EXPERIMENTAL STUDY OF THE INTERACTION BETWEEN TWO VEHICLES: THE EFFECT OF THE INTER-VEHICLE DISTANCE ON THE RECIRCULATION ZONE

Air quality is a key issue worldwide. Cars are a significant contributor to pollutant emissions. Ultrafine particles emitted from the tailpipe disperse in the wake of the vehicle. They can infiltrate the following vehicle exposing drivers and passengers to potential high concentrations of pollutants. Once released in the atmosphere, the particle dynamics is strongly affected by the flow topology in the near wake of the emitting vehicle, the recirculation region playing a key role. This has been demonstrated for a single vehicle. The present paper aims at extending this result to the interaction between two vehicles with different inter-vehicle distances. An experimental study was undertaken in the wind tunnel at ESTACA. Velocity measurements were conducted using a 2D LDV system. Reduced-scaled Ahmed bodies were used, the leading one having different rear slant angles (phi=0 degrees, 25 degrees, 35 degrees). The inter-vehicle distance ranges from d=0.93h (h being the height of the vehicle) to d=5.56h. Mean and turbulent flow properties between vehicles were described. A detailed discussion is proposed regarding the effect of the rear slant angle of the leading vehicle on the wake flow. We show that d influences the size of the recirculation zone, which volume strongly influences particle dispersion. We identify a critical distance above which the leading vehicle has no more influence on the following one. In terms of application, this study can lead to a better understanding of how pollutants emanating from the tailpipe can disperse and infiltrate a following vehicle in real traffic conditions.