HARMO17, Budapest, 9 12 May, 2016.€¦ · London South Bank University, Imperial College London...
Transcript of HARMO17, Budapest, 9 12 May, 2016.€¦ · London South Bank University, Imperial College London...
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Mesh Adaptive LES for micro-scale air pollution dispersion and effect of tall buildings.
Elsa Aristodemou, Luz Maria Boganegra, Christopher Pain, Alan
Robins, and Helen ApSimon
HARMO17, Budapest, 9 – 12 May, 2016.
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Outline
• Motivation/Combined Heat &
Power plant emissions
• The Wind tunnel Experiments
• Large Eddy Simulation within
the FLUIDITY software
• Validation case
• Additional LES cases
• The “Walkie-Talkie” simulation (if there is time)
• Conclusions
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
C: Exhibition
Building
A: The
Garden
Building
E: Melbury Building
B: Park
Building
D: High
Street
Building
G: Park
Close
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
The Enflo Wind Tunnel Geometry (Robins, 2013)
Working section: 20 x 3.5 x 1.5 m
(Length x Width x Height)
Overall length: 27.2 m
Geometry of interest was at the scale of
1:200.
Several Cases were run. We look at
First case, with All buildings in place.
• Generates neutral, stable and unstable
boundary layers
• Has three dimensional, computer
controlled traversing gears, tracer
supply systems, calibration facilities, a
turntable and extensive condition
monitoring.
• Operates under full computer control,
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A
C
E
D
B
G
F
The Geometry within the FLUIDITY software
plan view with adaptive mesh Wind Tunnel
Case Case1
Block Height
(m)
A 0.1428
B 0.1238
C 0.1315
D 0.1228
E 0.0971
F 0.0315
G 0.1152
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
4 m long
2 m
wide
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Initial Tehtrahedral Mesh (GMSH pre-processor) as
input in the FLUIDITY software
This mesh is subsequently adapted, based on certain metrics
associated with physical parameters: velocity and concentrations:
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Adaptive Mesh
Final Number of Elements ~ 1,000,000 ; No of nodes: ~ 175,000
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Additional
FLUIDITY
cases:
Cases 2 and 3
Block Normal
Case1
Tall
Case2
Taller
Case3
A 0.1428 0.1428 0.1428
B 0.1238 0.4 0.4
C 0.1315 0.4 0.4
D 0.1228 0.4 0.4
E 0.0971 0.2 0.2
F 0.0315 0.2 0.2
G 0.1152 0.25 0.6
Case 2 - Tall
Case 3 – Taller
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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Results presented on three planes
Vertical XZ- plane: Through centre of domain
Vertical YZ- plane : Through centre of domain
Horizontal XY- plane At Height of Source
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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Mesh-adaptive LES within the FLUIDITY software (http://fluidityproject.github.io/) Pain et al. http:/www.amcg.th.ic.ac.uk
• Unstructured finite element mesh - Adaptive anisotropic elements, efficiently representing boundary layers and anisotropic flow features.
• Allows resolution in the domain where needed (e.g. streets) with spatially variable max & min anisotropic element length scales, as well as interpolation errors.
• adaptive mesh to resolve what we are interested in e.g. the pollutant concentrations.
• Adaptive mesh allows representation of moving objects (e.g. vehicles, pedestrians) using a 2-phase fluid approach.
• Parallel mesh-adaptivity for large scale problems; up to 100k processors – on powerful supercomputers.
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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Large Eddy Simulation (LES)
with sub-grid modelling (1) Filtered Navier-Stokes with Smagorinsky sub-grid model:
12( )i i
j t ij
j i j
u u pu v v S
t x x x
Anisotropic
Eddy
Viscosity nt
that depends
on Variable
filter width
D, where:
D = 2*local
element size
(hz,hh,hx).
( ) ( )( )j j
j j j
c cu cD cu cu
t x x x
(2) Filtered Advection-Diffusion for a passive scalar
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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• Resolved flow field: numerically solved.
