Wind tunnel measurements for dispersion modelling of vehicle wakes

7 Wind tunnel measurements downwind of reduced scale car models have been made to study the 8 wake regions in detail, test the usefulness of existing vehicle wake models, and draw key 9 information needed for dispersion modelling in vehicle wakes. The experiments simulated a car 10 moving in still air. This is achieved by (i) the experimental characterisation of the flow, turbulence 11 and concentration fields in both the near and far wake regions, (ii) the preliminary assessment of 12 existing wake models using the experimental database, and (iii) the comparison of previous field 13 measurements in the wake of a real diesel car with the wind tunnel measurements. The experiments 14 highlighted very large gradients of velocities and concentrations existing, in particular, in the near– 15 wake. Of course, the measured fields are strongly dependent on the geometry of the modelled 16 vehicle and a generalisation for other vehicles may prove to be difficult. The methodology applied 17 in the present study, although improvable, could constitute a first step towards the development of 18 mathematical parameterisations. Experimental results were also compared with estimates from two 19 wake models. It was found that they can adequately describe the far–wake of a vehicle in terms of 20 velocities, but a better characterisation in terms of turbulence and pollutant dispersion is needed. 21 Parameterised models able to predict velocity and concentrations with fine enough details at the 22 near–wake scale do not exist. 23