Abstract
We experimentally investigate the effect of a typical building covering: the gable roof, on the flow and air exchange in urban canyons. In general, the morphology of the urban canopy is very varied and complex, depending on a large number of factors, such as building arrangement, or the morphology of the terrain. Therefore we focus on a simple, prototypal shape, the two-dimensional canyon, with the aim of elucidating some fundamental phenomena driving the street-canyon ventilation. Experiments are performed in a water channel, over an array of identical prismatic obstacles representing an idealized urban canopy. The aspect ratio, i.e. canyon-width to building-height ratio, ranges from 1 to 6. Gable roof buildings with 1:1 pitch are compared with flat roofed buildings. Velocity is measured using a particle-image-velocimetry technique with flow dynamics discussed in terms of mean flow and second- and third-order statistical moments of the velocity. The ventilation is interpreted by means of a simple well-mixed box model and the outflow rate and mean residence time are computed. Results show that gable roofs tend to delay the transition from the skimming-flow to the wake-interference regime and promote the development of a deeper and more turbulent roughness layer. The presence of a gable roof significantly increases the momentum flux, especially for high packing density. The air exchange is improved compared to the flat roof buildings, and the beneficial effect is more significant for narrow canyons. Accordingly, for unit aspect ratio gable roofs reduce the mean residence time by a factor of 0.37 compared to flat roofs, whereas the decrease is only by a factor of 0.9 at the largest aspect ratio. Data analysis indicates that, for flat roof buildings, the mean residence time increases by 30% when the aspect ratio is decreased from 6 to 2, whereas this parameter is only weakly dependent on aspect ratio in the case of gable roofs.
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References
Amicarelli A, Leuzzi G, Monti P (2012) Lagrangian micromixing models for concentration fluctuations: an overview. Am J Environ Sci 8:577–590. https://doi.org/10.3844/ajessp.2012.577.590
Badas MG, Ferrari S, Garau M, Querzoli G (2017) On the effect of gable roof on natural ventilation in two-dimensional urban canyons. J Wind Eng Ind Aerodyn 162:24–34. https://doi.org/10.1016/j.jweia.2017.01.006
Barlow JF, Harman IN, Belcher SE (2004) Scalar fluxes from urban street canyons. Part I: laboratory simulation. Boundary-Layer Meteorol 113:369–385. https://doi.org/10.1007/s10546-004-6204-8
Bendat JS, Piersol AG (2011) Random data: analysis and measurement procedures. Wiley, Hoboken
Bentham T, Britter R (2003) Spatially averaged flow within obstacle arrays. Atmos Environ 37:2037–2043. https://doi.org/10.1016/S1352-2310(03)00123-7
Besalduch LA, Badas MG, Ferrari S, Querzoli G (2013) Experimental studies for the characterization of the mixing processes in negative buoyant jets. EPJ Web Conf 45:01012. https://doi.org/10.1051/epjconf/20134501012
Besalduch LA, Badas MG, Ferrari S, Querzoli G (2014) On the near field behavior of inclined negatively buoyant jets. EPJ Web Conf 67:02007. https://doi.org/10.1051/epjconf/20146702007
Blocken B, Janssen WD, van Hooff T (2012) CFD simulation for pedestrian wind comfort and wind safety in urban areas: general decision framework and case study for the Eindhoven University campus. Environ Model Softw 30:15–34. https://doi.org/10.1016/j.envsoft.2011.11.009
Brown MJ, Lawson RE, DeCroix DS, Lee RL (2000) Mean flow and turbulence measurements around a 2-D array of buildings in a wind tunnel. In: 11th joint AMS/AWMA conference on the applications of air pollution meteorology. Long Beach, CA
Carrasco-Hernandez R, Smedley ARD, Webb AR (2015) Using urban canyon geometries obtained from Google Street View for atmospheric studies: potential applications in the calculation of street level total shortwave irradiances. Energy Build 86:340–348. https://doi.org/10.1016/j.enbuild.2014.10.001
