHD flows in
complex geometry and multicomponent magnetic field
2. Science-Based Education Mission
FLIHY Facility
3. Collaboration among institutions
For low-conductivity fluids
(e.g. molten salt) flow
simulation (including
penetrations) and surface heat
and mass transfer
measurement
- UCLA, PPPL, ORNL, SNL
- M-TOR built with recycled components, mostly by
students
- Several MS and Ph.D student theses
- Scientists from outside institutions
4. International Collaboration
- JUPITER-II (Tohoku Univ., Kyoto Univ., Osaka Univ.,
etc.)
- Several Japanese Professors/Universities participate
- IFMIF liquid target
Exploring Free Surface LM-MHD in
MTOR Experiment
•Study toroidal field and gradient effects:
Free surface flows are very sensitive to drag from
toroidal field 1/R gradient, and surface-normal fields
•3-component field effects on drag and
stability: Complex stability issues arise with field
gradients, 3-component magnetic fields, and applied
electric currents
•Effect of applied electric currents: Magnetic
Propulsion and other active electromagnetic restraint
and pumping ideas
•Geometric Effects: axisymmetry, expanding /
Ultrasonic Transducer Plots
contacting flow areas, inverted flows, penetrations
Timeof-flight
•NSTX Environment simulation: module
Microseconds
Without Liquid Metal
With Liquid Metal
95.1
91.5
87.9
84.2
80.6
77.0
73.4
69.8
66.2
62.6
59.0
55.4
51.8
48.1
44.5
40.9
37.3
33.7
30.1
26.5
22.9
19.3
15.7
8.4
4.8
12.0
1.2
MTOR Magnetic Torus and LM Flowloop:
Designed in collaboration between UCLA, PPPL and ORNL
-2.4
testing and design
FLIHY is a flexible facility that serves many
needs for Free-Surface Flows
Flow Control
Penetrations
(e.g. modified
back wall
topology)
• Large scale test
sections with
water/KOH
working liquid
• Tracer dye and
IR camera
techniques
3D Laser
Beams
KOH
Free Surface Interfacial
Transport
- Turbulence at free surface
- Novel Surface Renewal Schemes
• PIV and LDA
systems for
quantitative
turbulence
measurements
Fin
Thin
Plastic
KOH
Jacket
TwistedTape
JUPITER-II
US-Japan Collaboration on
Enhancing Heat Transfer
1.4 cm
45o Flow Direction
Surface Renewal
(e.g. Delta-Wing” tests)
Interfacial Transport Test
section length = 4 m
Dye Diagnostics for Interfacial
Mass Transport Measurements
Profile of dye penetration (red dots)
Local free surface (blue dots)
flow direction ~2 m/s
Dynamic Infrared
measurements of jet
surface temperature
Water jet
Impact of hot droplets on cold
water jet (~8 m/s) thermally
imaged in SNL/UCLA test
hot droplets
Hot droplet penetrating jet
Plasma-Liquid Surface Interactions
- Multi-faceted plasma-edge modeling validation with data from
experiments
- Experiments in plasma devices (CDX-U, DIII-D and PISCES)
Processes modeled for impurity shielding of core
Liquid lithium limiter in CDX-U
Validated Plasma Edge Models were extended to predict the
Physics Limits on LW Surface Temperature
Flowing LM Walls may Improve Plasma
Stability and Confinement
SNOWMASS
Several possible mechanisms identified at Snowmass…
Presence of conductor close to plasma boundary (Kotschenreuther) - Case
considered 4 cm lithium with a SOL 20% of minor radius
• Plasma Elongation  > 3 possible – with  > 20%
• Ballooning modes stabilized
• VDE growth rates reduced, stabilized with existing technology
• Size of plasma devices and power plants can be substantially reduced
High Poloidal Flow Velocity (Kotschenreuther)
• LM transit time < resistive wall time, about ½ s, poloidal flux does not penetrate
• Hollow current profiles possible with large bootstrap fraction (reduced recirculating
power) and EB shearing rates (transport barriers)
Hydrogen Gettering at Plasma Edge (Zakharov)
• Low edge density gives flatter temperature profiles, reduces anomalous energy
transport
• Flattened or hollow current density reduces ballooning modes and allowing high 
