Abstract

Urban environments increasingly move to the fore of climate and air quality research due to their central role in the population’s health and well-being. Tools to model the local environmental conditions, urban morphology and interaction with the atmospheric boundary layer play an important role for sustainable urban planning and policy-making. uDALES is a high-resolution, building-resolving large-eddy simulation code for urban microclimate and air quality. uDALES solves a surface energy balance for each urban facet and models multi-refection shortwave radiation, longwave radiation, heat storage and conductance, as well as turbulent latent and sensible heat fluxes. Vegetated surfaces and their effect on outdoor temperatures and energy demand can be studied. Furthermore a scheme to simulate emissions and transport of aerosols and some reactive gas species is present. The energy balance has been tested against idealized cases and the particle dispersion against field measurements, yielding satisfying results. uDALES can be used to study the effect of specific new constructions and building measures on the local micro-climate; or to gain new insight about the general effect of urban morphology on local climate, ventilation and dispersion. uDALES is available online under GNU General Public License and remains under maintenance and development.

Highlights

  • With an ever-increasing number of people living in cities (UNFPA, 2012), understanding how the urban morphology influences 15 the transport of momentum, heat, moisture and pollutants is central to designing healthy, sustainable and safe urban environments

  • The large number of tall towers being erected in large cities around the world necessitate elaborate studies on how these affect the safety of pedestrians, since these structures channel high-momentum air down to ground level (Blocken et al, 2016)

  • 70 The aim of this paper is to present a new large-eddy simulation model for the urban environment, uDALES

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Summary

Introduction

With an ever-increasing number of people living in cities (UNFPA, 2012), understanding how the urban morphology influences 15 the transport of momentum, heat, moisture and pollutants is central to designing healthy, sustainable and safe urban environments. Wind engineering models are predominantly based on the Reynolds-averaged Navier-Stokes (RANS) equations, which require turbulence parameterisations for the full range of active scales in the flow field Blocken (2015). This allows for the use of relatively large time-steps, or even steady-state simulations that predict the flow field reasonably well. 70 The aim of this paper is to present a new large-eddy simulation model for the urban environment, uDALES This model is an extension of the atmospheric LES model DALES (Heus et al, 2010; Tomas et al, 2015).

Governing equations
Immersed boundary method
Top, bottom and immersed boundaries
Lateral
Wall-functions for momentum and temperature
Emissions and chemistry
Shortwave radiation budget
Surface energy budget of ground, wall and roof facets
Integration into LES
Validation using DAPPLE windtunnel experiments
Simulation set-up
Results
East Side demo
Full Text
Published version (Free)

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