Castro IP, Robins AG (1977) The flow around a surface-mounted cube in uniform and turbulent streams. J Fluid Mech 79:307–335. https://doi.org/10.1017/S0022112077000172
Cheng WC, Liu C-H (2011) Large-eddy simulation of flow and pollutant transports in and above two-dimensional idealized street canyons. Boundary-Layer Meteorol 139:411–437. https://doi.org/10.1007/s10546-010-9584-y
Di Bernardino A, Monti P, Leuzzi G, Querzoli G (2014) A laboratory investigation of flow and turbulence over a twodimensional urban canopy. In: Proceedings of the 16th international conference on harmonisation within atmospheric dispersion modelling for regulatory purposes, Varna, Bulgaria, 8–11 September, pp 432–436
Di Bernardino A, Monti P, Leuzzi G, Querzoli G (2015) Water-channel study of flow and turbulence past a two-dimensional array of obstacles. Boundary-Layer Meteorol 155:73–85. https://doi.org/10.1007/s10546-014-9987-2
Fackrell JE (1984) Parameters characterising dispersion in the near wake of buildings. J Wind Eng Ind Aerodyn 16:97–118. https://doi.org/10.1016/0167-6105(84)90051-5
Falchi M, Querzoli G, Romano GP (2006) Robust evaluation of the dissimilarity between interrogation windows in image velocimetry. Exp Fluids 41:279–293. https://doi.org/10.1007/s00348-006-0148-3
Fallah-Shorshani M, Shekarrizfard M, Hatzopoulou M (2017) Integrating a street-canyon model with a regional Gaussian dispersion model for improved characterisation of near-road air pollution. Atmos Environ 153:21–31. https://doi.org/10.1016/j.atmosenv.2017.01.006
Fernando HJS, Lee SM, Anderson J, Princevac M, Pardyjak E, Grossman-Clarke S (2001) Urban fluid mechanics: air circulation and contaminant dispersion in cities. Environ Fluid Mech 1:107–164. https://doi.org/10.1023/A:1011504001479
Ferrari S, Badas MG, Garau M, Querzoli G, Seoni A (2017) The air quality in narrow two-dimensional urban canyons with pitched and flat roof buildings. Int J Environ Pollut (in press)
Florens E, Eiff O, Moulin F (2013) Defining the roughness sublayer and its turbulence statistics. Exp Fluids 54:1500. https://doi.org/10.1007/s00348-013-1500-z
Goulart EV, Coceal O, Branford S, Thomas TG, Belcher SE (2016) Spatial and temporal variability of the concentration field from localized releases in a regular building array. Boundary-Layer Meteorol 159:241–257. https://doi.org/10.1007/s10546-016-0126-0
Harman IN, Finnigan JJ (2007) A simple unified theory for flow in the canopy and roughness sublayer. Boundary-Layer Meteorol 123:339–363. https://doi.org/10.1007/s10546-006-9145-6
Ho Y-K, Liu C-H, Wong MS (2015) Preliminary study of the parameterisation of street-level ventilation in idealised two-dimensional simulations. Build Environ 89:345–355. https://doi.org/10.1016/j.buildenv.2015.02.042
Huang Y, Jin M, Sun Y (2007) Numerical studies on airflow and pollutant dispersion in urban street canyons formed by slanted roof buildings. J Hydrodyn Ser B 19:100–106. https://doi.org/10.1016/S1001-6058(07)60034-1
Husain SZ, Bélair S, Mailhot J, Leroyer S (2013) Improving the representation of the nocturnal near-neutral surface layer in the urban environment with a mesoscale atmospheric model. Boundary-Layer Meteorol 147:525–551. https://doi.org/10.1007/s10546-013-9798-x
Immer M, Allegrini J, Carmeliet J (2016) Time-resolved and time-averaged stereo-PIV measurements of a unit-ratio cavity. Exp Fluids 57:101. https://doi.org/10.1007/s00348-016-2186-9
Janssen WD, Blocken B, van Hooff T (2013) Pedestrian wind comfort around buildings: comparison of wind comfort criteria based on whole-flow field data for a complex case study. Build Environ 59:547–562. https://doi.org/10.1016/j.buildenv.2012.10.012