• Sub-filter scales: modelled using a
• Smagorisnky-type Subgrid scale model.
i
j
j
i
ijx
u
x
uS
~~
2
1~2
2( )
t S
t S
v l S
v C S
D
Cs=Smagorinsky constant = 0.11
D=variable filter width: dependent on the element lengths
Large Eddy Simulation (LES) with sub-grid modelling
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Anisotropic
Eddy
Viscosity nt
that depends
on Variable
filter width D,
where:
D = 2*local
element size
(hz, hh, hx).
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Plan view of Lines where Detectors are
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Validation: Wind Tunnel Case – Mean Concentrations
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Location of Source
X
(m)
Y
(m)
Z
(m)
-0.01875 0.01875 0.1508
Detectors higher
than the source
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Validation: Wind Tunnel Case – Mean Concentrations
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Location of Source
X
(m)
Y
(m)
Z
(m)
-0.01875 0.01875 0.1508
Detectors higher
than the source
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
…and…..just to show that not all is “perfect”!
Location of Source
X
(m)
Y
(m)
Z
(m)
-0.01875 0.01875 0.1508
Detectors below
the source
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Velocity field at near ground level – H=0.065m
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
What is the effect of High Buildings on Dispersion?
London, UK, cityscape is changing
fast with a large number of high
buildings being developed.
Hence, motivation to study the effect of
such high buildings on the dispersion
of air pollutants.
The “infamous” Walkie-Talkie building
Capturing the detailed
turbulent flow field
Detailed turbulent flow
field near the top
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London South Bank University, Imperial College
London and University of Surrey, HARMO17,
Budapest 2016
Building Height effect on Velocities
A F
F
A
G
D
D G
X-Z Vertical Plane
Wind tunnel Case: Case 1
Taller Buildings: Case 3
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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Effect of Building Height on Velocities
Wind Tunnel Case: Case 1
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Tall buildings: Case 2
Taller buildings: Case 3
Horizontal X-Y plane
at Source Height
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…and to do justice to the results:
a clearer image for Case 3
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London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Effect of the instantaneous flow field on dispersion
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Building Height effect on Velocity Vectors X-Z Vertical Plane
Taller-Buildings: Case 2
G F
A
D
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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Effect of Building Height on the Turbulent flow field X-Z Vertical Plane
G F A
D
Taller-Buildings: Case 3
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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London South Bank University, Imperial College
London and University of Surrey, HARMO17,
Budapest 2016
Building Height effect on Tracer Dispersion X-Z Vertical Plane
Wind tunnel case: Case 1
Taller buildings: Case 3
A
F
A F
D G
G
D
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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London South Bank University, Imperial College
London and University of Surrey, HARMO17,
Budapest 2016
Building Height effect on Tracer Dispersion X-Z Vertical Plane
Taller buildings: Case 3
Taller buildings: Case 2
A D F G
A
F
G
D
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
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Effect of Building Height on the Turbulent flow field Y-Z Vertical Plane
Wind tunnel case: Case 1
Taller Buildings: Case 3
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Velocity contours and Velcocity vectors
Y-Z plane
Vertical
Movement
Noticeable
Above the building
Where source is.
This movement is
Responsible for
The upward lifting of
The pollutant, seen
In the next slide.
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Wind tunnel case: Case 1
Taller Buildings: Case 3
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
Effect on Dispersion : Y-Z Vertical Plane
Taller Buildings: Case 3
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Summary/Conclusions
London South Bank University, Imperial College London and University of Surrey, HARMO17, Budapest 2016
• Validation still in progress but so far very promising
• At the micro-scale levels, detailed CFD modelling with
high resolution meshes is very important in determining
path of contaminants
• Optimal building design/height (in particular): CFD can
show some unexpected outcomes – as Case 3 showed.
Thank you for your attention
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Acknowledgements
Although of course already as co-authors on this work, still special
thanks to:
• Prof Christopher Pain: for the development of the FLUIDITY,
without whose support this innovative mesh-adaptive CFD work
could not be achieved.
• Prof Alan Robins: for the provision of the wind tunnel data and
fruitful discussions on their interpretation.
• My two past Master students at LSBU: (i) Carlos Andres Bernal
Castro, for the set-up of the Walkie-Talkie geometry and (ii) Luz
Maria Valencia Boganegra for the wind-tunnel geometry.