Simulations of dispersion through an irregular urban building array

Area of Science:

• Environmental Science
• Atmospheric Science
• Computational Fluid Dynamics

Background:

• Urban environments present complex flow regimes affecting pollutant dispersion.
• Existing fast-response dispersion models require refinement for urban complexities like plume channeling and spreading.
• Accurate modeling of releases in nonhomogeneous urban structures is crucial for public safety.

Purpose of the Study:

• To examine tracer concentrations and plume behavior in a mock urban setting.
• To compare wind tunnel experiments with Embedded Large Eddy Simulation (ELES) for microscale dispersion effects.
• To evaluate the applicability and limitations of Gaussian plume models, like AERMOD, in urban areas.

Main Methods:

• Conducted wind tunnel experiments using a full-scale mock urban building configuration.
• Employed Embedded Large Eddy Simulation (ELES) to model tracer dispersion.
• Utilized AERMOD to assess fast-running Gaussian dispersion model performance in urban scenarios.

Main Results:

• Wind tunnel and ELES showed excellent agreement in representing plume concentration profiles.
• Initial plume dispersion was heavily influenced by adjacent structures, leading to rapid near-surface spread.
• ELES revealed significant off-axis plume channeling (5-14°) at ground level with oblique wind directions.
• AERMOD qualitatively represented ground-level plumes but underestimated peak concentrations and struggled in the near-field.
• Incorporating ELES turbulence data into AERMOD improved lateral spread and centerline concentration estimates.

Conclusions:

• Gaussian plume models can represent urban concentration profiles but require careful parameterization.
• Building structures significantly alter plume behavior, causing channeling and drift, especially with oblique winds.
• ELES provides valuable data for improving the accuracy of urban dispersion models.