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Suitability of using carbon dioxide as a tracer gas for studying vehicle emission dispersion in a real street canyon 认领 引用
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作者 Yuhan Huang Helen B.Wang +10 位作者 Hilda M.W.Mak Mengyuan Chu Zhi Ning Bruce Organ Edward F.C.Chan Chun-Ho Liu Wai-Chuen Mok Christof Gromke Ho Kyong Shon Chengwang Lei John L.Zhou 《Journal of Environmental Sciences》 SCIE EI CAS CSCD 2025年第9期832-845,共14页
High-rise buildings form deep urban street canyons and restrict the dispersion of vehicle emissions,posing severe health risks to the public by aggravating roadside air quality.Field measurements are important for und... High-rise buildings form deep urban street canyons and restrict the dispersion of vehicle emissions,posing severe health risks to the public by aggravating roadside air quality.Field measurements are important for understanding the dispersion process of tailpipe emissions in street canyons,while a major challenge is the lack of a suitable tracer gas.Carbon dioxide(CO2),which is safe to the public and inexpensive to obtain,can be reliably measured by existing gas analysers.This study investigated the suitability of using CO2as a tracer gas for characterising vehicle emission dispersion in a real-world street canyon.The tracer gas was released via a line or point source,whose dispersion was characterised by a sensors network comprising low-cost air quality sensors.The results showed that the CO2contained in the exhaust gas of a test vehicle itself had unmeasurable effect at roadsides.Both the line and point sources produced obvious CO2level elevations at approximately 30 s after the test vehicle passed by.In addition,for both line and point sources,the CO2elevations were much more distinct at the roadside next to tailpipe exit than the opposite side,and were higher at 0.8 m than 1.6 m above the ground.The present study demonstrated that using CO2as a tracer gas is feasible for investigating vehicle emission dispersion in real-world street canyons.Future studies are needed to improve the gas release rate of the developed tracer gas systems for more reliable measurements and larger street canyons. 展开更多
关键词 Vehicle emission dispersion Tracer gas Carbon dioxide Urban street canyon Line emission source Point emission source
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Computational fluid dynamics simulation of the wind flow over an airport terminal building 认领 引用 被引量：8
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作者 Chun-ho LIU Dennis Y.C.LEUNG +1 位作者 Alex C.S.MAN P.W.CHAN 《Journal of Zhejiang University-SCIENCE A》 SCIE EI CAS 2010年第6期389-401,共13页
Turbulence in the wake generated by wind flow over buildings or obstacles may produce complex flow patterns in downstream areas.Examples include the recirculating flow and wind deficit areas behind an airport terminal... Turbulence in the wake generated by wind flow over buildings or obstacles may produce complex flow patterns in downstream areas.Examples include the recirculating flow and wind deficit areas behind an airport terminal building and their potential impacts on the aircraft landing on nearby runways.A computational fluid dynamics(CFD) simulation of the wind flow over an airport terminal building was performed in this study of the effect of the building wake on landing aircraft.Under normal meteorological conditions,the studied airport terminal building causes limited effects on landing aircraft because most of the aircraft have already landed before entering the turbulent wake region.By simulating the approach of a tropical cyclone,additional CFD sensitivity tests were performed to study the impacts of building wake under extreme meteorological conditions.It was found that,in a narrow range of prevalent wind directions with wind speeds larger than a certain threshold value,a substantial drop in wind speed(>3.6 m/s) along the glide path of aircraft was observed in the building wake.Our CFD results also showed that under the most critical situation,a drop in wind speed as large as 6.4 m/s occurred right at the touchdown point of landing aircraft on the runway,an effect which may have a significant impact on aircraft operations.This study indicated that a comprehensive analysis of the potential impacts of building wake on aircraft operations should be carried out for airport terminals and associated buildings in airfields to ensure safe aviation operation under all meteorological conditions and to facilitate implementation of precautionary measures. 展开更多
关键词 Aviation safety Building aerodynamics Computational fluid dynamics （CFD） k-e turbulence model Tropicalcyclone
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Numerical study on the ozone formation inside street canyons using a chemistry box model 认领 引用 被引量：2
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作者 Chun-Ho Liu Dennis Y.C.Leung 《Journal of Environmental Sciences》 SCIE EI CAS 2008年第7期832-837,共6页
Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NO_x),volatile organic compounds (VOCs),and solar radiation.In an urban environment,ground-level vehicular exhaust is the ma... Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NO_x),volatile organic compounds (VOCs),and solar radiation.In an urban environment,ground-level vehicular exhaust is the major anthropogenic source of ozone precursors.In the cases of street canyons,pollutant dilution is weakened by the surrounding buildings that creates localized high concentration of NO_x and VOCs,and thus leads to high potential of ozone formation.By considering the major physical and chemical p... 展开更多
关键词 volatile organic compounds VOCs-to-NO_x ratio air quality vehicular emission chemistry box model
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Uniform surface polished method of complex holes in abrasive flow machining 认领 引用 被引量：6
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作者 A-Cheng WANG Lung TSAI +2 位作者 Kuo-Zoo LIANG Chun-Ho LIU Shi-Hong WENG 《中国有色金属学会会刊：英文版》 2009年第B9期250-257,共8页
