boundary layer meteorology - university of reading...
TRANSCRIPT
Boundary Layer Meteorology The wind that shakes the buildings
Prof. Janet F. Barlow Department of Meteorology Director Technologies for
Sustainable Built Environments (TSBE) Centre
University of Reading
Today’s talk
A brief history of turbulence and wind engineering A framework for urban boundary layers Recent research findings in London
A history of BL turbulence and wind engineering
• 1904 Prandtl: Fluid flow in very little friction
• 1935 Pagon: 8 papers on aerodynamics in civil engineering
• 1941 Kolmogorov: -5/3 power law for spectrum
• 1946 Obukhov: length defined for surface layer
• 1950 von Karman: applications of aerodynamics in engineering
• 1954 Monin Obukhov similarity theory published
• 1961 AmSocCivEng: 6 papers on “wind actions on structures”
• 1961 Davenport: model of wind-excited behaviour of structures
• 1963 1st Int Symp on Wind Effects on Buildings and Structures (Teddington, UK)
• 1968 Kansas experiment: established surface layer theory predictions
• 1970 BLM journal started
• 1971 Businger et al: flux profile results
• 1972 Kaimal et al: spectral results for varying stabilities
• 1973 Minnesota experiment: mixed layer scaling demonstrated for BLayer
• 1974 Willis and Deardorff: mixed layer scaling deduced from lab experiments
• 1980 JWEIA started
The Kansas Experiment, 1968
Shellard, 1963 conf paper
X zobs zeff
To do
Davenport 1963 conf discussion
Wind profile over different surfaces
Davenport. 1963 conf paper
Wind profiles over inhomogeneous surfaces
Framework for the urban boundary layer: Scale Heterogeneity Roughness sublayer Canopy-like turbulence (?) Urban “units” Packing density and roughness
Effect of urban area on wind profile
Plate and Kiefer (2001)
Different scales of the Urban Boundary Layer
Building, H
Street canyon, H/W
Internal Boundary Layer, zIBL
Urban Boundary Layer, zi
Street 10-100m
Neighbourhood 100-1000m
City 1-10km
Kastner-Klein and Rotach 2004
Urban roughness sublayer
U(z)
z
H
3H
Wind profiles in RSL
Mixing layer hypothesis (Raupach et al 1996)
• Inflection point in mean wind profile unstable, leads to growth of coherent structures
• Responsible for mixing throughout vegetation canopy depth
• Turbulence highly efficient (e.g. Ruw > surface layer values)
Coherent structures: urban field study evidence
• Quadrant analysis and skewness profiles:
sweeps dominate within canopy, ejections above
• Feigenwinter et al. (2005) in Basel
• Ensemble averaged coherent structure
• Ejection-sweep cycle
• Temperature microfront
Coherent structures: deductions from DNS
• Consensus not yet reached about coherent structures over urban surfaces – form, generation
Coceal et al. 2007c: “cartoon”
Oke, 1988
H/W = 0.6
H/W = 1.0
Isolated roughness H/W < 0.3
Skimming flow H/W > 0.65
Wake interference 0.3 < H/W < 0.65
Street canyon flow
Frontal area index f : Frontal area/lot area Plan area index p : Plan area/lot area
Defining packing density
Roughness parameters depend on packing density
London’s packing density
Padhra 2010, PhD thesis
London-based research projects
DAPPLE (2002-2009) – street level dispersion
REPARTEE (2006-2007) – vertical pollutant distribution
ACTUAL (2009-2014) – building design interactions with urban climate at a range of scales
ClearfLo (2010-2013) – air quality at city scale
River Thames
1.6 km Westminster City Council
rooftop
BT Tower
Regent’s Park
Hyde Park
1.6 km
Barlow et al. 2011 JWEIA
Cities are collections of relatively short streets between intersections - the classical street canyon is a rarity.
DAPPLE
www.dapple.org.uk
Arnold et al. 2004, STOTEN
Westminster City Council
rooftop
2004 campaign BT Tower NE wind direction
Led by A. Robins Barlow et al. 2009 BLM
Wood et al. 2009, BAMS
Funded under the Challenging Engineering programme (2009 – 2014) www.actual.ac.uk
BT Tower at
190 m
Roof
top at
~20m
NEW
urban
sodar
<200m
Doppler lidar
90m < z < 2000m
ACTUAL: observing flow at range of scales
Barlow et al. 2009 BLM
Wood et al. 2010 BLM
Helfter et al. 2011 ACP
Barlow et al. 2011 ACP
Barlow et al. 2011 JWEIA
Bradley and Barlow,
ISARS conf 2012
Wood et al. 2012 STOTEN
KCL: Scintillometers
(various heights)
Grimmond et al.
1.6 km Westminster City Council
rooftop
BT Tower
Regent’s Park
Hyde Park River Thames
1.6 km
KCL rooftop
• Room next to busy road (~3600 veh hr-1)
• Use ambient pollution (NOx) as a tracer to monitor ventilation rate
How do urban winds and temperatures drive building infiltration?
Aidan Brocklehurst, PhD
with Stuart Upton (BRE)
• Lag of indoor concentrations ~ 4 hours
• Infiltration rate driven strongly by wind direction
What is the evolution of winds along an urban river throughout a day?
Wood et al. 2012, STOTEN Curtis Wood, post-doc (now FMI)
Collaboration with Sue Grimmond et al. at KCL
• C – cloudy, S – sunny
• Feb to May 2011 • New horizontal scanning
lidar technique
• Comparison with sonic anemometry, scintillometer
4 11
Dan Drew, post-doc
• Doppler lidar observed wind-speed using Doppler beam swinging (DBS)
• Comparison with BT winds: Ulidar=0.98 UBT + 0.56
• Sampling error ~ 0.4 ms-1
L
LiDAR gate resolution
Lane S.E. et al., 2013. JWEIA
How well do Doppler lidar measured wind-speeds compare with mast-based measurements?
0.2 0.4 0.6 0.8 1 1.2
(a) (b)
0.2 0.4 0.6 0.8 1 1.2
(a) (b)
How do measured UBL wind profiles compare with ESDU non-equilibrium model?
• 1km square roughness length map for London
• MacDonald (1998) applied to LUCID building morphology
• Roughness length along transect
• WCC to London Heathrow
• Black: morphology
• Red: land use proxy (Cook 1997)
Drew et al., subm. JWEIA
• Lidar wind-speed profile, U > U75 (1052 hours): red
• Urban morphology roughness: black circles
• Land use proxy: black stars
How do measured BL wind profiles compare with meteorological models?
• Unified Model (UM), 1.5km resolution, M. Best heat flux scheme
• Forecast model (blue), lidar (red)
• 22:00 UHI, strong jet present
Sian Lane, PhD
CASE award Met Office
Conclusions
• Homogeneous boundary layers (reasonably!) well understood
• Inhomogeneous BL’s – much focus on urban
• Combination of methods yields best insight
• New remote sensing techniques well suited to UBL investigations
Where do the research challenges lie?
Low wind conditions
Stability effects
Low carbon building design
Green infrastructure
Cities as “laboratories”