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IntrouductionLake BinabaCFD ModelConclusion
CFD Modeling of Shallow and Small Lakes
Ali AbbasiNick van de Giesen
Delft University of TechnologyWater Resources Management
February 13, 2014
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IntrouductionLake BinabaCFD ModelConclusion
Aims of the study
Outline
1 IntrouductionAims of the study
2 Lake BinabaDescriptionWhy 3D-CFD Model?
3 CFD ModelCFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
4 ConclusionConclusion
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IntrouductionLake BinabaCFD ModelConclusion
Aims of the study
Aims of the study
The following goals are considered:
To develop a three-dimensional time-dependent hydrodynamicand heat transfer model(CFD model)
Simulating the effects of wind and atmosphere conditions over acomplex bathymetry.
To predict the circulation patterns as well as the temperaturedistribution in the water body.
To estimate total heat storage of small and shallowlakes(reservoirs) in order to estimate evaporation from watersurface.
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IntrouductionLake BinabaCFD ModelConclusion
DescriptionWhy 3D-CFD Model?
Outline
1 IntrouductionAims of the study
2 Lake BinabaDescriptionWhy 3D-CFD Model?
3 CFD ModelCFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
4 ConclusionConclusion
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IntrouductionLake BinabaCFD ModelConclusion
DescriptionWhy 3D-CFD Model?
Description
Lake Binaba:
Location: an artificial lake located in northern Ghana
Surface: the average area of the lake surface is 4.5 km2
Average depth: only 3 m
Maximum depth: 7 m
Usage: a small reservoir, used as a form of infrastructure for theprovision 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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IntrouductionLake BinabaCFD ModelConclusion
DescriptionWhy 3D-CFD Model?
Location
Lake Binaba:
Figure: Location of lake Binaba
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IntrouductionLake BinabaCFD ModelConclusion
DescriptionWhy 3D-CFD Model?
Location
Lake Binaba:
Figure: Location of lake Binaba(Google earth)
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IntrouductionLake BinabaCFD ModelConclusion
DescriptionWhy 3D-CFD Model?
Why 3D-CFD Model?
Using 3D-CFD Model for shallow lakes:
Inalnd water bodies such as lakes and reservoirs are veryimportant parts of the continental land surface.
Understanding the heat storage in lakes and reservoirs is essentialto estimate evaporation in energy budget methods.
Small and shallow lakes response to atmospheric conditions veryfast.
Accurate estimation of the heat transfer between the atmosphereand water is extremely important to model the temperaturedynamics and stratification in the lakes.
1-D & 2-D models are not able to consider horizontal advectionterm in morphometrically complex lakes and reservoirs
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Outline
1 IntrouductionAims of the study
2 Lake BinabaDescriptionWhy 3D-CFD Model?
3 CFD ModelCFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
4 ConclusionConclusion
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
CFD Work Flow
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Geometry
The starting point for all problems is a “geometry”.
Figure: Geometry of lake using in CFD model(V.S:100)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Equations
Continuity equation(mass is conserved):
∂uj∂xj
= 0 (1)
Momentum equations using Boussinesq approach
∂ui∂t
+∂
∂xj(ujui)−
∂
∂xj
{νeff
[(∂ui∂xj
+∂uj∂xi
)− 2
3
(∂uk∂xk
)δij
]}= − ∂p
∂xi+ gi [1 − β(T − Tref )]
(2)
Temperature(energy is conserved) in the water body
∂T
∂t+
∂
∂xj(Tuj) − κeff
∂
∂xk(∂T
∂xk) = ST (3)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Equations
In the model, for incompressible flows the density is calculated asa linear function of temperature as:
ρk = 1 − β (T − Tref ) (4)
Incoming shortwave radiation is included in the source term(ST ).
ST (z∗, t) =1
ρ0CpηI0 exp(−ηz∗) (5)
This function allows the radiation to be absorbed through a finitedistance in the upper layers of the model water column ratherthan only at the air-water interface.
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Boundary Conditions
Wind over water surface affects lake currents, sensible and latentheat fluxes.
Shear Stress BC(U):
τsurf,u = ρ0
((νt + ν)
∂u
∂z
)(6)
τsurf,v = ρ0
((νt + ν)
∂v
∂z
)(7)
For Temperature, the water surface temperature is not needed.
Using a mixed(implicit) BC (T):
ρ0Cp
(κeff
∂T
∂z
)surf
= Hnet (8)
Hnet = HLA +HLW +HS +HE (9)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
OpenFOAM
OpenFOAM: Open Source Field Operation andManipulation
Open-Source Library
Free of Charge
Running in LINUX OS
C++ Library
Linking with PYTHON
New solvers and BCs can be implemented by the user
Running in parallel on distributed processors(tested for up to1000 cores)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Results
Figure: Bathymetry of Lake Binaba
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Results
Figure: Simulated velocity in the lake(t=3930 sec)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Results
0
50
100
150
200
250
300
350
0 20000 40000 60000 80000 100000 120000 140000 160000 180000
Late
nt H
eat F
lux[W
m-2
]
Time(s)
minHlat
maxHlat
aveHlat
Figure: Calculated latent heat flux over water surface(simple case)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Results
-20
-15
-10
-5
0
5
10
15
20
25
30
0 20000 40000 60000 80000 100000 120000 140000 160000 180000
Sensib
le H
eat F
lux[W
m-2
]
Time(s)
minHS
maxHS
aveHS
Figure: Calculated sensible heat flux over water surface(simple case)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Results
-350
-300
-250
-200
-150
-100
-50
0
0 20000 40000 60000 80000 100000 120000 140000 160000 180000
Net H
eat F
lux[W
m-2
]
Time(s)
minHnet
maxHnet
aveHnet
Figure: Calculated net heat flux over water surface(simple case)
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IntrouductionLake BinabaCFD ModelConclusion
CFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
Results
9.35e+15
9.4e+15
9.45e+15
9.5e+15
9.55e+15
9.6e+15
9.65e+15
9.7e+15
9.75e+15
0 20000 40000 60000 80000 100000 120000 140000 160000 180000
Heat S
tora
ge[J
]
Time(s)
SumHStorage
Figure: Calculated heat storage of water body (simple case)
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IntrouductionLake BinabaCFD ModelConclusion
Conclusion
Outline
1 IntrouductionAims of the study
2 Lake BinabaDescriptionWhy 3D-CFD Model?
3 CFD ModelCFD Work FlowGeometrySolvingUsing OpenFOAMResults and Post-processing
4 ConclusionConclusion
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IntrouductionLake BinabaCFD ModelConclusion
Conclusion
Conclusion
Computational fluid dynamics (CFD) analysis has proven to be avaluable design tool in the water resources
Modelling is one of the best means to gain understanding ofcomplex flow fields
Wind over water surface affects lake currents, sensible and latentheat fluxes
Buoyancy effect due to density gradiant in water body should beconsidered in temperature profile
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IntrouductionLake BinabaCFD ModelConclusion
Conclusion
Questions?
Thanks for your attention
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