APEX Plasma-Liquid Interaction Tasks are Utilizing and Extending
State-Of-The-Art Codes with Comparisons to the Latest Data, and
Exploring Exciting Possibilities Identified in Snowmass
• Dynamic modeling of plasma equilibria uses the Tokamak Simulation
Code (TSC), a PPPL code validated with NSTX data. For example, TSC
simulations of NSTX equilibria were used to estimate the magnitude of
forces due to eddy currents on the liquid surface test module for NSTX
• Physicists are contributing exciting ideas for liquid walls
- Electromagnetically Restrained Blanket (Woolley)
- Soaker Hose (Kotschenreuther)
- Magnetic Propulsion (Zakharov)
• Studies of Innovative Wall Concepts are providing insight into nature
and control of plasma instabilities
- Stabilization schemes for resistive wall modes and neoclassical tearing
modes are of broad interest to the fusion community
- A new resistive MHD Code (WALLCODE) has been developed by IFS/UT
to explore the stabilizing properties of various conducting wall geometries
• Initial Results: Liquid metals can be used as conducting walls that
offer a means for stabilizing plasma MHD modes
Utilization of Liquid Metals for a Conducting Shell May
Allow Higher Power Density Tokamak Plasma
• Initial results from new WALLCODE resistive MHD code: Stable highly
elongated plasmas possible with appropriately shaped conducting shell
• Liquid metals may be used for the conducting shell
• Implications for fusion:
- High power density plasma (plus power extraction capability)
- Overcome physics-engineering conflicting requirements that reactor
designers have struggled with for decades
Results from WALLCODE: New IFS/UT resistive MHD code
n=0 Re sistive Wall Growth Rate vs. Elongation for
g x wall time
poloidal b = 0
rectangular vessel d/a = .1
10
9
8
7
6
5
4
3
2
1
0
d/a = .2
d/a = .1
1.5
2
2.5
3
elongation
3.5
4
4.5
* Instability growth rate depends on conformity of wall to plasma
Beta Limits for high elongation
(example of initial results)


2
.7
0
4.3%
3
.78
0
11.5%
4
.9
.1
14%
5
1.28
.5
22%
D
D
*
 indentation/minor radius
Progress toward Practical and Attractive
Liquid Walls: Many Creative Innovations
The APEX Approach to Problems
- Understand problems and underlying phenomena and science
- Search for Innovative Solutions: Our job is “to make things work”
- Modeling, analysis, and experiments to test and improve solutions
Examples of Creative Innovations
• New fluid candidates with low-vapor pressure at high temperatures (SnLi, Sn)
• “Surface Renewal”: New schemes to promote controlled surface mixing and wave
formation to reduce surface thermal boundary layer resistance
• Flow tailoring schemes to “control” flow around “penetrations”
• Two-stream flows to resolve conflicting requirements of “low surface temperature”
and “high exit bulk temperature”
• Toroidal Flow (“Soaker Hose”) concept to reduce MHD effects
• Novel schemes for electromagnetic flow control
• Creative design with over laid inlet streams to shield nozzles from line-of-sight
• Innovative design of “bag concept” with “flexible” SiC fabric structure
Clever creative design with overlaid streams
shields nozzles from line-of-sight to plasma
Outboard
Auxiliary
Stream
Inboard
Stream
Fast Flow Cassette
Assembly Cut at Mid-plane
STATE-OF-THE-ART 3-D TIME DEPENDENT FLOW 3-D CALCULATIONS
WAS KEY TO UNDERSTANDING PENETRATION PROBLEMS
3-D CFD Simulation Results
Potential Problems
• Fluid splash
• Fluid level rise
• Wake formation
3-D View of the Wake Following the Penetration.
2-D Velocity Magnitude in Planes
Perpendicular to the Flow Direction
Innovative Solutions Found and Confirmed by
FLOW-3D Calculations (experiments also planned)
III
II
I
IV
3-D Hydrodynamic simulation of penetration
accommodation when the back wall topology
surrounding the penetration is modified .
