The document describes a CFD modeling study of Lake Binaba in Ghana. It provides background on CFD modeling and its applications. It then describes Lake Binaba, including its location, dimensions, and the aims of the study, which are to simulate circulation patterns, temperature distribution, and evaporation. The document outlines the CFD modeling process, including developing the computational mesh from bathymetry data, applying boundary conditions based on meteorological measurements, and using OpenFOAM to solve the governing equations.

1. Introuduction Lake Binaba Lake Modeling Conclusion
CFD Modeling of Shallow and Small
Lakes
(Case Study: Lake Binaba)
Ali Abbasi
Nick van de Giesen
Department of Water Management
Delft University of Technology
November 28, 2013
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2. Introuduction Lake Binaba Lake Modeling Conclusion
1
Introuduction
What is CFD?
Why CFD?
Where is CFD Used?
Numerical Methods
Modeling
Flow Conditions
2 Lake Binaba
Description
Aims of the study
3
Lake Modeling
CFD Model
Pre-processing
Solving the Flow Field
Post-processing
4 Conclusion
Conclusion
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3. Introuduction Lake Binaba Lake Modeling Conclusion
1
Introuduction
What is CFD?
Why CFD?
Where is CFD Used?
Numerical Methods
Modeling
Flow Conditions
2 Lake Binaba
Description
Aims of the study
3
Lake Modeling
CFD Model
Pre-processing
Solving the Flow Field
Post-processing
4 Conclusion
Conclusion
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4. Introuduction Lake Binaba Lake Modeling Conclusion
What is CFD?
CFD : Computational Fluid Dynamics
The result of the confluence of fluid dynamics and a range
of allied subjects:
Numerical Methods
Grid Generation
Computational Geometry
Computer-aided Geometric Design
Computer Graphics
Parallel Computing
Simulation of fluid engineering systems using modeling and
numerical methods
Analytical Fluid Dynamics(AFD) and Experimental Fluid
Dynamics(EFD)
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5. Introuduction Lake Binaba Lake Modeling Conclusion
Why CFD?
Analysis and design:
more cost effective and more rapid than EFD
CFD provides high-fidelity database for diagnosting flow
field
Simulation of physical fluid phenomena that are difficult
for experiments:
full scale simulations
environmental effects(wind, weather, etc.)
hazards (explosions, pollution)
physics (plantetary boundary layer)
Knowledge and exploration of flow physics.
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6. Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Aerospace
Automotive
Biomedical
Hydraulics
Marine
Oil & Gas
Power generation
...
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7. Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 1 : Smoothing the cap over a swimmer´ head significantly improves
s
hydrodynamic performance
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8. Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 2 : Fishway optimization: a numerical modeling study
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9. Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 3 : CFD: a valuable design tool in water resources
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10. Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 4 : CFD modeling of water flow in a basin
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11. Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 5 : Trees will reduce campus storms(Dr. Sasa Kenjere-Delta Magazine)
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12. Introuduction Lake Binaba Lake Modeling Conclusion
Numerical Methods
The continuous Initial Boundary Value Problems(IBVPs)
are discretized into algebraic equations using numerical
methods
numerical methods include:
Discretization method
Solvers and numerical parameters
Grid generation and transformation
High performance computation(HPC) and post-processing
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13. Introuduction Lake Binaba Lake Modeling Conclusion
Modeling
Modeling is the mathematical physics problem formulation
in terms of continuous initial boundary value
problem(IBVPs)
IBVP is in the form of Partial Differential
Equations(PDEs) with appropriate boundary conditions
and initial conditions.
Modeling includes:
Geometry and domain(simple and complex geometry, size
and shape)
Coordinates
Governing equations
Flow conditions
Initial and boundary conditions
select on of models for different applications
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14. Introuduction Lake Binaba Lake Modeling Conclusion
Flow Conditions
Based on the physics of the fluids phenomena, CFD can be
distinguished into different categories using different criteria:
Viscous vs. Inviscid (Re)
External flow or Internal flow(wall bounded or not)
Turbelent vs. Laminar(Re)
Incompressible vs. Compressible (Ma)
Single- vs. Multi-phase flow
Thermal/density effects(Pr)
etc.
