dsd-int 2016 mixing of a thermal plume in a highly stratified artificial urban pond - csibran
TRANSCRIPT
Mixing of a thermal plume in a highly stratified artificial
urban pond
A. Csibrán, T. Krámer and P. Torma
Budapest University of Technology and Economics, Department of Hydraulic and Water Resources Engineering, Budapest, Hungary
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Preliminary
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• Located in the heart of Budapest
• Inflow from a thermal bath • High stratification
• Bad water quality
Hydraulically dead zones?
3D thermodynamic modelling
The lake
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• Average water depth ≈ 1 meter
• Average lake temperature in winter ≈ 20.5 °C
• Steady inflow • 3500 m3/day, 32 °C
• Through a pipe at lower layers
• Surrounded by trees • Low wind stress on surface
Grid
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• Constraints of a curvilinear grid • Boundary-fitted and near-orthogonal
• 20 layers (sharp vertical gradients)
• 7600x20 cells
• Cell area: from 0.1 m2 to 5 m2
Grid
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• Constraints of a curvilinear grid • Boundary-fitted and near-orthogonal
• 20 layers (sharp vertical gradients)
• 7600x20 cells
• Cell area: from 0.1 m2 to 5 m2
Grid
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• Constraints of a curvilinear grid • Boundary-fitted and near-orthogonal
• 20 layers (sharp vertical gradients)
• 7600x20 cells
• Cell area: from 0.1 m2 to 5 m2
Validation
Validation in winter period Average air temperature during the simulation: 6.6 °C
Relatively long time simulation (7 days) Uncertain initial conditions
Objective to reproduce Shape of the thermal plume
Vertical temperature profiles (gradients)
Flow field
Primarily attempted to validate the turbulence model
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Validation: Shape of the plume
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Validation: Temperature profiles
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• 16 vertical profiles
• High Precision Thermometer
• At 4 depths • 0.05 m
• 0.25 m
• 0.45 m
• 0.65 m
Validation: Temperature profiles II.
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Validation: Temperature profiles III.
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Validation: Velocities
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• Nortek Vectrino Doppler • Suitable for low velocity
measurements
• 25 Hz
• 19 points
• At 0.25 m depth
• 1.5-2 m from the shore
Validation: Velocities II.
Flow field at 0.25 m depth
: Modelled
: Measured
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Validation: Velocities II.
Flow field at 0.25 m depth
: Modelled
: Measured
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Validation: Velocities III.
Flow field at 0.25 m depth
: Modelled
: Measured
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Mixed layer depth
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Mixed layer depth
0.2 °C
• Depth, where the difference
between maximum and
minimum temperatures is less
than 0.2 °C
• Describes stratification in every
point
Water age
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• Modelled as a conservative
tracer
• Advection-diffusion process
• The concentration of the tracer
within the inflow is decreased
by one unit each hour
Representation of stratification and water exchange
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How to improve water quality by hydrodynamics?
Different vertical deflector wall configurations
Passive and cheap solution
It has been proposed for similarly functioning cooling ponds
Circulation system?
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Wall configurations
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Wall configurations: Mixed layer depth
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Wall configurations: Water age
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Summary
The model was suitable to resolve low Reynolds number thermodynamics in a shallow setting Sharp gradients resolved
Through the use of water age we have revealed the zones where the water exchange is slower
We attempted to improve the water exchange by deflector walls however those did not influence the conditions significantly
In the near future we may consider to apply a circulation system in the model and test its impact
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Thank you for your attention!
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