Multiphase starting jets and plumes are widely observed in nature and engineering systems. An environmental engineering example is open-water disposal of sediments. The present study numerically simulates such starting jets/plumes using Large Eddy Simulations. The numerical scheme is first validated for single phase plumes, and the relationship between buoyancy and penetration rate is revealed. Then, the trailing stem behind the main cloud is identified, and the the formation number (critical ratio U[delta]t/D, where U, D and [delta]t are discharge velocity, diameter and duration) that determines its presence is determined as a function of plume buoyancy. A unified relationship for starting plumes is developed to describe behaviors from negative to positive buoyancy. In multiphase simulations, two-phase phenomena are clarified including phase separation and the effect of particle release conditions. The most popular similarity law to scale up from the lab to the field (Cloud number scaling) is validated by a series of simulations. Finally, an example of sediment disposal in the field is given based on the present study. In related theoretical analysis, an analytical model on the vortex ring is developed and found to agree well with the direct numerical simulation results.
Formation of low mass protostars and their circumstellar disks
Numerical and analytical studies of single and multiphase starting jets and plumes
1. Numerical and Analytical Studies of Single
and
Multiphase Starting Jets and Plumes
Ruo-Qian (Roger) Wang
Dept. of Civil and Environ. Eng., MIT
Thesis Committee: Dr. Heidi Nepf
Dr. Ole Madson
Dr. Adrian Wing-Keung Law
Dr. Roman Stocker
PhD advisor: Dr. Eric Adams
2. Jets and Plumes
2
Oil spill plume
Jack Cook, WHOI
Sneezing (http://blogs.discovermagazine.com)
Spores spreading (http://blogs.discovermagazine.com)
3. What’s dredging and sediment disposal?
3A dredge working on Lake Michigan. (EPA)
4. Where do we need dredging?
I. Land reclamation
4
stefaniestoelen.blogspot.com
6. Where do we need dredging?
II. Navigation
6
http://www.travelskyline.net/view-crystal_symphony_panama_canal-1024x768.html
7. Where do we need dredging?
III. Environmental Restoration
7
Lindsey B., Grade 8, North Carolina. One of the 2012-2013 winners in the Keep the Sea Free of Debris art contest
9. Where do we need dredging?
IV. Flood Prevention and Beach Nourishment
9
http://www.theguardian.com/environment/2014/jan/29/flooding-england-private-funding-scheme
11. Applications of Dredging
I. Land reclamation
II. Navigation
III. Environmental restoration
IV. Flood prevention and beach nourishment
V. Mining
VI. Fishing
VII.Construction (e.g. ports, bridges, and other infrastructures)
11
12. Outline
• Research objectives
• Numerical method – a multi-scale challenge
• Physics of settling particle clouds
– Main cloud
– Trailing stem
• Theoretical model of vortex rings
• Summary and a case study
12
13. Research Objectives
• Accurate placement
• Turbidity reduction
• Dissolved contaminants tracking
• Operation guidance
• Save cost
• Reduce environmental impact
13
14. State of knowledge in particle clouds
Koh and Chang (1973)
Ad hoc loss mechanism: Abdelrhman and
Dettmann (1993) and Johnson and Fong
(1995) STFATE
Gravity
Particle Cloud
Drag + Added Mass
Entrainment
Phase separation in the main cloud
Trailing stem