Modified back wall topology
surrounding the penetration.
I
III
II
IV
2-D Velocity magnitude in planes perpendicular to the flow direction
Finding innovative surface renewal
methods to improve heat transfer
• IDEA: Promote streamwise vortex
production by “delta-wing” backwall
structures
• Long-lived vortices should renew surface
and transport heat to the bulk flow.
• Technique borrowed from aerospace
applications
Flow Direction
Fin
Case Analyzed to Assess Effect
1.4 cm
45 o
Flow Direction
Liquid Layer Velocity
Liquid Layer Height
Fin Height
Fin Width
Spacing Between Fins
: 1.5 m/s
: 2.0 cm
: 1.4 cm
: 0.5 cm
: 0.5 cm
3D Thermofluid Simulations Confirm
Heat Transfer Enhancement
Free surface temperature distribution of
a Flibe flow over a plane wall, without
(left) and with (right) vortex promoters
without
2-D Temperature and
Velocity Distribution
downstream from vortex
promoters - vortex
generation and heat
transfer enhancement
clearly evident.
without
with
with
TWO-STREAM FLOW HAS THE POTENTIAL TO
ACHIEVE BOTH PLASMA COMPATIBILITY AND
HIGH THERMAL EFFICIENCY
X (U)
0

B
R


g r
Y (V)
The fast external stream removes
the surface heat flux, while the
slow internal stream serves as a
blanket:
• Plasma-facing liquid surface at low
temperature (to reduce vaporization; plasma
compatibility) while the thick liquid exits at
high bulk temperature for high efficiency
• Good heat transfer capabilities due to the high
velocity near-surface jet and KelvinHelmholtz instability between the two streams
• Reduced volumetric flow rate
• Lower erosion due to slower velocity in the
internal stream
CFD-MHD Calculations Show the Potential for
Practical Realization of the TWO-STREAM Idea
Low Conductivity Fluids: with a step-type initial velocity profile.
Liquid Metal: using “submerged walls”. Non-conducting or slightly
conducting walls submerged into the flowing liquid produce MHD
drag forming a “slow stream”, while liquid in the near-surface area is
accelerated due to the mass conservation.
thickness of the flow, m
0.80
Downstream development of the two-stream
flow produced with the submerged walls.
Sketch of the induced current
in the cross-sectional area.
Slow stream: U=7 m/s, h=40 cm.
Fast stream: U=10 m/s, h=10 cm.
The submerged walls are
slightly conducting: cw=210-6.
0.40
0.00
0
1
2
3
4
streamwise coordinate, m
5
6
7
Simulations of Flowing Lithium in NSTX using
Newly Developed MHD Free Surface Tools
“Center Stack +Inboard Divertor”, 2.5-D model
Thickness, m
0.012
1 - Hin=2 mm
2 - Hin=3 mm
3 - Hin=4 mm
0.008
0.004
3
2
1
0.000
0.0
0.4
0.8
1.2
1.6
2.0
Distance, m
“Inboard Divertor”, Flow3D-M
• Flow3D code was extended to
include MHD effects (Flow3D-M)
• New 2.5-D model and computer
code were developed to calculate
MHD free surface flows in a
multi-component magnetic field
Stable Li film flow can be
established over the center stack
NSTX: Heat flux can be removed with flowing
lithium along the center stack with acceptable
surface temperature (even with 4-mm film at 2m/s)
Results of Heat Transfer Calculations for NSTX Center
Stack Flowing Lithium Film
T about 340 C
(if Tin= 230 C)
3
2.5
2
1.5
1
0.5
Uo=2 m/s
4 m/s
SURFACE TEMPERATURE, K
ANSYS Model
surface heat flux
 Lithium surface
temperature
increases as flow
proceeds
downstream as a
function of
lithium inlet
velocity
120.00
Projected NSTX_center stack_heat
flux profile (total power = 10 MW)
6 m/s
80.00
8 m/s
10 m/s
40.00
0
-0.5
0.00
0
0.5
1
Height Above Midplane [m]
1.5
0.00
0.40
0.80
1.20
DISTANCE, M
1.60
2.00
 Two local
temperature
peaks are related
to local
