Extending a RANS Solver with heat and pollution modules for dispersion problems in urban areas with vegetation

Abstract

Currently, 54% of the general population lives in urban areas. This number is estimated to increase to 66% by 2050. Urbanization is generally linked to several phenomena that are detrimental to the overall quality of life; the urban heat island effect, and the decrease of air quality due to pollutants. The addition of vegetation to urban areas is generally seen as the best measure to combat these phenomena, due to their suggested filtering and cooling capacity. Currently, both phenomena are studied as separate processes, but research suggest that the cooling power of vegetation is linked to the amount of pollution that is present. This calls for a numerical implementation that is able to accurately model both the filtering, and cooling effect such that the interplay between them can be studied in the future. In this work, an existing RANS k− solver is extended with the dry-deposition model to deter-mine the filtering capacity of the vegetation, and the leaf energy balance model to determine the cooling effect of the vegetation. Using the dry deposition model, we were able to accurately reproduce experimental measurements of the filtering capacity of a hawthorn hedge in an open field, obtained by Tiwary et al. [2006]. We assumed that the filtering took place due to both needle-like and broad leaf collectors. The same case was studied byˇS ́ıp and Beneˇs [2016], who obtained similar results, but used a different mixing parameters of the collector types. We concluded that additional studies are needed to determine the importance of the collector mixing parameters for multiple species, before the dry deposition model can be considered as valid. Using the leaf energy balance model, we were able to determine the cooling power of a simple vegetation block, exactly reproducing the results obtained by [Manickathan et al., 2017]. Using the leaf energy balance model, we were not able to reproduce experimental measurements of the leaf temperature of potted impatiens, obtained by [Kichah et al., 2012]. This was caused by the nature of the flow, which proved to be barely turbulent and outside of the scope of our RANSk− solver. We concluded that the leaf energy balance model needs to tested against other experimental measurements, obtained under different flow conditions. As of yet, we cannot determine if the model is able to accurately reproduce experimental measurements.