Flow in a Street Canyon for any External Wind Direction

Abstract

An analytical model has been developed for the flow along a street canyon (of height H and width W ), generated by an external wind blowing at any angle relative to the axis of the street. Initially, we consider the special case of a wind blowing parallel to the street. The interior of the street is decomposed into three regions, and the flow within each region is assumed to depend only on the external wind and the distance to the closest solid boundary. This decomposition leads to two different flow regimes: one for narrow streets (H/W > 1/2) and one for wide streets (H/W < 1/2). The theoretical model agrees well with results obtained from numerical simulations using a Reynolds-Averaged Navier-Stokes model. We then generalize the model to the case of arbitrary wind direction. Numerical solutions show that the streamlines of the mean flow in the street have a spiral form, and for most angles of incidence, the mass flux along the street scales on the component of the external wind resolved parallel to the street. We use this result to generalize the model derived for wind blowing parallel to the street, and the results from this model agree well with the numerical simulations. The model that has been developed can be evaluated rapidly using only very modest computing power, so it is suitable for use as an operational tool.

Multi-scale modeling of urban air pollution: development and application of a Street-in-Grid model (v1.0) by coupling MUNICH (v1.0) and Polair3D (v1.8.1)

“…These empirical wind profiles are exponential functions and are therefore qualitatively similar to the profile used in SIRANE (Soulhac et al, 2008) to derive the average wind velocity within the street canyon. The wind speeds calculated using these wind profiles and those in SIR-ANE are compared in Fig.…”

Influence of urban morphology on air flow over building arrays

“…Soulhac et al, 2008). However, no modifications to the flow immediately above the canopy are incorporated in this model.…”

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

“…As driven by ambient wind, street canyon flow is significantly influenced by external wind direction [9]. Soulhac et al [10] built a theoretical two-region street canyon model and revealed that the mean longitudinal velocity is proportional to Symmetry boundary condition was imposed at two side planes, while all other solid facets were set as no slip boundaries. A prescribed logarithmic profile [35] was adopted as the prevalent wind condition at the upstream inlet.…”

“…z is the aerodynamic roughness length, set as 0.03 m,  is von Karman's constant, set as 0. 41,10 U is the reference horizontal velocity at 10 m high, set as 1 m/s [36]. Symmetry boundary condition was imposed at two side planes, while all other solid facets were set as no slip boundaries.…”