maximums in the
heat flux profile
Liquid Wall Science is being Advanced in Several
MFE & IFE Research Programs
HYLIFE-II
NSTX Li module
3D Laser
Beams
KOH
Thin
Plastic
KOH
Jacket
TwistedTape
JUPITER-II
APEX CLiFF
IFMIF
Liquid Jet Research for IFE Chambers
High-velocity, oscillating
jets for liquid “pocket”
•flow trajectory and jet deformation
•primary breakup / droplet formation
•dissembly processes
•liquid debris interaction / clearance
•partial head recovery
High-velocity, low surfaceripple jets for liquid “grid”
•surface smoothness control
•pointing accuracy / vibration
•primary breakup / droplet ejection
Graphics from UCB
Oscillating IFE jet
experiments
and simulations
Flow
Direction
•Single jet water experiments
and numerical simulations
demonstrate control of jet
trajectory and liquid pocket
formation at near prototypic
Re
Experimental Data
from UCB
Flow
Direction
Regions flattened by
interaction with
neighboring jet
Simulations from
UCLA
Understanding mechanisms of flow
instability leads to improved control of
jet surface smoothness for IFE
• Upstream turbulence
and nozzle boundary
layer thickness
heavily influence
downstream jet
stability
• Turbulence
conditioning and
boundary layer
trimming in nozzle
dramatically improves
jet quality
Re = 75,000
L/D = 44
Re = 100,000
L/D = 44
w/ conditioning
w/o conditioning
UC Berkeley data
Modeling of Stationary
Jet Deformation
Modeling
UCLA
Experiment
•Initially rectangular jets deform
due to surface tension and
corner pressurization in nozzle
•Capillary waves from corner
regions fan across jet face - largest
source of surface roughness!
•Numerical simulations and
quantitative surface topology
measurements are critical
tools for understanding jet
deformation, and
controlling jet behavior
with nozzle shaping
LIF measurement of surface topology at Georgia Tech
Liquid Wall Science is important in many
scientific pursuits and applications
• Liquid Jet and Film Stability and Dynamics: fuel injection,
combustion processes, water jet cutting, ink jet printers, continuous
rod/sheet/ribbon/sphere casting, flood/jet soldering, ocean waves, hull design,
ocean/river hydraulic engineering, surfing, liquid walls for fusion reactors
• Liquid MHD / free surface interactions: melt/mold stirring
and heating, liquid jet/flow control and shaping, crystal growth, astrophysical
phenomena, liquid metal walls for particle accelerators and fusion reactors
• Liquid MHD / turbulence interactions: microstructure control
in casting, boundary layer control, astrophysical dynamos and plasmas, liquid
walls for particle accelerators and fusion reactors
• Free surface heat and mass transfer: oceanography,
meteorology, global climate change, wetted-wall absorbers/chemical reactor,
condensers, vertical tube evaporator, film cooling of turbine blades, impurity
control in casting, liquid walls for particle accelerators and fusion reactors
Watermark: Turbulent flow effect on dendrite formation in casting - Juric simulation
Temperature Rise (K)
What is Global Warming?
Increasing Green House Gases:
Humidity, CO2, Methane, NOx,
Sox etc.
Infra Red Absorption into
Green House Gases and
on the Earth surface
I.R. Absorption
Sun
Earth
I.R.
Radiatio
n
Preserving Heat in the Air
Air
Temperature Rise in the Air
I.R.:Infra Red
Year
Free surface mass transport is
affecting CO2 concentrations
Missing Sink Problem over past 30 years
Measured atmospheric CO2 increase (34 ppm)
- Spent Fossile Fuel emissions (61 ppm)
= Missing Sink(-27 ppm)
?
Turbulent Heat and Mass transfer across Free Surface ?