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15. Introuduction Lake Binaba Lake Modeling Conclusion
1
Introuduction
What is CFD?
Why CFD?
Where is CFD Used?
Numerical Methods
Modeling
Flow Conditions
2 Lake Binaba
Description
Aims of the study
3
Lake Modeling
CFD Model
Pre-processing
Solving the Flow Field
Post-processing
4 Conclusion
Conclusion
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16. Introuduction Lake Binaba Lake Modeling Conclusion
Description
Lake Binaba:
Location: an artificial lake located in northern Ghana
Surface: the average area of the lake surface is 4.5 km 2
Average depth: only 3 m
Maximum depth: 7 m
Usage: a small reservoir, used as a form of infrastructure
for the provision of water
Air temperature: fluctuates between 24 C and 35 C
Water surface temperature: varies from 28 C to 33 C
Climate: (semi-)arid region
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17. Introuduction Lake Binaba Lake Modeling Conclusion
Description
Location
Lake Binaba
Figure 6 : Lake Binaba in Ghana
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18. Introuduction Lake Binaba Lake Modeling Conclusion
Description
Location
Lake Binaba
Figure 7 : Location of lake Binaba(Google earth)
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19. Introuduction Lake Binaba Lake Modeling Conclusion
Aims of the study
To develop a three-dimensional time-dependent
hydrodynamic and heat transfer model(CFD model)
Simulating the effects of wind and atmosphere conditions
over a complex bathymetry
To predict the circulation patterns as well as the
temperature distribution in the water body
To compute total heat storage of small shalow lakes and
reservoirs in order to estimate evaporation from water
surface
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20. Introuduction Lake Binaba Lake Modeling Conclusion
1
Introuduction
What is CFD?
Why CFD?
Where is CFD Used?
Numerical Methods
Modeling
Flow Conditions
2 Lake Binaba
Description
Aims of the study
3
Lake Modeling
CFD Model
Pre-processing
Solving the Flow Field
Post-processing
4 Conclusion
Conclusion
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21. Introuduction Lake Binaba Lake Modeling Conclusion
CFD Model
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Figure 8 : CFD simulation workflow
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22. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Main steps in preparing the bathymetry of lake to use in CFD
modeling:
Reading initial point cloud (x,y,z coordinates from text file)
Adding extra points in point cloud to improve the
generated STL file
Generating the STL file
Cleaning & reapairing the STL file
Generating the computational mesh or CFD mesh
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23. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Reading initial point cloud
Reading the coordinates of points from a text file(points.asc):
Figure 9 : Initial point cloud: 642 points (x,y,z)
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24. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Adding extra points in point cloud to improve the generated STL file
Adding extra points to define the water surface
Adding extra points to improve the bathymetry
Using ArcMap to interpolate between points
Figure 10 : Improved point cloud: 68802 points (x,y,z)(V.S:100)
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25. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Generating the STL file
STL (STereoLithography) format is similar to a TIN,
except it defines the shell of a volume with a set of
interlocking triangular facests:
facet normal ni nj
outer loop
vertex v1x
vertex v2x
vertex v3x
endloop
endfacet
nk
v1y v1z
v2y v2z
v3y v3z
UsingMeshLab(free and open-source STL generator)
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26. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Generating the STL file
Figure 11 : STL file from meshLab(V.S:100)
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27. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Cleaning the STL file
The generated STL file should be clean to can be used in
CFD modeling
Using addmesh (free and open-source STL cleaner)
Figure 12 : Final STL file(V.S:100)
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28. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Seperating Boundaries
Water surface
Bottom and sides of lake
Figure 13 : Final geometry used in meshing(V.S:100)
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29. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Generating the computational mesh or CFD mesh
Refinig the mesh near the boundaries
nPoints:9,241,729; nCells:7,913,145
∆x = 1.5m; ∆y = 1.6m; ∆z = 0.25(0.125)m
Figure 14 : CFD mesh(Vertical Scale:100)
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30. Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Checking the mesh
