A MODEL EVALUATION PROTOCOL FOR URBAN SCALE FLOW AND DISPERSION MODELS

This paper reports on a comprehensive model evaluation protocol for urban scale flow and dispersion models that has been developed within the framework of the COST action 732 on Quality Assurance and Improvement of Micro-Scale Meteorological Models. It briefly discusses the different components forming model evaluation with particular emphasis on model validation and on the implementation of the protocol for a specific test case: the MUST (Mock Urban Setting Test) experiment. The protocol was first developed with building-resolving models in mind, but more traditional integral models have also been included. Currently the Action is finalising the MUST exercise results and will suggest the best approach for further model evaluation and for the standardization of CFD modelling practise for micro-scale meteorological applications

Modélisation de ladispersion etmosphérique en milieu complexe et incertitudes associées

MARNE-LA-VALLEE-ENPC-BIBL. (774682303) / SudocSudocFranceF

Modélisation micro-météorologique en milieu urbain (dispertion des polluants et prise en compte des effets radiatifs)

MARNE-LA-VALLEE-ENPC-BIBL. (774682303) / SudocSudocFranceF

A hybrid CFD RANS/Lagrangian approach to model atmospheric dispersion of pollutants in complex urban geometries

International audienc

BEST PRACTICE GUIDELINE FOR THE CFD SIMULATION OF FLOWS IN THE URBAN ENVIRONMENT: QUALITY ASSURANCE AND IMPROVEMENT OF MICROSCALE METEOROLOGICAL MODELS

The main objective of the COST Action 732 is the improvement and qualityassurance of micro-scale obstacle-accommodating meteorological models and theirapplication to the prediction of flow and transport processes in urban or industrialenvironments. This report contains the full best practice guidelines for undertaking simulations that areused to evaluate microscale obstacle-accommodating meteorological modelsSummaries of this report have been published as the following documents : Franke, J., Hellsten, A., Schlunzen, H. A., & Carissimo, B. (2010). The Best Practise Guideline for the CFD simulation of flows in the urban environment: an outcome of COST 732. In The Fifth International Symposium on Computational Wind Engineering (CWE2010) (pp. 1-10)Franke, J., Hellsten, A., Schlunzen, K. H., & Carissimo, B. (2011). The COST 732 Best Practice Guideline for CFD simulation of flows in the urban environment: a summary. International Journal of Environment and Pollution, 44(1-4), 419-427

A time-staggered CFD scheme for variable density moist air Flow

We present a conservative second order staggered time scheme for dry and moist variable density air flow implemented in the open source CFD solver code saturne. The staggered time arrangement introduced by Pierce and Moin [1] is extended to finite volumes and discontinuous solutions. An Helmholtz equation is solved in order include the thermodynamical pressure variation and to remove the acoustic CFL restriction. The internal energy equation supplemented by a corrective source term based on the kinetic energy dissipation [2] is solved, allowing the scheme to be consistent with discontinuous solutions. The water phase change is treated by considering thermodynamical equilibrium. Dalton’s law is used to compute the density and the temperature is obtained from the internal energy equation, solving with Newton’s method in case of phase change. A numerical analysis is presented to insure the positivity of the thermodynamic variables, followed by the scheme verification and validation. First, dry air cases are presented: a natural convection and shock cases are used to verify its accuracy related to singularities and buoyancy effects. Moreover, a pressure cooker like system shows the scheme good reproduction of pressure variations and correct time error convergences rates. Finally, the moist air module is verified against analytical cases

Micrometerological modeling of radiative and convective effects with a building resolving code

International audienc

3D Radiative and Convective Modeling of Urban Environment: An Example for the City Center of Toulouse

International audienc

Impact of trees on gas concentrations and condensables in a 2-D street canyon using CFD coupled to chemistry modeling

Trees grown in streets impact air quality by influencing ventilation (aerodynamic effects), pollutant deposition (dry deposition on vegetation surfaces), and atmospheric chemistry (emissions of biogenic volatile organic compounds, BVOCs). To qualitatively evaluate the impact of trees on pollutant concentrations and assist decision-making for the greening of cities, 2-D simulations on a street in greater Paris were performed using a computational fluid dynamics tool coupled to a gaseous chemistry module. Globally, the presence of trees has a negative effect on the traffic-emitted pollutant concentrations, such as NO2 and organic condensables, particularly on the leeward side of a street. When not under low wind conditions, the impact of BVOC emissions on the formation of most condensables within the street was low owing to the short characteristic time of dispersion compared with the atmospheric chemistry. However, autoxidation of BVOC quickly forms some extremely-low volatile organic compounds, potentially leading to the formation of ultra-fine particles. Planting trees in streets with traffic is only effective in mitigating the concentration of some oxidants such as ozone (O3), which has low levels in cities regardless of this, and hydroxyl radical (OH), which may slightly lower the rate of oxidation reactions and the formation of secondary species in the street