Computational Fluid Dynamics Modelling of the Diurnal Variation of Flow in a Street Canyon

Abstract

Urban surface and radiation processes are incorporated into a computational fluid dynamics (CFD) model to investigate the diurnal variation of flow in a street canyon with an aspect ratio of 1. The developed CFD model predicts surface and substrate temperatures of the roof, walls, and road. One-day simulations are performed with various ambient wind speeds of 2, 3, 4, 5, and 6 ms −1 , with the ambient wind perpendicular to the north-south oriented canyon. During the day, the largest maximum surface temperature for all surfaces is found at the road surface for an ambient wind speed of 3 m s −1 (56.0 • C). Two flow regimes are identified by the vortex configuration in the street canyon. Flow regime I is characterized by a primary vortex. Flow regime II is characterized by two counter-rotating vortices, which appears in the presence of strong downwind building-wall heating. Air temperature is relatively low near the downwind building wall in flow regime I and inside the upper vortex in flow regime II. In flow regime II, the upper vortex expands with increasing ambient wind speed, thus enlarging the extent of cool air within the canyon. The canyon wind speed in flow regime II is proportional to the ambient wind speed, but that in flow regime I is not. For weak ambient winds, the dependency of surface sensible heat flux on the ambient wind speed is found to play an essential role in determining the relationship between canyon wind speed and ambient wind speed.

Seasonal Changing Effect on Airflow and Pollutant Dispersion Characteristics in Urban Street Canyons

“…In this section, the along-canyon averaged streamline fields [52] were calculated. Figure 8 details the wind-buoyancy-driven flow behavior within the street canyon under different seasonal conditions.…”

A numerical study of diurnally varying surface temperature on flow patterns and pollutant dispersion in street canyons

“…According to the study conducted by Kwak et al (2011), reasonable temperature boundary conditions representing four typical time events (morning, noon, afternoon, and night) are predefined to represent a reasonable temperature diurnal variation (Table 1). All building roofs are assumed to be adiabatic and the thermal stratification of the inflow is set as neutral.…”

Development of a Building-Scale Meteorological Prediction System Including a Realistic Surface Heating

“…Microscale meteorological models have been widely used in investigating atmospheric flow, dispersion, and thermal comfort conditions in urban environments, compensating for the limitations in the wind tunnel experiments and field measurements (e.g., [9][10][11][12][13][14][15][16][17]). Kim and Baik [9] found that urban morphology is an important factor in determining in-canyon flow and turbulence in an ideal two-dimensional canyon morphology using a computational fluid dynamics (CFD) model.…”