Study on the wind field and pollutant dispersion in street canyons using a stable numerical method

Area of Science:

• Computational fluid dynamics
• Environmental engineering
• Urban meteorology

Background:

• Street canyons significantly influence wind flow and pollutant dispersion in urban environments.
• Accurate modeling of these phenomena is crucial for urban planning and air quality management.
• Previous models often made simplifying assumptions about rooftop flow patterns.

Purpose of the Study:

• To develop and validate a stable numerical model for simulating wind flow and pollutant dispersion in street canyons.
• To investigate the impact of building configurations and inflow velocity on flow dynamics.
• To provide insights into complex flow phenomena within street canyons.

Main Methods:

• A stable finite element method for time-dependent Navier-Stokes equations.
• A three-step fractional method for solving velocity and pressure fields.
• Streamline Upwind Petrov-Galerkin (SUPG) for numerical stability at high Reynolds numbers.

Main Results:

• The validated wind field model accurately predicted Strouhal numbers for flow over a square cylinder.
• Simulations revealed rooftop flow is not always parallel to the ground.
• A counter-clockwise vortex was observed with left-to-right inflow; increased building height enhanced pollutant dispersion.
• Flow regimes in street canyons remained consistent with increasing inflow velocity at high Reynolds numbers.

Conclusions:

• The developed finite element method provides a robust tool for analyzing urban wind flow and pollutant dispersion.
• The study challenges assumptions about rooftop flow and highlights the importance of building geometry.
• Findings offer valuable data for improving air quality models and urban design strategies.