Jiang D, Jiang W, Liu H, Sun J (2008) Systematic influence of different building spacing, height and layout on mean wind and turbulent characteristics within and over urban building arrays. Wind Struct Int J 11:275–289
Jiménez J (2004) Turbulent flows over rough walls. Annu Rev Fluid Mech 36:173–196. https://doi.org/10.1146/annurev.fluid.36.050802.122103
Kastner-Klein P, Rotach MW (2004) Mean flow and turbulence characteristics in an urban roughness sublayer. Boundary-Layer Meteorol 111:55–84. https://doi.org/10.1023/B:BOUN.0000010994.32240.b1
Liu C-H, Wong CCC (2014) On the pollutant removal, dispersion, and entrainment over two-dimensional idealized street canyons. Atmos Res 135–136:128–142. https://doi.org/10.1016/j.atmosres.2013.08.006
Liu C-H, Leung DYC, Barth MC (2005) On the prediction of air and pollutant exchange rates in street canyons of different aspect ratios using large-eddy simulation. Atmos Environ 39:1567–1574. https://doi.org/10.1016/j.atmosenv.2004.08.036
Llaguno-Munitxa M, Bou-Zeid E, Hultmark M (2017) The influence of building geometry on street canyon air flow: validation of large eddy simulations against wind tunnel experiments. J Wind Eng Ind Aerodyn 165:115–130. https://doi.org/10.1016/j.jweia.2017.03.007
Macdonald RW, Griffiths RF, Hall DJ (1998a) An improved method for the estimation of surface roughness of obstacle arrays. Atmos Environ 32:1857–1864. https://doi.org/10.1016/S1352-2310(97)00403-2
Macdonald RW, Griffiths RF, Hall DJ (1998b) A comparison of results from scaled field and wind tunnel modelling of dispersion in arrays of obstacles. Atmos Environ 32:3845–3862. https://doi.org/10.1016/S1352-2310(98)80006-X
Martinuzzi R, Tropea C (1993) The flow around surface-mounted, prismatic obstacles placed in a fully developed channel flow (data bank contribution). J Fluid Eng 115:85–92. https://doi.org/10.1115/1.2910118
Michioka T, Takimoto H, Ono H, Sato A (2016) Effect of fetch on a mechanism for pollutant removal from a two-dimensional street canyon. Boundary-Layer Meteorol 160:185–199. https://doi.org/10.1007/s10546-016-0136-y
Monti P, Leuzzi G (1996) A closure to derive a three-dimensional well-mixed trajectory-model for non-Gaussian, inhomogeneous turbulence. Boundary-Layer Meteorol 80:311–331. https://doi.org/10.1007/BF00119421
Neophytou MK-A, Markides CN, Fokaides PA (2014) An experimental study of the flow through and over two dimensional rectangular roughness elements: deductions for urban boundary layer parameterizations and exchange processes. Phys Fluids 1994–Present 26:086603. https://doi.org/10.1063/1.4892979
Ngan K, Lo KW (2016) Revisiting the flow regimes for urban street canyons using the numerical Green’s function. Environ Fluid Mech 16:313–334. https://doi.org/10.1007/s10652-015-9422-3
Nosek Š, Kukačka L, Kellnerová R, Jurčáková K, Jaňour Z (2016) Ventilation processes in a three-dimensional street canyon. Boundary-Layer Meteorol 159:259–284. https://doi.org/10.1007/s10546-016-0132-2
Oke TR (1988) Street design and urban canopy layer climate. Energy Build 11:103–113. https://doi.org/10.1016/0378-7788(88)90026-6
Pelliccioni A, Monti P, Leuzzi G (2015) An alternative wind profile formulation for urban areas in neutral conditions. Environ Fluid Mech 15:135–146. https://doi.org/10.1007/s10652-014-9364-1
Pelliccioni A, Monti P, Leuzzi G (2016) Wind-speed profile and roughness sublayer depth modelling in urban boundary layers. Boundary-Layer Meteorol 160:225–248. https://doi.org/10.1007/s10546-016-0141-1
Perret L, Blackman K, Fernandes R, Savory E (2017) Relating street canyon vertical mass-exchange to upstream flow regime and canyon geometry. Sustain Cities Soc 30:49–57. https://doi.org/10.1016/j.scs.2017.01.001
Perry AE, Joubert PN (1963) Rough-wall boundary layers in adverse pressure gradients. J Fluid Mech 17:193–211. https://doi.org/10.1017/S0022112063001245
Rafailidis S (1997) Influence of building areal density and roof shape on the wind characteristics above a town. Boundary-Layer Meteorol 85:255–271. https://doi.org/10.1023/A:1000426316328
