Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Computational Fluid Dynamics for urban physics: Importance, scales, possibilities, limitations and ten tips and tricks towards accurate and reliable simulations

50 years of Computational Wind Engineering: Past, present and future

Turbulent Schmidt numbers for CFD analysis with various types of flowfield

Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations – Evaluation of CFD data with experimental data

Recent progress in CFD modelling of wind field and pollutant transport in street canyons

A numerical study with a weather research and forecasting (WRF) model at 300-m resolution shows that Singapore’s canopy-layer UHI intensity has a strong diurnal cycle, peaking in early morning and keeping almost constant during late night and early morning. The modeled ensemble peak UHI intensity is 2.2 °C and it can reach 2.4 °C during early morning in the intensive industrial region in west Singapore. Numerical sensitivity tests are carried out to evaluate the mitigation effect of the cool roof and green vegetations at the city scale. The results reveal that the city-scale deployment of cool roofs can greatly reduce the near-surface air temperature and surface skin temperature during the daytime (especially at noon), but has little effect during nighttime. Green vegetation deployment, however, can reduce the near-surface air temperature by more than 1 °C during nighttime when the UHI intensity is high. This reduction can reach 2 °C at 02:00 LT in western Singapore. The detailed analysis shows that the higher latent heat flux and lower heat storage during daytime in green vegetation deployment are the key factors that contribute to the lower sensible heat flux, and hence lower near-surface air temperature. Moreover, the green vegetation will improve human’s physiological thermal comfort during early morning. It is therefore suggested that, under the specific meteorological conditions, the green vegetation is preferable in terms of mitigating the (nocturnal) UHI intensity in Singapore, albeit with some uncertainties and caveats to be considered in practice.

Evaluation of cool roof and vegetations in mitigating urban heat island in a tropical city, Singapore

Numerical investigation of pollutant transport characteristics inside deep urban street canyons

A large-eddy simulation (LES) with a one-equation subgrid-scale (SGS) model was developed to investigate the flow field and pollutant dispersion inside street canyons of high aspect ratio (AR). A 1/7th power-law wall model was implemented near rigid walls to mitigate the demanding near-wall resolution requirements in LES. This LES model had been extensively validated against experimental results for street canyons of AR = 1 and 2 before it was applied to the cases of AR = 3 and 5. A ground-level passive pollutant line source, located in the middle of the street, was used to simulate vehicular emissions. Three and five vertically aligned primary recirculations were developed in the street canyons of AR 3 and 5, respectively. The ground-level mean wind speed was less than 0.5% of the free stream value, which makes it difficult for the pollutant to be transported upward for removal. High pollutant concentration and variance were found near the buildings where the air flow is upwards. It was found that the velocity fluctuation, pollutant concentration and variance were all closely related to the interactions between the primary recirculations and/or the free surface layer. Several quantities, which are non-linear functions of AR, were introduced to quantify the air quality in street canyons of different configurations.

Xian-Xiang Li

Papers

Recent progress in CFD modelling of wind field and pollutant transport in street canyons

Evaluation of cool roof and vegetations in mitigating urban heat island in a tropical city, Singapore

Numerical investigation of pollutant transport characteristics inside deep urban street canyons

Large-Eddy Simulation of Flow and Pollutant Dispersion in High-Aspect-Ratio Urban Street Canyons with Wall Model

Development of a k–ε model for the determination of air exchange rates for street canyons