2017 |
Kent, Christoph; Grimmond, Sue; Gatey, David Aerodynamic roughness parameters in cities: Inclusion of vegetation (Journal Article) Journal of Wind Engineering and Industrial Aerodynamics, Volume 169 , pp. 168-176, 2017. (Abstract | Links | BibTeX | Tags: Aerodynamic roughness length, Drag coefficient for vegetation, Logarithmic wind profile, Morphometric method, urban, Zero-plane displacement) @article{Kent2017b, title = {Aerodynamic roughness parameters in cities: Inclusion of vegetation}, author = {Christoph Kent and Sue Grimmond and David Gatey}, editor = {Journal of Wind Engineering & Industrial Aerodynamics}, url = {http://urbanfluxes.eu/wp-content/uploads/2018/01/2017_Kent_et_al_JWEIA.pdf}, year = {2017}, date = {2017-10-01}, journal = {Journal of Wind Engineering and Industrial Aerodynamics}, volume = {Volume 169}, pages = {168-176}, abstract = {A widely used morphometric method (Macdonald et al. 1998) to calculate the zero-plane displacement (zd) and aerodynamic roughness length (z0) for momentum is further developed to include vegetation. The adaptation also applies to the Kanda et al. (2013) morphometric method which considers roughness-element height variability. Roughness-element heights (mean, maximum and standard deviation) of both buildings and vegetation are combined with a porosity corrected plan area and drag formulation. The method captures the influence of vegetation (in addition to buildings), with the magnitude of the effect depending upon whether buildings or vegetation are dominant and the porosity of vegetation (e.g. leaf-on or leaf-off state). Application to five urban areas demonstrates that where vegetation is taller and has larger surface cover, its inclusion in the morphometric methods can be more important than the morphometric method used. Implications for modelling the logarithmic wind profile (to 100 m) are demonstrated. Where vegetation is taller and occupies a greater amount of space, wind speeds may be slowed by up to a factor of three}, keywords = {Aerodynamic roughness length, Drag coefficient for vegetation, Logarithmic wind profile, Morphometric method, urban, Zero-plane displacement}, pubstate = {published}, tppubtype = {article} } A widely used morphometric method (Macdonald et al. 1998) to calculate the zero-plane displacement (zd) and aerodynamic roughness length (z0) for momentum is further developed to include vegetation. The adaptation also applies to the Kanda et al. (2013) morphometric method which considers roughness-element height variability. Roughness-element heights (mean, maximum and standard deviation) of both buildings and vegetation are combined with a porosity corrected plan area and drag formulation. The method captures the influence of vegetation (in addition to buildings), with the magnitude of the effect depending upon whether buildings or vegetation are dominant and the porosity of vegetation (e.g. leaf-on or leaf-off state). Application to five urban areas demonstrates that where vegetation is taller and has larger surface cover, its inclusion in the morphometric methods can be more important than the morphometric method used. Implications for modelling the logarithmic wind profile (to 100 m) are demonstrated. Where vegetation is taller and occupies a greater amount of space, wind speeds may be slowed by up to a factor of three |
Kent, Christoph; Grimmond, Sue; Barlow, Janet; Gatey, David; Kotthaus, Simone; Lindberg, Fredrik; Halios, Christos Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas (Journal Article) Boundary-Layer Meteorol (2017) 164:183–213, Vol: 164(2) , pp. 183-213, 2017. (Abstract | Links | BibTeX | Tags: Aerodynamic roughness length, Anemometric methods, Logarithmic wind-speed profile, Morphometric methods, Source area, Zero-plane displacement) @article{Kent2017, title = {Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas}, author = {Christoph Kent and Sue Grimmond and Janet Barlow and David Gatey and Simone Kotthaus and Fredrik Lindberg and Christos Halios}, editor = {Boundary-Layer Meteorology}, url = {http://urbanfluxes.eu/wp-content/uploads/2018/01/2017_Kent_et_al_BLM.pdf}, doi = {10.1007/s10546-017-0248-z}, year = {2017}, date = {2017-04-28}, journal = {Boundary-Layer Meteorol (2017) 164:183–213}, volume = {Vol: 164(2)}, pages = {183-213}, abstract = {Nine methods to determine local-scale aerodynamic roughness length (z0) and zero-plane displacement (zd ) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial zd and z0 estimates. Across the three sites, zd varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating zd is consistently greater than the local mean building height. Depending upon method and wind direction, z0 varies between 0.1 and 5 m with morphometric z0 consistently being 2–3 m larger than the anemometric z0. No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine zd and z0}, keywords = {Aerodynamic roughness length, Anemometric methods, Logarithmic wind-speed profile, Morphometric methods, Source area, Zero-plane displacement}, pubstate = {published}, tppubtype = {article} } Nine methods to determine local-scale aerodynamic roughness length (z0) and zero-plane displacement (zd ) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial zd and z0 estimates. Across the three sites, zd varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating zd is consistently greater than the local mean building height. Depending upon method and wind direction, z0 varies between 0.1 and 5 m with morphometric z0 consistently being 2–3 m larger than the anemometric z0. No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine zd and z0 |
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