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Air Quality Part 10

Tham khảo tài liệu 'air quality part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 218 Air Quality only one vortex appears at the right edge of the upwind building as the incoming wind enters from that side. As the angle 0 increases the vortex size decreases and the flow towards the domain exit in the y-direction increases. This pattern shows an improvement in the domain wind removal efficiency compared with the case of normal wind. y x Fig. 11. Horizontal wind vector fields at different wind directions z 0.05 m . The third pattern appears when the wind flows with an angle of 90o. The vortex in that case diminishes and the wind flows smoothly towards the domain exit which indicates that the removal efficiency of the domain local wind in that that pattern is the best over the above two patterns. Results of the numerical approach for the pollutant concentration inside the street canyon are displayed in Fig. 12. The figure shows the concentration fields at z 0.05 m for the five wind directions. In the case of normal wind the concentration field shows symmetry around the central section of the street. It is observed that high concentration regions appear inside the street canyon while very low concentration regions appear outside it. That note means that the domain local wind has no ability to carry the pollutants outside the canyon. Modeling of Ventilation Efficiency 219 kg kg 0.0018 0.0016 0.0015 0.0014 0.0013 0.0011 0.0010 0.0009 0.0008 0.0006 0.0005 0.0004 0.0002 0.0001 0.0000 Fig. 12. Concentration fields for different wind directions z 0.05 m . y __ x In the cases 0 30o 45o and 60o the concentration field increased to cover a wide area outside the study domain due to pollutant diffusion towards the outside in the same wind direction. As the maximum concentration area decreases with increasing 0 the canyon averaged concentrations are expected to be lower than the concentration of the case of normal wind as clean air continuously comes into the canyon from outside and dilutes the domain polluted air. Also it is observed that very low .