Introuduction Lake Binaba Lake Modeling Conclusion
CFD Modeling of Shallow and SmallLakes
(Case Study: Lake Binaba)
Ali AbbasiNick van de Giesen
Department of Water ManagementDelft University of Technology
November 28, 2013
Ali Abbasi — CFD Modeling of Shallow and Small Lakes (Case Study: Lake Binaba) 1/48
Introuduction Lake Binaba Lake Modeling Conclusion
1 IntrouductionWhat is CFD?Why CFD?Where is CFD Used?Numerical MethodsModelingFlow Conditions
2 Lake BinabaDescriptionAims of the study
3 Lake ModelingCFD ModelPre-processingSolving the Flow FieldPost-processing
4 ConclusionConclusion
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Introuduction Lake Binaba Lake Modeling Conclusion
1 IntrouductionWhat is CFD?Why CFD?Where is CFD Used?Numerical MethodsModelingFlow Conditions
2 Lake BinabaDescriptionAims of the study
3 Lake ModelingCFD ModelPre-processingSolving the Flow FieldPost-processing
4 ConclusionConclusion
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Introuduction Lake Binaba Lake Modeling Conclusion
What is CFD?
CFD : Computational Fluid DynamicsThe result of the confluence of fluid dynamics and a rangeof allied subjects:
Numerical MethodsGrid GenerationComputational GeometryComputer-aided Geometric DesignComputer GraphicsParallel Computing
Simulation of fluid engineering systems using modeling andnumerical methodsAnalytical Fluid Dynamics(AFD) and Experimental FluidDynamics(EFD)
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Introuduction Lake Binaba Lake Modeling Conclusion
Why CFD?
Analysis and design:more cost effective and more rapid than EFDCFD provides high-fidelity database for diagnosting flowfield
Simulation of physical fluid phenomena that are difficultfor experiments:
full scale simulationsenvironmental effects(wind, weather, etc.)hazards (explosions, pollution)physics (plantetary boundary layer)
Knowledge and exploration of flow physics.
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Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
AerospaceAutomotiveBiomedicalHydraulicsMarineOil & GasPower generation...
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Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 1 : Smoothing the cap over a swimmers head significantly improveshydrodynamic performance
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Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 2 : Fishway optimization: a numerical modeling study
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Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 3 : CFD: a valuable design tool in water resources
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Introuduction Lake Binaba Lake Modeling Conclusion
Where is CFD Used?
Figure 4 : CFD modeling of water flow in a basin
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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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Introuduction Lake Binaba Lake Modeling Conclusion
Numerical Methods
The continuous Initial Boundary Value Problems(IBVPs)are discretized into algebraic equations using numericalmethodsnumerical methods include:
Discretization methodSolvers and numerical parametersGrid generation and transformationHigh performance computation(HPC) and post-processing
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Introuduction Lake Binaba Lake Modeling Conclusion
Modeling
Modeling is the mathematical physics problem formulationin terms of continuous initial boundary valueproblem(IBVPs)IBVP is in the form of Partial DifferentialEquations(PDEs) with appropriate boundary conditionsand initial conditions.Modeling includes:
Geometry and domain(simple and complex geometry, sizeand shape)CoordinatesGoverning equationsFlow conditionsInitial and boundary conditionsselect on of models for different applications
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Introuduction Lake Binaba Lake Modeling Conclusion
Flow Conditions
Based on the physics of the fluids phenomena, CFD can bedistinguished 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 flowThermal/density effects(Pr)etc.
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Introuduction Lake Binaba Lake Modeling Conclusion
1 IntrouductionWhat is CFD?Why CFD?Where is CFD Used?Numerical MethodsModelingFlow Conditions
2 Lake BinabaDescriptionAims of the study
3 Lake ModelingCFD ModelPre-processingSolving the Flow FieldPost-processing
4 ConclusionConclusion
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Introuduction Lake Binaba Lake Modeling Conclusion
Description
Lake Binaba:Location: an artificial lake located in northern GhanaSurface: the average area of the lake surface is 4.5 km2
Average depth: only 3 mMaximum depth: 7 mUsage: a small reservoir, used as a form of infrastructure
for the provision of waterAir temperature: fluctuates between 24 C and 35 CWater surface temperature: varies from 28 C to 33 CClimate: (semi-)arid region
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Introuduction Lake Binaba Lake Modeling Conclusion
DescriptionLocation
Lake Binaba
Figure 6 : Lake Binaba in Ghana
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Introuduction Lake Binaba Lake Modeling Conclusion
DescriptionLocation
Lake Binaba
Figure 7 : Location of lake Binaba(Google earth)
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Introuduction Lake Binaba Lake Modeling Conclusion
Aims of the study
To develop a three-dimensional time-dependenthydrodynamic and heat transfer model(CFD model)Simulating the effects of wind and atmosphere conditionsover a complex bathymetryTo predict the circulation patterns as well as thetemperature distribution in the water bodyTo compute total heat storage of small shalow lakes andreservoirs in order to estimate evaporation from watersurface
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Introuduction Lake Binaba Lake Modeling Conclusion
1 IntrouductionWhat is CFD?Why CFD?Where is CFD Used?Numerical MethodsModelingFlow Conditions
2 Lake BinabaDescriptionAims of the study
3 Lake ModelingCFD ModelPre-processingSolving the Flow FieldPost-processing
4 ConclusionConclusion
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Introuduction Lake Binaba Lake Modeling Conclusion
CFD Model
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Figure 8 : CFD simulation workflow