Abrasive flow machining(AFM)is an effective method that can remove the recasting layer produced by wire electrical discharge machining(WEDM).However,the surface roughness will not be easily uniform when a complex hole... Abrasive flow machining(AFM)is an effective method that can remove the recasting layer produced by wire electrical discharge machining(WEDM).However,the surface roughness will not be easily uniform when a complex hole is polished by this method.CFD numerical method is aided to design good passageways to find the smooth roughness on the complex hole in AFM.Through the present method,it reveals that the shear forces in the polishing process and the flow properties of the medium in AFM play the roles in controlling the roughness on the entire surface.A power law model was firstly set up by utilizing the effect of shear rates on the medium viscosities,and the coefficients of the power law would be found by solving the algebraic equation from the relations between the shear rates and viscosities.Then the velocities,strain rates and shear forces of the medium acting on the surface would be obtained in the constant pressure by CFD software.Finally,the optimal mold core put into the complex hole could be designed after these simulations.The results show that the shear forces and strain rates change sharply on the entire surface if no mold core is inserted into the complex hole,whereas they hardly make any difference when the core shape is similar to the complex hole.Three experimental types of mold core were used.The results demonstrate that the similar shape of the mold core inserted into the hole could find the uniform roughness on the surface. 展开更多
关键词 abrasive flow machining passageway uniform roughness
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Turbulent flows over real heterogeneous urban surfaces:Wind tunnel experiments and Reynolds-averaged Navier-Stokes simulations 认领 引用 被引量：2
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作者 Wai-Chi Cheng Chun-Ho Liu +6 位作者 Yat-Kiu Ho Ziwei Mo Zhangquan Wu Wenye Li Lilian Y.L.Chan W.K.Kwan Hing Tuen Yau 《Building Simulation》 SCIE EI CSCD 2021年第5期1345-1358,共14页
Wind tunnel experiment and steady-state Reynolds-averaged Navier-Stokes(RANS)approaches are used to examine the urban boundary layer(UBL)development above Kowloon Peninsula,Hong Kong Special Administrative Region(HKSA... Wind tunnel experiment and steady-state Reynolds-averaged Navier-Stokes(RANS)approaches are used to examine the urban boundary layer(UBL)development above Kowloon Peninsula,Hong Kong Special Administrative Region(HKSAR).The detailed urban morphology is resolved by computational fluid dynamics(CFD)and is fabricated by 3D-printing(reduced scale)for wind tunnel experiments.Different from the majority existing results based on idealized,homogeneous urban geometries,it was found that the wind and turbulence in the UBL over downtown Kowloon are characterized by the wake behind several high-rise buildings.In particular,local maxima of turbulence kinetic energy(TKE)and shear stress are found at the roof level of those high-rise buildings.In the downstream region where the flows are already adjusted to the urban surfaces,the urban roughness sublayer(URSL)can be further divided into two layers based on the structures of the mixing length/m,effective drag Dx and dispersive stress.In the lower URSL(z<100 m),lm is rather uniform,and the Reynolds stress and dispersive stress are comparable.In the upper URSL(100 m z s 300 m),on the contrary,lm is peaked at the mid-height and the magnitude of dispersive stress is smaller than that of the Reynolds stress(<30%).The effective drag Dx is negligible in the upper URSL. 展开更多
关键词 computational fluid dynamics(CFD) real urban morphology urban boundary layer(UBL) urban canopy model(UCM) wind tunnel experiments
Physio-chemical modeling of the NOx-O3 photochemical cycle and the air pollutants’ reactive dispersion around an isolated building 认领 引用 被引量：2
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作者 Yunfei Fu Xisheng Lin +5 位作者 Xing Zheng Liangzhu Wang Chun-Ho Liu Xuelin Zhang Cruz Y.Li K.T.Tse 《Building Simulation》 SCIE EI CSCD 2023年第9期1735-1758,共24页
A numerical physio-chemical model of the NOx-O3 photochemical cycle in the near-wake region of an isolated residential/office building has been presented in this study.The investigation delves into the dispersio... A numerical physio-chemical model of the NOx-O3 photochemical cycle in the near-wake region of an isolated residential/office building has been presented in this study.The investigation delves into the dispersion of reactive air pollutants through the lens of fluid phenomenology and its impact on chemical reactivity,formation,transport,deposition,and removal.Computational fluid dynamics(CFD)simulations were conducted for the ground-point-source(GES)and roof-pointsource(RES)scenarios.Results show that the Damköhler number(Da),which quantifies pollutants’physio-chemical timescales,displays a strong inverse proportionality with the magnitude and spread of NO–increasing Da reduces human exposure to the toxic NO and NO2 substantially.When different wind directions were considered,the dispersion range of NO exhibited varying shrinking directions as Da increased.Furthermore,as Da increases,the concentration ratio KNO2/KNOx,which quantifies the production of NO2 resulting from NO depletion,forms sharp high-low gradients near emission sources.For GES,the dispersion pattern is governed by the fluid’s phenomenological features.For RES,the intoxicated area emanates from the building’s leading-edge,with the lack of shielding inhibiting pollutant interactions in the near-wake,resulting in scant physio-chemical coupling.The NO2/NOx distribution follows a self-similar,stratified pattern,exhibiting consistent layering gradients and attributing to the natural deposition of the already-reacted pollutants rather than in-situ reactions.In the end,building design guidelines have been proposed to reduce pedestrian and resident exposure to NOx-O3. 展开更多
关键词 reactive pollutant dispersion NOx-O3cycle air pollution isolated building physio-chemical modelling
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