Reynolds RT, Castro IP (2008) Measurements in an urban-type boundary layer. Exp Fluids 45:141–156. https://doi.org/10.1007/s00348-008-0470-z
Rosten E, Drummond T (2006) Machine learning for high-speed corner detection. In: Computer vision—ECCV 2006. Springer, Berlin, pp 430–443
Simón-Moral A, Santiago JL, Krayenhoff ES, Martilli A (2014) Streamwise versus spanwise spacing of obstacle arrays: parametrization of the effects on drag and turbulence. Boundary-Layer Meteorol 151:579–596. https://doi.org/10.1007/s10546-013-9901-3
Sini J-F, Anquetin S, Mestayer PG (1996) Pollutant dispersion and thermal effects in urban street canyons. Atmos Environ 30:2659–2677. https://doi.org/10.1016/1352-2310(95)00321-5
Snyder WH (1979) Guideline for fluid modeling of atmospheric diffusion. Environmental Protection Agency tech. rep, Research Triangle Park, NC (USA)
Song J, Wang Z-H (2015) Interfacing the urban land-atmosphere system through coupled urban canopy and atmospheric models. Boundary-Layer Meteorol 154:427–448. https://doi.org/10.1007/s10546-014-9980-9
Soulhac L, Salizzoni P, Cierco F-X, Perkins R (2011) The model SIRANE for atmospheric urban pollutant dispersion; part I, presentation of the model. Atmos Environ 45:7379–7395. https://doi.org/10.1016/j.atmosenv.2011.07.008
Sousa JMM, Pereira JCF (2004) DPIV study of the effect of a gable roof on the flow structure around a surface-mounted cubic obstacle. Exp Fluids 37:409–418. https://doi.org/10.1007/s00348-004-0830-2
Takano Y, Moonen P (2013) On the influence of roof shape on flow and dispersion in an urban street canyon. J Wind Eng Ind Aerodyn 123, Part A:107–120. https://doi.org/10.1016/j.jweia.2013.10.006
Tominaga Y, Akabayashi S, Kitahara T, Arinami Y (2015) Air flow around isolated gable-roof buildings with different roof pitches: wind tunnel experiments and CFD simulations. Build Environ 84:204–213. https://doi.org/10.1016/j.buildenv.2014.11.012
Tuna BA, Tinar E, Rockwell D (2013) Shallow flow past a cavity: globally coupled oscillations as a function of depth. Exp Fluids 54:1586. https://doi.org/10.1007/s00348-013-1586-3
Uehara K, Wakamatsu S, Ooka R (2003) Studies on critical Reynolds number indices for wind-tunnel experiments on flow within urban areas. Boundary-Layer Meteorol 107:353–370. https://doi.org/10.1023/A:1022162807729
Vincent JH (1967) Model experiments on the nature of air pollution transport near buildings. Atmos Environ 11:765–774. https://doi.org/10.1016/0004-6981(77)90186-X
Weitbrecht V, Socolofsky SA, Jirka GH (2008) Experiments on mass exchange between groin fields and main stream in rivers. J Hydraul Eng 134:173–183. https://doi.org/10.1061/(ASCE)0733-9429(2008)134:2(173)
Xie X, Huang Z, Wang J (2005) Impact of building configuration on air quality in street canyon. Atmos Environ 39:4519–4530. https://doi.org/10.1016/j.atmosenv.2005.03.043
Yassin MF (2011) Impact of height and shape of building roof on air quality in urban street canyons. Atmos Environ 45:5220–5229. https://doi.org/10.1016/j.atmosenv.2011.05.060
Zajic D, Fernando HJS, Calhoun R, Princevac M, Brown MJ, Pardyjak E (2010) Flow and turbulence in an urban canyon. J Appl Meteorol Climatol 50:203–223. https://doi.org/10.1175/2010JAMC2525.1
Zajic D, Fernando HJS, Brown MJ, Pardyjak ER (2015) On flows in simulated urban canopies. Environ Fluid Mech 15:275–303. https://doi.org/10.1007/s10652-013-9311-6
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This work was funded by the University of Cagliari.
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Garau, M., Badas, M.G., Ferrari, S. et al. Turbulence and Air Exchange in a Two-Dimensional Urban Street Canyon Between Gable Roof Buildings. Boundary-Layer Meteorol 167, 123–143 (2018). https://doi.org/10.1007/s10546-017-0324-4
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DOI: https://doi.org/10.1007/s10546-017-0324-4