© 2022 IIETA. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
OPEN ACCESS
Precise prediction of air quality in a street canyon under diverse conditions could be established through the comprehensive validation of velocity of wind profiles and the concentration distribution of pollutants. In this study, a two-step approach was developed using Computational Fluid Dynamics simulations. The first step involved the validation of wind velocity profiles obtained using wind tunnel experimental measurements of an isolated street canyon discussed in ref. [1], while the second step focused on the validation of dispersion of pollutants from wind tunnel measurements discussed in ref. [2] conducted on isolated and urban street canyons. The wind velocity profiles obtained at five distinct vertical planes between the leeward and windward walls in the wind tunnel study [1] were validated by simulating the 2D cross-section of the entire wind tunnel domain with high accuracies; R2 values of 0.931–0.986 were obtained across the canyon depth. The concentration distribution of the pollutant in the wind tunnel study [2] were validated for a range of velocities (0.5, 1, 2 and 4 m/s) using both 2D and 3D models. A verification of the Reyn- olds independent nature of the flow was performed by comparing the wind tunnel and street scale models and suitability of employing K-e turbulence model with Enhanced Wall Treatment and K-ε Low Reynolds Number Model for the wind tunnel scale, and Standard Wall Functions for the street scale were observed. A 2D simulation of urban street canyon flow representing the whole wind tunnel cross-section in the flow direction was also studied to observe repetitive flow nature and thereby a potential to employ fully developed flow conditions for the same. The urban street canyon flow is established through the means of fully developed periodic flow profiles, which inherently restricts the additional mass sources in the flow domain. The emission scenario in the fully developed flow was captured by means of flow profile mapping at the upwind edge of the leeward building. To estimate the minimum number of downwind canyons required to keep up the fully developed flow profile at the target street canyon, a parameterization of the same was per- formed. Finally, the validation of the concentration profiles was obtained with parameterization of the Schmidt number, and an optimal Schmidt number was obtained in the case of using Realizable K-e turbulence model. The developed and validated methodology provides a robust and efficient means of modelling air pollution dispersion in the isolated and urban street canyons for future research investigations.
2D and 3D simulations, CFD, fully developed flows, isolated street canyon, urban street canyon, validation
[1] Kovar-Panskus, A., Louka, P., Sini, J.F., Savory, E., Czech, M., Abdelqari, A., Mestayer,P.G. & Toy, N., Influence of geometry on the mean flow within urban street canyons–acomparison of wind tunnel experiments and numerical simulations. Water, Air and SoilPollution: Focus, 2(5), pp. 365–380, 2002. https://doi.org/10.1007/978-94-010-0312-4_26
[2] Meroney, R.N., Pavageau, M., Rafailidis, S. & Schatzmann, M., Study of line sourcecharacteristics for 2-D physical modelling of pollutant dispersion in street canyons.Journal of Wind Engineering and Industrial Aerodynamics, 62(1), pp. 37–56, 1996.https://doi.org/10.1016/s0167-6105(96)00057-8
[3] Landrigan, P.J., Fuller, R., Acosta, N.J., Adeyi, O., Arnold, R., Baldé, A.B., Bertollini,R., Bose-O’Reilly, S., Boufford, J.I., Breysse, P.N. & Chiles. T., The Lancet Commissionon pollution and health. The Lancet, 391(10119), pp. 462–512, 2018. https://doi.org/10.1016/s0140-6736(17)32345-0
[4] McNabola, A., Broderick, B.M. & Gill. L.W., A numerical investigation of the impactof low boundary walls on pedestrian exposure to air pollutants in urban street canyons.Science of the Total Environment, 407(2), pp. 760–769, 2009. https://doi.org/10.1016/j.scitotenv.2008.09.036
[5] Gallagher, J., Gill, L.W. & McNabola, A., Optimizing the use of on-street car parkingsystem as a passive control of air pollution exposure in street canyons by largeeddy simulation. Atmospheric Environment, 45(9), pp. 1684–1694, 2011. https://doi.org/10.1016/j.atmosenv.2010.12.059
