Description of the UCP
description
Transcript of Description of the UCP
Implementation and Evaluation of a New Drag and Length Scale
Parameterization in the Multilayer Urban Canopy Parameterization of
WRFA.Simón-Moral1*, A. Martilli1, J. L. Santiago1, S.
Krayenhoff2
[email protected] dept, Research Centre for Energy, Environment and
Technology (CIEMAT), Madrid, Spain1
Department of Geography, University of British Columbia, Vancouver, Canada2
Page 214th Annual WRF User's Workshop
24 – 28 JUNE 2013
Description of the UCP
• The Building Effect Parameterization (BEP, Martilli et al. 2002) solves the effect on the flow caused by the buildings inside a city
• Building drag: – Sinks for momentum
– Source of TKE
– At the moment Cd=0.4 (Raupach, 1992)
• Turbulent transport and dissipation– Turbulent diffusion coefficients
– Turbulence dissipation
• Temperature and Radiation– Radiation trapping
– Energy balance in each surface
VortortdD SUUCWindF )(
VortdD SUCTKEF
3)(
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TKEC
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HeatTurbulenceMomentum
Drag Wake diffusion Radiation
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Motivation
• From Computational Fluid Dynamics (CFD) simulations over aligned configurations of cubes new features are observed– Drag coefficient depends on the configuration of the buildings
– Length scales depends on the density of buildings
• A new parameterization derived from CFD results for the Cd and the length scales considering different configurations of buildings is presented
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Methodology
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Drag Parameterization
• Different values for the Cd have been found from different aligned configurations of cubes with different packing densities (λ
p).
• Cd is parameterized as constant value with height, by means of the
distance between buildings in the directions parallel and perpendicular to the wind, represented by:– Sheltering factor λs=Wx/H
– Channelling factor λc=Wy/By
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Drag Parameterization
Sheltering Channelling Interaction
λch= 1
λch= 1,83λch= 1.31
λch= 2λch= 3
λch= 1,83λch= 1.31
λch= 2λch= 3
λch= 1
Parameterization
CFD Values
λs
Page 714th Annual WRF User's Workshop
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• The length scale is found to depend on the packing density of the configurations
• According to its behaviour, three zones are observed:– Le/Ce=α1·(h-d) for z/h<1– Le/Ce=α1·(z-d) for 1<z/h<1.5– Le/Ce=α2·(z-d2) for z/h>1.5 Where α1= 2.19 and α2=1.2 and d2 is calculated in order to guarantee
continuity• Displacement height is calculated by means of the packing
density λp as:
• Lk is calculated by:
where Ci are model constants
15.0/ pHd
Length Scales Parameterization
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• Distinguish between different configurations with same λp.
• Relative differences between configurations well reproduced
• Better results are found for U field inside canopy.
• TKE mean value is well reproduced, although
– There is an overestimation
at canopy heigth – Different shape
• underestimation of Km and <u’w’> inside canopy
• U, is mainly characterized by Cdrag
Column Model Test
Page 914th Annual WRF User's Workshop
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• The parameterizations are introduced in BEP, already implemented in WRF
• 3d ideal city is simulated in order to test the improvement• Simulation set-up:
– Square city rounded by rural area
– Domain: 100x100x51
– City: 10x10, centred in the domain
– dx = dy = 1000m
– dt = 2s
– Boundary conditions: Open
– Coriolis force used
Implementation in WRF
Page 1014th Annual WRF User's Workshop
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Results
Page 11
• Night– Larger Cd in New version
• Larger drag effect, lower wind– Larger length scales
• Enhancement of the vertical mixing
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Old VS New Comparison
Temperature Wind
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• Day– Larger Cd in New version
• Larger drag effect, lower wind– Larger length scales up to 1.5 H
• Upward propagation of the perturbation and enhancement of vertical mixing
– Lower length scales over 1.5 H• Downdward propagation from high levels
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Old VS New Comparison
Temperature Wind
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• Turbulent Kinetic Energy– Combination of C
d, U, dU/dz & dT/dz
– Cd
TKE U TKE dU/dz TKE– K
m dT/dz TKE
Old VS New Comparison
NIGHT DAY
Page 1414th Annual WRF User's Workshop
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• New parameterization is able to distinguish between configurations
New Parameterization Skills
λp=0.125
1) λs=1.83, λch=1.832) λs=3, λch=13) λs=1, λch=3
λs=1
1) λp=0.25, λch=12) λp=0.125, λch=33) λp=0.167, λch=2
λch=1
1) λp=0.25, λs=12) λp=0.125, λs=33) λp=0.33, λs=0,5
Page 1514th Annual WRF User's Workshop
24 – 28 JUNE 2013
• A new parameterization for drag coefficient and length scales is presented and implemented in BEP
• The new drag coefficient depends on the buildings configuration
• New Length scales for turbulence are parameterized as a function of the packing density λp
• The new parameterization is able to distinguish between different configurations
• Future work: – Find easily measurable urban parameters to implement in
BEP– Generalize the parameterization for different shape buildings
Conclusions
Thank you very much for your attention!Thank you very much for your attention!
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