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This dissertation, Effect of Heat Flux on Wind Flow and Pollutant Dispersion in an Urban Street Canyon by Ching, Cheung, 張靜, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Effect of Heat Flux on Wind Flow and Pollutant Dispersion in an Urban Street Canyon Submitted by Cheung, Ching for the degree of Master of Philosophy at The University of Hong Kong in August 2006 The effect of heat flux on wind flow and pollutant dispersion in an urban street canyon is investigated in this study. A constant temperature difference is applied to windward wall, leeward wall, canyon ground, both walls and ground to model four heating configurations from solar irradiation or urban heat emission. For each heating configuration, the Reynolds number is varied from 400 to 3000 to model different inflow speed, and the Grashof number is raised from 0 to 800000 to model increasing heating strength. Canyon aspect ratio and building height ratio range from 0.3 to 2.0 are configured to study the heating effect in different canyon geometries. A retention value is used to compare the efficiency of canyon pollutant dilution under each respective heating and canyon configuration. Computational method based on large eddy simulation (LES) is applied to carry out the analysis. Governing equations used are the continuity equation, momentum equations with Boussinesq's approximation, energy equation, and scalar transport equation. The equations are filtered using box filter for large eddy simulation. The filter process decomposes every field variable into filtered quantity plus residue quantity. The filtered quantities are resolved directly and the residue quantities are modelled by static Smagorinsky's subgrid scale model to obtain the closure. The equations for LES are discretised in both space and time domains through finite difference method. Continuity constraint is surmounted by using artificial compressibility method while requirement of pressure boundary conditions is avoided by use of marker and cell mesh in space discretisation. Poisson pressure equation is used to allow explicit pressure calculation. Numerical results show heating can significantly change the flow and hence pollutant dispersion inside canyon. When windward wall is heated, the main vortex in the canyon is weakened and the windward corner vortex is strengthened. The windward corner vortex grows with increasing heating strength and eventually merges with the leeward corner vortex. The merged vortex is further strengthened by stronger heating. When leeward wall is heated, the main vortex is strengthened and the leeward corner vortex is weakened. If ground is heated or both walls and ground are heated, the temperature distribution in the canyon can be even if the inflow speed is low, or skewed towards the windward wall if the inflow speed is high enough. The evenly distributed temperature results in no strengthening or weakening of vortices. The skewed temperature distribution behaves like windward heating. The observed effect for all heating configurations, however, diminishes with increasing inflow speed and varies with canyon geometry. Pollutant dispersion, which is heavily dependent on the flow behavior, is also affected by heating configuration and heating strength. It is evident that the effect of heating, depending on where it is applied and how strong it is, can significantly change the behavior of flow and hence pollutant dispersion in street canyons. The heating effect, which can be different when canyon geometry or inflow property is changed, should

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