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processing
Main steps in preparing the bathymetry of lake to use in CFDmodeling:
Reading initial point cloud (x,y,z coordinates from text file)Adding extra points in point cloud to improve thegenerated STL fileGenerating the STL fileCleaning & reapairing the STL fileGenerating the computational mesh or CFD mesh
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingReading 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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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingAdding extra points in point cloud to improve the generated STL file
Adding extra points to define the water surfaceAdding extra points to improve the bathymetryUsing ArcMap to interpolate between points
Figure 10 : Improved point cloud: 68802 points (x,y,z)(V.S:100)
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingGenerating the STL file
STL (STereoLithography) format is similar to a TIN,except it defines the shell of a volume with a set ofinterlocking triangular facests:facet normal ni nj nk
outer loopvertex v1x v1y v1zvertex v2x v2y v2zvertex v3x v3y v3z
endloopendfacet
UsingMeshLab(free and open-source STL generator)
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingGenerating the STL file
Figure 11 : STL file from meshLab(V.S:100)
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingCleaning the STL file
The generated STL file should be clean to can be used inCFD modelingUsing addmesh (free and open-source STL cleaner)
Figure 12 : Final STL file(V.S:100)
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingSeperating Boundaries
Water surfaceBottom and sides of lake
Figure 13 : Final geometry used in meshing(V.S:100)
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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingGenerating the computational mesh or CFD mesh
Refinig the mesh near the boundariesnPoints: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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Introuduction Lake Binaba Lake Modeling Conclusion
Pre-processingChecking 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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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldEquations
Continuity equation:
∂uj∂xj
= 0, (1)
Momentum equations using Boussinesq approach
(2)
∂ui∂t + ∂
∂xj(ujui)
− ∂
∂xj
{νeff
[(∂ui∂xj
+ ∂uj∂xi
)− 2
3
(∂uk∂xk
)δij
]}=
− ∂p∂xi
+ gi [1 − β(T − Tref )]
Temperature in the water body
∂T∂t + ∂
∂xj(Tuj) − κeff
∂
∂xk(∂T∂xk
) = ST (3)
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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldInitail Conditions
ICs should not affect final resultsOnly affect the number of iterations to reach convergedsolution
Figure 16 : Initial condition for T
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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldBoundary Conditions
Temperature
ρ0Cp
(κeff
∂T∂z
)surf
= Hnet (4)
Velocity
τsurf ,u = ρ0
((νt + ν)∂u
∂z
)(5)
τsurf ,v = ρ0
((νt + ν)∂v
∂z
)(6)
τsurf ,u = CDρair(v2
10 + u210
)12 .u10 (7)
τsurf ,v = CDρair(v2
10 + u210
)12 .v10 (8)
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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldMeteorogical measurements
0 10 20 30 40 5015
20
25
30
35
40
T[C]
Tair
Twater−surface
0 10 20 30 40Time[hr]
−400
−200
0
200
400
600
800
1000
HeatF
luxes[W
/m
2]
HLA
HLW
Hns
HS
HE
Hnet
Rs
Figure 17 : Time-dependent parameters using as B.C
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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldMeteorogical measurements
Figure 18 : Time-dependent parameters using as B.C
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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldSolver
Open Source Field Operation and Manipulation(OpenFOAM)
Open-Source LibraryFree of Chargein LINUXC++ LibraryLinking with PYTHON
Special Issuenew SOLVERS and UTILITIES Can be Created byUSERS
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Introuduction Lake Binaba Lake Modeling Conclusion
Solving the Flow FieldRunning in parallel
OF runs in parallelWe need to run the model in parallelDecomposing the domain accoeding to the availabe sourcesUsing MPIOF was tested at least for 1000 cores!Using GPU
Lake BinabaWe are running the model on 64 and 36 nodes
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processing
Figure 19 : Bathymetry of lake Binaba
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingVelocity
Figure 20 : Velocity in t=3930 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingVelocity
Figure 21 : Velocity in t=3930 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingTemperature
Figure 22 : Temperature in t=3930 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingSource term in T
Figure 23 : Temperature source term in t=3930 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingVelocity
Figure 24 : Velocity in t=5640 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingTemperature
Figure 25 : Temperature in t=5640 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
Post-processingVelocity
Figure 26 : Velocity in t=7440 s (V.S:10)
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Introuduction Lake Binaba Lake Modeling Conclusion
1 IntrouductionWhat is CFD?Why CFD?Where is CFD Used?Numerical MethodsModelingFlow Conditions
2 Lake BinabaDescriptionAims of the study
3 Lake ModelingCFD ModelPre-processingSolving the Flow FieldPost-processing
4 ConclusionConclusion
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Introuduction Lake Binaba Lake Modeling Conclusion
Conclusion
CFD modeling and graphical output provides a detailedvisual representation of the modeled systemModel results provides a high degree of confidence forproject owners, designers, and other stakeholdersComputational fluid dynamics (CFD) analysis has provento be a valuable design tool in the water resourcesModelling is one of the best means to gain understandingof complex flow fieldsWind over water surface affects lake currents, sensible andlatent heat fluxesBuoyancy effect due to density gradiant in water bodyshould be considerd in temperature profile
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