Working Group CFD Modelling

of the TRAPOS network

It was decided during the TRAPOS midterm review meeting in Roskilde, January 2000, to create formal working groups for the different tasks of the network. Computational Fluid Dynamics (CFD) was defined as one of the tasks. The responsibilities of each working group are:

• Formulation of the importance of the subject for street level pollution
• Presentation of the TRAPOS contribution to the advancement of the subject
• Transformation of the results into recommendations for practical models

In order to understand the differences among the models, a table of detailed code-description and parameterisation (Table_codes.doc) was constructed.

A general description including references for most ot the codes can be found in the Model Inventory build in the frame of a European COST project.

Goals

1. to assess and allocate the source of differences that appear when different CFD codes using the same turbulence model are applied to well defined test cases and
2. to improve the knowledge base for model development and application
3. to demonstrate the level of agreement that can be expected from CFD modelling in urban environment
4. to give guidance for the procedure of the case set-up e.g. grid and inflow definitions, boudary conditions etc.
5. to prove the CFD codes to be a powerful reliable tool for application in practical situation and for improvement of practical street pollution models.

• One of the objectives of our future activities is to define all conditions for the model-runs precisely enough so that principally similar CFD codes show reasonable agreement in their results.
• We finished two rounds of model runs for the most test cases. After the processing of all the available model results we had two group meetings to discuss the results.
• The results obtained show in some cases discrepancies that are not acceptable, as the models are in principle similar. Therefore, there is need to find explanations. We concluded that these discrepancies are due to the differences in the boundary conditions as well as due to the different values of constants etc. that each model uses.
• We are in the process of publication of our results at conferences, in journals and in this web page.

P.Louka, P.Sahm, M.Ketzel, G.Theodoridis, J.-F.Sini & N.Moussiopoulos: An intercomparison of microscale models for the flow and dispersion characteristics in urban areas. Poster presented at the EUROTRAC-2-symposium, 27-31 March 2000, Garmisch-Partenkirchen, Germany. (The poster can be downloaded as MS-Publisher document as well as the exteded abstract as MS-Word file)

P. Sahm, P. Louka, M. Ketzel, E. Guilloteau, J-F. Sini: Intercomparison of numerical urban dispersion models - Part I: street canyon and single building configurations. Abstract submitted for presentation at The Third International Conference on Urban Air Quality, Loutraki, Greece, 19-23 March 2001.

M. Ketzel, P. Louka, P. Sahm, E. Guilloteau, J.-F. Sini, N. Moussiopoulos: Intercomparison of numerical urban dispersion models - Part II: street canyon in Hannover, Germany. Abstract submitted for presentation at The Third International Conference on Urban Air Quality, Loutraki, Greece, 19-23 March 2001.

P. Louka, M. Ketzel, P. Sahm, E. Guilloteau, N. Moussiopoulos, J.-F. Sini, P.G. Mestayer, R. Berkowicz: CFD Intercomparison Exercise within TRAPOS European Research Network. Abstract submitted for presentation at 7th Conference on Environmental Science & Technology, Syros, Greece, 3-6 September 2001.

M. Ketzel, P. Louka, P. Sahm, E. Guilloteau, J.-F. Sini: The use of computational fluid dynamics in modelling air quality in street canyons. Chapter 2.2 of the TRAPOS summary report in preparation.