15. Numerical models can help our understanding
“CFDEM”
CFD-DEM coupling
OpenFOAM
Large Eddy Simulations
LIGGGHTS
ParticleTracking
One-way Two-way Four-way Four-way+
Passive Particles Particle-fluid
interaction
Particle-fluid
Interaction
+
Particle-collision
Particle-fluid
Interaction
+
Particle-collision
+
Coalesce and break up
15
16. Governing Equations
F
up
dt
d
mp
WHALDSG FFFFFFFF
// Lagrangian Track
// Neglect History and
Wall interaction terms
Fluid
Solid
// Fractioned N-S equation
¶a f
¶t
+ Ñ× a f uf( )= 0,
¶ a f uf( )
¶t
+ Ñ× a f uf uf( )= -a f Ñ
p
rf
- Rsl + Ñ×t,
My Contributions
16
19. A proposed scale-separation solution
Characteristic cell volume @ center ~=1.5 particle volume
2nd order discretization in space
4th order discretization in spacek
E
2π/ηEnergy
Input
Particle
Size
Grid cell
19
20. Comparison to experiments validates
the present numerical scheme
Numerical Simulation Lab Experiment
20
21. A series of numerical simulations was performed
15 Cases
– Particle diameter dp=0.26-0.73 mm
– Total mass Mtotal=2-3 g
– Release radius R0=3.9-9 mm
– Aspect ratio A=H/R0=1.2-15
21
H
2R0
22. Definition of the phase separation
22
Phase separation
in the main cloud
Trailing stem
23. Phase Separation
Separation time by Separation height and time
0 200 400 600 800 1000 1200
0
200
400
600
800
1000
1200
Ra
T
sp
/(T
s
A1/4
)
Tsp
R0
2
/ B / r0( )1/2 = 0.85A1/4
Ra Hsp
R0
= 2.4
Tsp
R0 / ws
Ra =
B
r0ws
2
R0
2
23(Wang et al., submitted to IJMF)
25. Settlement of Clouds
zs
B / r0( )1/2
/ ws
=
2A0.17 t
B / r0( )1/2
/ ws
2
æ
è
ç
ö
ø
÷
0.66
t < Tsp( )
Hsp +1.1
t -Tsp
B / r0( )1/2
/ ws
2
t > Tsp( )
ì
í
ï
ïï
î
ï
ï
ï
zf
B / r0( )1/2
/ ws
=
1.5A0.3 t
B / r0( )1/2
/ ws
2
æ
è
ç
ö
ø
÷
3/5
t < Tsp( )
Hsp + 0.75
t -Tsp
B / r0( )1/2
/ ws
2
æ
è
ç
ö
ø
÷
0.8
t > Tsp( )
ì
í
ï
ï
ï
î
ï
ï
ï
Solid Phase Fluid Phase
25
26. Growth of Clouds
rs
B / r0( )1/2
/ ws
=
rf
B / r0( )1/2
/ ws
= 0.7
t
B / r0( )1/2
/ ws
2
æ
è
ç
ö
ø
÷
0.3
Solid Phase Fluid Phase
26(Wang et al., submitted to IJMF)
27. What happen if the particles are not the same in size?
Cases Distr. dp (mm) d50 (mm) w50 (cm/s) wmax (cm/s)
Bu1 Top-hat 0.26-0.73 0.61 8.8 10.6
Bu2 Top-hat 0.26-0.76 0.64 9.3 11.2
Bu3 Top-hat 0.43-0.60 0.53 7.6 8.7
Bg1 Gaussian 0.46-0.57 0.52 7.4 8.3
Bg2 Gaussian 0.22-0.81 0.57 8.2 12.0
27
28. Thermal
Poly-dispersion inThermal and Dispersive stages
Thermal phase – d50
Dispersive phase – dmax
Bu1 Bu2 Bu3 Bg1 Bg2
Before
Phase
Separation
After
Phase
Separatio
n
28
(Wang et al., submitted to IJMF)
29. How to extrapolate experimental results
from lab to field scale?
29
Lab Field
http://automaticburger.blogspot.com/http://www.disboards.com/showthread.php?p=42145760
30. Similarity Law from Small- to Full-scale
• Solid phase front
Ra =
B
r0ws
2
R0
2
=
Buoyancy
Drag
Case R (cm) M (g) Aspect ws(cm/s) dp (mm) Np Ra
B 0.9 3 1.19 7.3 0.51 17k 41
BL4 3.6 192 1.19 14.6 1.008 143k 41
BL16 14.4 12,288 1.19 29.2 2.336 736k 41
Wang et al. (submitted to JHE)
30
31. Suggestion to Improve Field Operations
yosemite.epa.govwww.southchinashipyard.com
31
Tsp = 0.85
B / r0( )1/2
ws
2
A1/4
40. A steady state solution?
ExperimentNumerical Simulation
44
41. At steady state, in high Reynolds
number but laminar flow
22
2
2
2
1
rrrrx
u
x
v
rt
r
rrxr
1
2
2
2
2
y = Cl1M
-
l2
4a
,
1
2
(ar2
)+ Cl2W
-
l2
4a
,
1
2
(ar2
)
é
ë
ê
ê
ù
û
ú
ú-¥
¥
ò [cos(lx)- isin(lx)]dl.
