Hydrodynamic Simulation of Shallow Lakes

IntroductionCase Study: Lake Binaba

Simulation ProcessResults of Simulation

Conclusion

Temperature Dynamics Investigation at Small andShallow Lakes Using Hydrodynamic Model

Ali AbbasiNick van de Giesen

Delft University of TechnologyWater Resources Management

August 20, 2014

A. Abbasi & N.C. van de Giesen TUDelft Temperature Dynamics at Small and Shallow Lakes HIC2014



Conclusion

Motivations

Outline

1 IntroductionMotivations

2 Case Study: Lake BinabaDescription

3 Simulation ProcessCFD WorkflowGeometry & MeshingSolving

4 Results of SimulationResults

5 ConclusionConclusion




Conclusion

Motivations

MotivationsPredicting the temperature profile in reservoirs and lakes?

Inland water bodies are very important parts of the continental landsurface.

Water temperature dynamics can have a profound effect in heatstorage of lakes and water quality.

Heat storage of lakes and reservoirs is essential to estimateevaporation.

measurements of heat exchange between the atmosphere and watersurface are sparse.

Vertical resolution of available experiments often are not sufficientfor assessing small-scale turbulence effects

Water temperature is affected by radiative forcing, air temperatureand wind velocity.

Temperature profile in reservoirs and lakes related to the both ofwater quantity and water quality.




Conclusion

Motivations

Why 3-D Model?

Transport processes in water body are inherently three-dimensional:

driven by wind over water surface, surface thermodynamics andtopography of lake.

the non-linearity of some terms in the heat transfer expression at theair-water interface(no analytic solution)

one-dimensional models are not able to consider horizontal advectionterm.

2-D models are not able to capture mechanisms affectingtemperature transport and mixing accurately, specially inmorphometrically complex lakes and reservoirs

Prediction of the flow field and temperature dynamics is possibleonly through fully 3-D models.

Representation of the boundary geometry in shallow lakes is morecritical that the deep lakes.




Conclusion

Motivations

The Aims of Study

To develop a three-dimensional time-dependent hydrodynamic andheat 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 compute total heat storage of shallow lakes in order to estimateevaporation from water surface.




Conclusion

Description

Outline









Conclusion

Description

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




Conclusion

Description

LocationLake Binaba:

Figure: Location of lake Binaba




Conclusion

Description

Location

Lake Binaba:

Figure: Location of lake Binaba(Google earth)




Conclusion

CFD WorkflowGeometry & MeshingSolving

Outline









Conclusion


CFD WorkflowUsing powerful, open-source and free of charge tools:

Geometry Meshing Case Setup & Solving

PostProcessing

Point CloudQGIS

ArcMapSalome

Free-CADMeshLabadMesh

BlockMeshSnappyHexMesh

SalomeEngridGMSH

TETGENGridGEN

OpenFOAM

ParaFoamParaviewGnuplotPython

Matplotlib

Up to 60% of User TimeUp to 20% of User

Time

Up to 20% of User

Time




Conclusion


Geometry

Preparing geometry of lake includes following steps:

1 Reading the initial point cloud (x,y,z coordinates from text file)

2 Improving the point cloud by interpolating.

3 Generating the STL(STereoLithography) file

4 Cleaning & reapairing the STL file

5 Preparing the STL file to input to the mesh generator




Conclusion


GeometryReading the initial point cloud (x,y,z coordinates from text file):

It includes only 642 points.

This number of points are not sufficient to produce a precisegeometry of lake

(vertical exaggerated by 100)




Conclusion


GeometryImproving the point cloud by interpolating:

Improved point cloud includes only 68’802 points.Adding extra points to define the water surface boundary in desiredelevation.Using QGIS( or ArcMap to interpolating points)





Conclusion


GeometryGenerating & Cleaning the STL(STereoLithography) file:

Using MeshLab to produce the water & bottom surfaces.Using MeshLab & adMesh to repair the surfaces.Using QGIS( or ArcMap to interpolating points)





Conclusion


GeometryFinally, Have a nice surface to generate CFD mesh:





Conclusion


GeometryFlexible for different water levels:

Max depth= 4.0 m (vertical exaggerated by 100)




Conclusion


MeshingFinally, using ’ SnappyHexMesh to generate CFD mesh





Conclusion


Governing EquationsThe flow field in a morphometrically complex small lake is solved with theincompressible RANS(Reynolds Averaged Navier-Stokes) equations:

