Influence of wall roughness on the dispersion of a passive scalar in a turbulent boundary layer |
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| Authors: | P Salizzoni R Van Liefferinge L Soulhac P Mejean RJ Perkins |
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| Institution: | 1. Laboratoire de Mécanique des Fluides et d''Acoustique, Université de Lyon CNRS, École centrale de Lyon, INSA Lyon, Université Claude Bernard Lyon I, 36, avenue Guy de Collongue, 69134 Ecully, France;2. Dipartimento di Ingegneria Aerospaziale, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, Italy;1. Il''ichev Pacific Oceanological Institute, 43 Baltiyskaya str., Vladivostok, 690041, Russia;2. Far Eastern Federal University, 8 Sukhanova str., 690950, Vladivostok, Russia;1. Centre de Mathématiques et de Leurs Applications, Ecole Normale Supérieure de Cachan and CNRS UMR8536, 61, Avenue du Président Wilson, 94235 Cachan Cedex, France;2. School of Mathematical Sciences, University College Dublin, Belfield, Dublin 4, Ireland;3. Laboratoire de Mathématiques d’Orsay and CNRS UMR8628, Université Paris-Sud XI, Bât. 425, 91405 Orsay Cedex, France;4. Commissariat à l’Énergie Atomique et aux Énergies Alternatives, Centre de Bruyères-le-Châtel, 91297 Arpajon Cedex, France;1. Laboratoire de Mécanique des Fluides et d’Acoustique, UMR CNRS 5509 University of Lyon, Ecole Centrale de Lyon, INSA Lyon, Université Claude Bernard Lyon I, 36, avenue Guy de Collongue, 69134 Ecully, France;2. Compagnie Nationale du Rhône, Engineering Department, River Systems and Climate Hazards Division, 2, rue André Bonin, 69004 Lyon, France;3. Air Rhône-Alpes, 3 allée des Sorbiers, 69500 Bron, France;4. CEA, DAM, DIF, F-91297 Arpajon, France |
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| Abstract: | Many towns and cities consist of similarly sized buildings in relatively regular arrangements with smaller scale roughness elements such as roofs, chimneys and balconies. The objective of this study is to investigate how small scale roughness elements modify the influence of the large scale organized roughness on the dispersion of a passive scalar in a turbulent boundary layer. Wind tunnel experiments were performed using a passive tracer released from a line source and concentration profiles were measured with a Flame Ionisation Detector. The measurements are compared with numerical solutions of the advection–diffusion equation.The results show that decreasing the cavity aspect ratio increases the turbulent vertical mass fluxes, and that the small scale roughness enhances these fluxes, but only in the skimming flow regime. Numerical simulations showed that outside the roughness sub-layer (RSL) the changes in surface roughness could be accounted for by a simple variation of the friction velocity, but inside the RSL the spatial variability of the flow imposed by the roughness elements has much more influence. A simple model for a spatially averaged dispersion coefficient in the RSL has been developed and is shown to agree satisfactorily with the concentrations measured in these experiments. |
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