45
42. The present model matches the numerical simulations better
Simulations Linear Model Low Reynolds number The Present
46(Wang et al., submitted to AMM)
43. Summary
• A numerical method for multiphase Large-Eddy
Simulations is developed
• Physics of two-phase settling particle clouds is analyzed
– Initial aspect ratio, phase separation, penetration and growth
• Trailing stem presence of starting plumes is determined
• A theoretical solution to vortex ring is derived
47
44. A Case Study
48
H=30 m
Average particle diameter dp=0.5 mm
Particle density ρp=2.5 g/cm^3
Settling velocity ws=7.1 cm/s
Settling time Tsp=2.9 min
Total Buoyancy B=1086 N
Volume V=0.089 m^3
Check A=1<6.5 and Ra=337 <1000
If relaxed to Ra=1000,
The maximum volume to release
Vmax=0.26 m^3
45. Acknowledgment
• PhD Advisors:
– Dr. Eric Adams (MIT)
– Dr. Adrian Wing-Keung Law (NTU, Singapore)
• Thesis Committee: Dr. Heidi Nepf, Dr. Ole Madson, Dr. Roman Stocker
• Group Members:
– Dr. Adrian Chun-Hin Lai (SMART, Singapore)
– Dr. Bing Zhao (NTU, Singapore)
– Dr. Dongdong Shao (Beijing Normal Univ, China)
– Dr. Dai Qin (Shanghai University, China)
– Dr. Zhenhua Huang (Univ of Hawaii)
– Mr. James Gensheimer III (US Navy)
– Mr. Godine Chan (MIT)
– Mr. Jenn Wei Er (NTU, Singapore)
– Ms. Cindy Wang (MIT)
• Collaborators:
– Dr. Oliver Fringer (Stanford Univ)
– Dr. Yujun Wang (MIT)
– Dr. Alex Sappok (MIT)
– Dr. Guoxing Huang (Dalian University of Technology, China)
• My family and my colleagues from EFM Group, Parsons, CENSAM, and MIT
49
Editor's Notes
Thank you for your introduction. Hi everyone! Thank you for being here. Today, I am very happy to share my research on the physics of sediment disposal in ports and harbors.
Use Your mouth, raise your voice more often!!! Think about what’s next!
First of all, what’s dredging? Dredging operations include two components. First, it means excavation from the bottom of the water. And second, it means disposal of the dredged materials. The picture shows a dredger barge excavating sediments in the Lake Michigan.
Dredging is applied in various fields. The first application is in land reclamation. I believe many of you have seen this picture before. Do you know where it is? Yes, this is the Palm island in Dubai. Dredging can be used to build such beautiful artificial island.
Let’s see another example from Singapore. This is the coastal line of Singapore in 1950 and this is 2002. You can see all the red areas are created by land reclamation, including the new airport and all the industrial islands. Singapore still has an ambitious plan to expand its land area, but they have no sand resources. So they have to import from its neighbors like Malaysia and Indonesia. Recently, these two countries stop selling sands to Singapore, because a small island disappeared in Indonesia due to sand smuggling. As a result, Singapore has to purchase sediment from farther countries like Vietnam or Cambodia, which dramatically increased the cost of sediment, from $ 0.8/m^3 to $8.5 per cubic meter. Therefore, they need to conserve the use of sediment in their future projects.
Another important application of dredging is in Navigation. This is the Panama canal. This canal is not only important in global trade, it also sets the standard of the ship manufacturing industry. The size of the canal limit the size of the ship that can go through. Now, the canal is under expansion and larger boats can be manufactured. It means the US also need larger and deeper ports to accommodate the enlarged ships. These projects require a lot of dredging.
If your ship is too big and cannot pass through this canal, then it is useless to transportation from the New York to the LA. Now this canal is under expansion, which itself requires a lot of dredging. In addition, ports in the US need have to be bigger and deeper for the future trading demand.
Dredging is also an important tool for environmental remediation. I really like this picture. Look at those cute shellfish busy cleaning the bottom of the harbor! Why is that? Because the sediment is dirty! By estimation, the US dredges around 200 million m3 of sediments every year. And 10 to 20% are contaminated by PCB, DDT, or heavy metals. Therefore, people need a special treatment to those dredged materials.
This issue is especially significant in the Boston Harbor Navigation Improvement Project. The sediment in Boston Harbor is heavily contaminated by toxic materials due to a poor waste water treatment plan in the past. The toxic dredged materials were disposed using a technique called Aquatic Cell Disposal. The basic produces are shown here. …… This technique is encouraged by the Corps of Engineers and promoted by EPA.
Navigation Improvement project. Because this city used to have a poor waste water treatment plan, now the dredged materials are toxic. To solve this problem, the project used a technique called confined aquatic cell disposal, which is encouraged by corps of engineers and promoted by EPA.