Wind flow
Free surface contour wind-driven calculation
CO2 absorption at the turbulent
free-surface deformed by the
shear wind, by means of direct
numerical solution procedure for
a coupled gas-liquid flow
Coherent Structures in Wind-driven
Turbulent Free Surface Flow
Wind
Simulation by
T. Kunugi et al.
Water
Atmospheric Pressure Contour Surface (Green)
Gass Exchange Rate, kL (m/s)
10-3
W ind tunnel experiment
-4
10
10-5
10-6
High Speed Gas Side Regions (Brown)
High Speed Water-Side Regions (Blue)
Streamwise Instantaneous Velocity (Color Section)
: Liss & Merlivant (1986)
X : Measurements at sea
: Present study
10-7
DNS
-1
10
100
Friction Velocity, u τ(m/s)
Some Common Aspects between Global Warming
and Fusion Science Thermofluid Research
Similar Phenomena
•High Pr flow with radiation heating at free surface from plasma
•High Sc flow with CO2 absorption at free surface of sea
Similar Flow Characteristics
•Re is high, both have the similar turbulence characteristics.
•MHD (fusion) and Coriollis (global warming) forces can influence
the average velocity
Heat and Mass Transfer Similarity
•High Pr, very low thermal diffusivity->very thin thermal boundary
layer->large temperature gradient at interface
•High Sc, very low molecular diffusivity->very thin concentration
boundary layer->large concentration gradient at interface
.
Liquid Jet Stability and Breakup
Inkjet Printer quality is
hampered by formation
of “satellite” droplets
Simulation of commercial inkjet
by Rider, Kothe, et al. - LANL
Micro-injector increases relative importance
of surface tension by decreasing size eliminates satellite droplets and improves
precision
Data from Ho - UCLA
Vertical B field effects on
Liquid Metal Film Flows
Continuous sheet casting
can produce smooth free
surfaces and film thickness
control via MHD forces
Film thickness profiles for
various Hartmann Numbers
Simulation by Lofgren, et al.
Reflections on 19th & 20th Centuries
1850:
Navier-Stokes Equation
1873:
Maxwell’s Equations
1895:
Reynolds Averaging
1900-1960’s:
-Averaging techniques, Semi-empirical approach. Heavy reliance on Prototype
Testing (e.g. wind tunnels for aerodynamics).
1960’s - 1970’s:
-Supercomputers allow direct solution of N-S for simple problems. Advances in
Computational Fluid Dynamics (CFD), e.g. utilization of LES technique.
1980’s - 1990’s:
-Rapid advances to Teraflop Computers
-Rapid advances in CFD and in experimental techniques
-Turbulence structure “simulated” and “observed” for key problems
-Better understanding of fluid physics and advanced “Prediction” tools
-Paradigm Shift:
- From “mostly experimental for empirical global parameters” to “larger share
for CFD: simulation first followed by smaller number of carefully planned
experiments aimed at understanding specific physics issues and verifying
simulation.”
21st Century Frontiers
Moving Beyond “Prediction” of Fluid Physics
To “Control” of Fluid Dynamics
• With the rapid advances in teraflop computers, fluid dynamicists are increasingly able to
move beyond predicting the effects of fluid behavior to actually controlling them; with
enormous benefits to mankind!
Examples
• Reduction in the Drag of Aircraft
The surface of a wing would be moved slightly in response to fluctuations in the
turbulence of the fluid flowing over it. The wings surface would have millions of
embedded sensors and actuators that respond to fluctuations in the fluids, P, V as to
control eddies and turbulence drag. DNS shows scientific feasibility and MEMS can
fabricate integrated circuits with the necessary microsensors, control logic and actuators
• Fusion Liquid Walls
Control of “free surface-turbulence-MHD” interactions to achieve fast interfacial
transport and “guided motion” in complex geometries (“smart-liquids”)
• Nano Fluidics: Pathway to Bio-Technologies
Appropriately controlled fluid molecules moving through nano/micro passages can
efficiently manipulate the evolution of the embedded macro DNA molecules or affect the
physiology of cells through gene expression.