Generated mesh should be satisfy the criteria
Figure 15 : z component of normal vector of cells(V.S:100)
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31. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Equations
Continuity equation:
∂uj
= 0,
∂xj
(1)
Momentum equations using Boussinesq approach
∂ui
∂
+
(uj ui )
∂t
∂xj
−
∂
∂xj
−
νeff
∂ui ∂uj
+
∂xj ∂xi
−
2
3
∂uk
∂xk
δij
=
(2)
∂p
+ gi [1 − β(T − Tref )]
∂xi
Temperature in the water body
∂T
∂
∂ ∂T
+
(Tuj ) − κeff
(
) = ST
∂t
∂xj
∂xk ∂xk
(3)
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32. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Initail Conditions
ICs should not affect final results
Only affect the number of iterations to reach converged
solution
Figure 16 : Initial condition for T
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33. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Boundary Conditions
Temperature
ρ0 Cp κeff
∂T
∂z
= Hnet
(4)
τsurf ,u = ρ0 (νt + ν)
∂u
∂z
(5)
τsurf ,v = ρ0 (νt + ν)
∂v
∂z
(6)
surf
Velocity
2
2
τsurf ,u = CD ρair v10 + u10
2
2
τsurf ,v = CD ρair v10 + u10
1
2
1
2
.u10
(7)
.v10
(8)
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34. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Meteorogical measurements
40
Tair
T [C]
35
Twater−surf ace
30
25
20
15
0
10
20
30
40
50
1000
HLA
HeatFluxes[W/m2 ]
800
HLW
600
Hns
400
HS
HE
200
Hnet
0
Rs
−200
−400
0
10
20
30
40
Time[hr]
Figure 17 : Time-dependent parameters using as B.C
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35. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Meteorogical measurements
Figure 18 : Time-dependent parameters using as B.C
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36. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Solver
Open Source Field Operation and Manipulation
(OpenFOAM)
Open-Source Library
Free of Charge
in LINUX
C++ Library
Linking with PYTHON
Special Issue
new SOLVERS and UTILITIES Can be Created by
USERS
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37. Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow Field
Running in parallel
OF runs in parallel
We need to run the model in parallel
Decomposing the domain accoeding to the availabe sources
Using MPI
OF was tested at least for 1000 cores!
Using GPU
Lake Binaba
We are running the model on 64 and 36 nodes
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38. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Figure 19 : Bathymetry of lake Binaba
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39. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Velocity
Figure 20 : Velocity in t=3930 s (V.S:10)
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40. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Velocity
Figure 21 : Velocity in t=3930 s (V.S:10)
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41. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Temperature
Figure 22 : Temperature in t=3930 s (V.S:10)
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42. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Source term in T
Figure 23 : Temperature source term in t=3930 s (V.S:10)
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43. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Velocity
Figure 24 : Velocity in t=5640 s (V.S:10)
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44. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Temperature
Figure 25 : Temperature in t=5640 s (V.S:10)
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45. Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Velocity
Figure 26 : Velocity in t=7440 s (V.S:10)
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46. Introuduction Lake Binaba Lake Modeling Conclusion
1
Introuduction
What is CFD?
Why CFD?
Where is CFD Used?
Numerical Methods
Modeling
Flow Conditions
2 Lake Binaba
Description
Aims of the study
3
Lake Modeling
CFD Model
Pre-processing
Solving the Flow Field
Post-processing
4 Conclusion
Conclusion
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47. Introuduction Lake Binaba Lake Modeling Conclusion
Conclusion
CFD modeling and graphical output provides a detailed
visual representation of the modeled system
Model results provides a high degree of confidence for
project owners, designers, and other stakeholders
Computational fluid dynamics (CFD) analysis has proven
to be a valuable design tool in the water resources
Modelling is one of the best means to gain understanding
of complex flow fields
Wind over water surface affects lake currents, sensible and
latent heat fluxes
Buoyancy effect due to density gradiant in water body
should be considerd in temperature profile
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48. Introuduction Lake Binaba Lake Modeling Conclusion
Thanks For your Attention
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