On the Predicted Effectiveness of Climate Change Adaptation Measures for Outdoor Thermal Comfort using CFD /
Muhammad Zeeshan
- 145p. Soft Copy 30cm.
The urban heat island (UHI) phenomenon has become a major concern for urban sustainability in the wake of global warming and rapid urbanization. This has resulted in increased heat stress and worsened outdoor thermal comfort in urban microclimates. Vegetation, water bodies, and cool materials are one of the most effective strategies to alleviate the adverse effects of rising outdoor temperatures. Computational fluid dynamics (CFD) has established itself as a valuable tool to model various urban physics phenomena and develop climate change and UHI mitigation and adaptation strategies. However, there exist certain numerical modeling aspects which require further insight. In this work, CFD simulations have been performed to analyze the effect of more realistic vegetation modeling parameters. The vegetation modeling parameters include the actual form drag coefficient and the variable tree transpiration rate. In addition to that, thermal comfort effectiveness of different tree species with its various morphological characteristics, cool materials’ albedo, and water bodies have also been studied in individual and in combination for a real urban area. The morphological characteristics/parameters include trunk height (HT), crown diameter (CW), crown height (CH), and leaf area density (LAD). The wind flow and heat transfer phenomena are simulated using the unsteady Reynolds-averaged Navier– Stokes (URANS) approach. The simulations were performed with proposed adaptation measures for a real urban area having hot-humid climatic conditions under heat wave conditions. It has been found that for the studied climatic conditions, the consideration of more realistic values of these parameters can yield significant variation in the determination of cooling potential and flow characteristics of applied vegetation. Of all the morphological characteristics, LAD, crown height, and trunk height are found to be most influential in providing thermal comfort. Water bodies promotes improved thermal conditions and urban ventilation in spatial direction. Water and vegetation interventions promote the cooling effect by resulting in low ambient air and surface temperature i.e. 0.9 °C and 3.5 °C; 0.3 °C and 3 °C respectively when compared with reference case. Cool materials, when applied simultaneously on both buildings and ground, generate a more pronounced cooling effect than when applied separately on ground or the buildings as it results in a large reduction of air and surface temperature i.e., of 2 °C and 6 °C respectively. Furthermore, the impact becomes more significant for collective application of these adaptation measures. Cool materials when combined with vegetation and water results in large reduction i.e. 2.2 °C and 1.9 °C in air temperature; and 5.9 °C and 9 °C in surface temperature was observed respectively compared to the reference case. For air flow velocity, it is highest for combined cool materials with water with peak effect at the time of highest solar irradiance. The analysis shows that the proposed interventions can effectively decrease surrounding temperature and promote airflow; thereby promoting thermal comfort conditions.