25 2 2012 2 Research of Environmental Sciences Vol 25 No 2 Feb 2012 J 2012 25 2 159-164 ZHANG Chuanfu ZENG Jianrong WEN Mou et al Influence of viaducts on dispersion of air particles in street canyons J Research of Environmental Sciences 2012 25 2 159-164 1 1 2 1 1 1* 1 201800 2 200072 CFD 3 H W k-ε H W CFD X513 A 1001-6929 2012 02-0159 - 06 Influence of Viaducts on Dispersion of Air Particles in Street Canyons ZHANG Chuan-fu 1 ZENG Jian-rong 1 WEN Mou 2 ZHANG Gui-lin 1 FANG Hai-ping 1 LI Yan 1 1 Key Laboratory of Nuclear Analysis Techniques Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai 201800 China 2 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai 200072 China Abstract Due to the increase of private vehicles in cities in China high-level pollution is often detected in urban street canyons Using a two-dimensional computational fluid dynamics CFD model the environmental impacts of viaducts on the wind flow and dispersion of particles were studied under three different height width ratios H W of street canyons Two-dimensional flow and dispersion of particles from traffic exhaust were modeled using the standard k-ε turbulence and discrete phase models The results revealed that increasing the H W effectively raised the particle concentration and mean particle residence time The airflows were obviously disturbed at the region around the viaduct whereas there was no significant change of the airflows near the walls of the buildings the ground and the roofs of the canyon The particle concentration at the lower part of the walls increases when a viaduct exists in the street canyons Key words street canyons viaduct particle dispersion CFD 1-4 ρ PM 10 ρ PM 2 5 ρ PM 10 10 μg m 3 2011-04 - 26 2011-06 - 28 KJCX3 - SYW - N3 11079049 11005141 1983 - zcf0225@ 126 com * 0 51% 0 68% 1964 - ly@ sinap ac cn 7-8 ρ PM 2 5 10 μg m 3 4% 3% 2% 5-6 PM 0 1 0 1 μm
160 25 ε + U ε 9-10 j = ν t x CFD 3 20 a t x j x j x j CFD ε U i C k ε1 ν t + U U j i - C x j x x ε2 ε 2 i j XIE 11 k-ε x i y i i j U i U j RNG k-ε i j i j = 1 2 t k ε ν 12 AHMADI 13 t = C μ k 2 ε C μ = 0 09 C ε1 = 1 44 C ε2 = 1 92 σ 14 k = 1 0 σ ε = 1 3 1 2 KUMAR 15-16 5 ~ 1 000 nm nm CFD du 17 18 p = F dt D u - u p + g ρ p - ρ + F a 3 ρ 19 p u p u ρ p ρ F D g F 20-22 a u = u 珔 + u' u珔 k-ε 53 2 km u' 23 0 15 24 Fluent 1 CO F KONDO 25 drag Stokes NO x 18μ F drag = F D u - u p = u - u ρ p d 2 p 4 p C c CFD d p μ C c Stokes Cunningham 3 1 dx dt = u p 5 1 1 N Navier-Stokes N = k-ε k-ε Σ n i dt i i n i i dt i k t + k U j = x j x j ν t k ( σ k x ) j U ( ) i U i + ν t + U j x j xi x j - ε 1 ( ) σ ε [ ( ) ] 2 1 +
2 161 1 Fig 1 Schematic diagram of street canyon with a viaduct 3 m s H W H W 0 5 3 H W 0 5 1 2 W 20 m H W 1 2 w 12 m h 5 m = 0 01W x min y min = 0 01H 10 000 3 3 1 2 3 2 Fig 2 The wind stream lines in a street canyon 3 2 m 60% x ± 1 ± 3 ± 5 m y 0 3 ~ 1 1
162 25 K = CU H HL Q Q 6 K C A K B U H H L Q Q A K 27 3 A H W 0 5 K B K A K 3 K 2 5 μm K H W 2 28-29 A K H W 0 5 2 3 C c 0 01 ~ 10 μm 4 10 μm 300 nm 1% 28 30 4 K 0 1 μm Fig 4 Distributions of particles numbers at wall in street canyons μm 1 0 01 2 0 1 3 2 5 4 10 3 H W 0 5 K A Fig 3 Distributions of particles numbers with different size at wall A in street canyon with H W = 0 5 K GROMKE 5 A H W 0 5 A K H W 1 2 A K A 31 5 4 A A B Fig 5 Influence of a viaduct on the distribution 4 K particles numbers at wall A
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