Continuity Equations∂uj∂xj

= 0,

Momentum Equation

∂ui∂t

+∂

∂xj(ujui)−

∂

∂xj

{νeff

[(∂ui∂xj

+∂uj∂xi

)− 2

3

(∂uk∂xk

)δij

]}= − ∂p

∂xi+ gi [1− β(T − Tref )]

Temperature Equation

∂T

∂t+

∂

∂xj(Tuj)− αeff

∂

∂xk(∂T

∂xk) = ST (z, t)




Conclusion


Turbulence Model

Selecting realizable k − ε turbulence model:

∂k

∂t+ uj

∂k

∂xj=

∂

∂xj

[(ν +

νTσk

)∂k

∂xj

]+ νT

(∂ui∂xj

+∂uj∂xi

)∂ui∂xj

− ε+GB +Gk+Sk(t, u2)

∂ε

∂t+ uj

∂ε

∂xj=

∂

∂xj

(νTσε

∂ε

∂xj

)+ C1Sε− Cε2

ε2

k +√νε

+ Cε1Cε3ε

kGB + Sε(t, u2)




Conclusion


Temperature B.CAt the water surface the heat diffused away from the lake surface equals

the net surface:

ρ0C p(αeff∂T∂ z

)=H net

H net=H LA+H LW+H S+HE

Water Surface

H E=hm×ρa(X s−X a)×(24×3600×28.4)

hm=0.0016252×U 2+0.0007712

H S=hs (T s−T a)

hs=2.1954×U 2+1.0419

H LA=(1−rA)Eair×σT air4

Eair=1.24×(1+0.17C2)(ea

T air

)17 H LW=−Ew×σT w

4

time, relative humidity, wind speed, air temperature, water surface temperature

time, relative humidity,

wind speed, air temperature, water surface

temperature

time, Relative humidity air temperature,

Atmosphere condition

time, water surface Temperature,Atmosphere condition

Incoming shortwave radiation is included in

the source term

ST (z ,t )=1

ρ0C p

η I 0 exp(−η z)

I 0=(1−r a) I Sinc




Conclusion


Velocity B.CAt the water surface the effects of wind speed should be considered:

Two different approach

For velocity B.C

Water Surface

ux≠0,∂ ux

∂ z=0 ,

u y≠0 ,∂u y

∂ z=0, uz=0

Sk=u✴

3

κ zSε=C1ε

εk

Sk

u✴=√τ0

ρ0

τ0=ρaCDU 102=ρau✴

2

CD ,10=[κ−1ln (

10gC D, 10U10

2 )+11.3 ]−2

Implementing the effect of wind speed in

turbulence equations(as source terms)

[νt∂u∂ z

]=τsxρ0

[νt∂u∂ z

]=τsx

ρ0

τsx=ρaCDuw √uw2+vw

2

τsy=ρaCD vw √uw2 +vw

2

uz=0

wind shear stress as Time-dependent shear stress

boundary condition over the water surface




Conclusion


Boundary Condition

Time-dependent parameters over the water surface:




Conclusion


Boundary Condition

Time-dependent parameters over the water surface:




Conclusion


OpenFOAM

OpenFOAM: Open Source Field Operation and Manipulation

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




Conclusion

Results

Outline









Conclusion

Results

ResultsVelocity distribution(x) over the water surface(t=10 hr)




Conclusion

Results

Results

Vector velocity over the water surface(t=10 hr)




Conclusion

Results

Results

Temperature values over the water surface(t=10 hr)




Conclusion

Results

ResultsStream lines in the water body(t=10 hr)




Conclusion

Results

ResultsTemperature distribution on a vertical section(t=10 hr):




Conclusion

Results

ResultsTemperature distribution on a vertical section(t=32 hr):




Conclusion

Results

Results

Comparing the temperature values in probe location:




Conclusion

Conclusion

Outline









Conclusion

Conclusion

Conclusion

CFD is a powerful tool in analysing and designing water resourcesissues.

Shallow lakes responce fast to atmospheric parameters.

Wind speeds over the water surface can effect significantly the flowpattern in water body.

Temperature profiles in water body are affected by circulation andflow field in water body.

3-D CFD model could be a very powerful tool to simulatetemperature dynamics in shallow lakes.




Conclusion

Conclusion

Thanks

Thanks for your attention




Conclusion

Conclusion

Questions?

More details: [email protected]

11th International Conference on Hydroinformatics(HIC 2014)August 2014

New York City, USA


Date post:	19-Jun-2015
Category:	Engineering
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Hydrodynamic Simulation of Shallow Lakes

Engineering