Dredging is important for flood prevention. A poorly dredged river can cause the rise of river bed and therefore flooding. The people live near this river in England are obviously not happy. They need dredgers!
Long island also needs dredging for flood prevention and beach nourishment. This is the beach in Montauk after the Hurricane Sandy. The similar challenges can be seen in many places here. The corps of engineers is considering a series of coastal line protection projects as shown here. Therefore, dredging will be a local civil engineering topic for years.
In the following talk, I will first introduce our research objectives and the numerical method. Then, I will talk about our numerical results and the physics of settling particle clouds, including the main cloud and the trailing stem. Next, I will introduce a theoretical model that we have derived. At last, I will summarize my talk and outline my future research plan.
----- Meeting Notes (3/6/14 15:17) -----
remove "the", put Koh and Chan 1973
Traditionally, people used Koh and Chang’s model to describe the particle cloud. They treat the cloud as a mixture of particles and fluid and take account of the drag and added mass force, and the entrainment to allow its growth. Later on, researchers added ad hoc loss mechanism to allow the particles and fluid to separate. However, we found some significant discrepancies between their model and our lab observation. The right-hand side is a photo image from our lab. We released the particles together with rodamin dye. So the blue area in the photo are the particles and the red area is the tracer dye, which represents the dissolved contaminants released with the sediment disposal. From this picture, we can see the Koh and Chang’s model misses two important characteristics: first, the phase separation between the particle and the fluid phase is not captured. Second, the trailing stem behind the main cloud is not included in their model. Therefore, we try to use our own study to improve the model.
----- Meeting Notes (3/6/14 16:17) -----
break up
Explain colorbar, pausein middle explain
No details of numbers
----- Meeting Notes (3/6/14 16:17) -----
small S
Rayleigh number is important variable, A is new. Original form
A is new
Two-phases are new, fonts
Solid and fluid, remove mono-disp, figures first, collaps
----- Meeting Notes (3/6/14 16:17) -----
Physics of two-phase
Trailing stem prevents the presence of trailing ste,
----- Meeting Notes (3/6/14 16:17) -----
move to the middle
My research is about dredging and disposal of sediments. Where do we need dredging? First, it can be used in land reclamation. Artificial islands can be built by disposal of sediments. One example is the beautiful palm islands in middle east. Second, dredging is an important tool for navigation. Especially after the expansion of Panama canal, bigger ships will visit the US. We need to deepen the ports and harbors to accommodate them. In addition, dredging can be used to improve the drainage channel to control the flood and help protect the coastal line against the hurricanes. This will become more important with climate change. At last, dredging can also be used in environmental remediation. Dirty sediments can be removed and relocated to restore the environment.
Let’s start the story from the big picture. World widely, the dredging market is rising quickly especially before 2009. After the financial crisis, the market is recovered and booming again. Now the total market has hit almost 12 billion euros. This market can be divided into different areas.
As shown in the map, 6 areas are considered to have the best potential market, including Brazil, Africa, Europe, middle east, Asia and Australia. Among them, the biggest market is in south east Asia.
Let’s come back to the US. The US has the second largest market, just after China. Similarly, the market is experiencing a strong growth before 2009. After a downturn, the market is revering quickly, especially with the big need after the hurricane sandy. In a recent survey, the dredging projects can be classified into 4 categories. The maintenance of the existing ports takes the biggest. The capital dredging, which means deepening the port for bigger trade by ship transportation and land reclamation, takes the second largest. The coastal protection is closely following and there are increasing needs. The last part is by River and lakes, which majorly concerns on the environmental restoration. By estimation, annually, the US dredges 200 m3 sediment and 10 to 20% are contaminated, which needs a special management.
I am also enthusiastic on other environmental flows, e.g. the oil spill in the gulf. The spill plumes driven by natural gas bubbles and oil droplets rises and entrains a strong water current. The plume has a complex structure. With an extension to my current numerical model, I can perform a series of numerical simulations on it. Back in MIT and in Texas, I have colleagues working on the experimental part of this project. Their experimental results could be used to compare with and validate my numerical model.
Another interesting topic I’d like to explore is Biofilm. Biofilm is present everywhere in water and you can even find them in your mouth. Recent study shows that, the biofilms formed at the sediment surface can fundamentally change sediment transport, but the underlying mechanisms is not well studied. I am interested in how we can use numerical simulations to reproduce the observations and explore the underlying physics.