[6] Gromke, C., Buccolieri, R., Di Sabatino, S. & Ruck, B., Dispersion study in a streetcanyon with tree planting by means of wind tunnel and numerical investigations–evaluationof CFD data with experimental data. Atmospheric Environment, 42(37), pp. 8640–8650, 2008. https://doi.org/10.1016/j.atmosenv.2008.08.019
[7] Kastner-Klein, P. & Plate, E.J., Wind-tunnel study of concentration fields in streetcanyons. Atmospheric Environment, 33(24–25), pp. 3973–3979, 1999. https://doi.org/10.1016/s1352-2310(99)00139-9
[8] Mirzai, M.H., Harvey, J.K. & Jones, C.D., Wind tunnel investigation of dispersion ofpollutants due to wind flow around a small building. Atmospheric Environment, 28(11),pp. 1819–1826, 1994. https://doi.org/10.1016/1352-2310(94)90321-2
[9] Allegrini, J., Dorer, V. & Carmeliet, J., Buoyant flows in street canyons: validation ofCFD simulations with wind tunnel measurements. Building and Environment, 72, pp.63–74, 2014. https://doi.org/10.1016/j.buildenv.2013.10.021
[10] Sagrado, A.P., van Beeck, J., Rambaud, P. & Olivari, D., Numerical and experimentalmodelling of pollutant dispersion in a street canyon. Journal of Wind Engineering andIndustrial Aerodynamics, 90(4–5), pp. 321–339, 2002. https://doi.org/10.1016/s0167-6105(01)00215-x
[11] Chang, C.H. & Meroney, R.N., Concentration and flow distributions in urban streetcanyons: wind tunnel and computational data. Journal of Wind Engineering and IndustrialAerodynamics, 91(9), pp. 1141–1154, 2003. https://doi.org/10.1016/s0167-6105(03)00056-4
[12] Meroney, R.N., Leitl, B.M., Rafailidis, S. & Schatzmann, M., Wind-tunnel and numericalmodeling of flow and dispersion about several building shapes. Journal of WindEngineering and Industrial Aerodynamics, 81(1–3), pp. 333–345, 1999. https://doi.org/10.1016/s0167-6105(99)00028-8
[13] Llaguno-Munitxa, M., Bou-Zeid, E. & Hultmark, M., The influence of building geometryon street canyon air flow: validation of large eddy simulations against wind tunnelexperiments. Journal of Wind Engineering and Industrial Aerodynamics, 165, pp.115–130, 2017. https://doi.org/10.1016/j.jweia.2017.03.007
[14] Ding, S., Huang, Y., Cui, P., Wu, J., Li, M. & Liu, D., Impact of viaduct on flow reversionand pollutant dispersion in 2D urban street canyon with different roof shapes-Numerical simulation and wind tunnel experiment. Science of the Total Environment,671, pp. 976–991, 2019. https://doi.org/10.1016/j.scitotenv.2019.03.391
[15] Gromke, C. & Ruck, B., Influence of trees on the dispersion of pollutants in an urbanstreet canyon—experimental investigation of the flow and concentration field.Atmospheric Environment, 41(16), pp. 3287–3302, 2007. https://doi.org/10.1016/j.atmosenv.2006.12.043
[16] Gromke, C., A vegetation modeling concept for building and environmental aerodynamicswind tunnel tests and its application in pollutant dispersion studies. EnvironmentalPollution, 159(8–9), pp. 2094–2099, 2011. https://doi.org/10.1016/j.envpol.2010.11.012
[17] Cui, P.Y., Li, Z. & Tao, W.Q., Investigation of Re-independence of turbulent flow andpollutant dispersion in urban street canyon using numerical wind tunnel (NWT) models.International Journal of Heat and Mass Transfer, 79, pp. 176–188, 2014. https://doi.org/10.1016/j.ijheatmasstransfer.2014.07.096
[18] Heist, D.K., Perry, S.G. & Brixey, L.A., A wind tunnel study of the effect of roadwayconfigurations on the dispersion of traffic-related pollution. Atmospheric Environment,43(32), pp. 5101–5111, 2009. https://doi.org/10.1016/j.atmosenv.2009.06.034
[19] Kovar-Panskus, A, Louka, P., Mestayer, P.G., Savory, E., Sini, J.F. & Toy, N., Influenceof geometry on the flow and turbulence characteristics within urban street canyons–Intercomparison of wind tunnel experiments and numerical simulations. InProceedings of the 3rd International Conference on Urban Air Quality (pp. 19–23),2001.
[20] Chan, T.L., Dong, G., Leung, C.W., Cheung, C.S. & Hung, W.T., Validation of a twodimensionalpollutant dispersion model in an isolated street canyon. Atmospheric environment,36(5), pp. 861–872, 2002. https://doi.org/10.1016/j.atmosenv.2009.06.034
[21] Takano, Y. & Moonen, P., On the influence of roof shape on flow and dispersion in anurban street canyon. Journal of Wind Engineering and Industrial Aerodynamics, 123,pp. 107–120, 2013. https://doi.org/10.1016/j.jweia.2013.10.006
[22] Franke, J., Best practice guideline for the CFD simulation of flows in the urban environment.Meteorological Inst., 2007.