Flow Dynamics Between Two Car Models: Influence Of The Intervehicle Distance

Abstract

Air pollution is a crucial issue since it is one of the major causes for worldwide deaths. Car drivers and passengers are daily exposed to high level of pollutant concentrations. The particles emitted from the tailpipe can disperse in the wake of the vehicle and then infiltrate the following car c abin. It has been demonstrated that the dynamics of such particles are highly affected by the properties of the flow downstream the emitting vehicle. In the present paper, the flow characterization in the wake of a simplified car model followed by a second vehicle is performed. Reduced-scaled Ahmed bodies are used. The upstream velocity is set to U∞ = 14.3 m/s, corresponding to a Reynolds number based on the simplified model’s height ( hc = 54 mm) of Re = 49500. Two leading vehicles with two different rear slant angles (φ = 0°, 25°) are considered. Two sets of experiments are carried out, one in the wind tunnel at ESTACA and the other in the wind tunnel at CORIA’lab. In the first measurement campaign, 2D LDV is used and six inter-vehicle distances ranging from d = 0.93 hc to 5.56 hc are considered and presented. The ITTT (Interarrival Time and Transit Time) method is applied to LDV data in order to ensure reliable results. Mean and turbulent properties of the wake between the two vehicles are described. The role of the rear slant angle is highlighted. A critical distance above which the followed vehicle has an insignificant influence on the flow topology downstream of the leading vehicle is identified. For further details, and taking into consideration the first results (from LDV measurements), Stereo-PIV measurements are used to get access to the three components of the velocity. Due to time constraint, only three inter-vehicle distances are discussed in this paper (0.93 hc, 1.85 hc and 3.70 hc). The SPIV results validate those obtained from LDV measurements and provide complementary information. The sensitivities of the bi-stability of the transverse velocity to the short inter-vehicle distance (0.93 hc) and to the slant rear angle are investigated. SPIV measurements are then correlated with LDA measurements taking into account this behavior. These measurements are completed by further measurements of concentrations of the exhausted particles from the tailpipe.