Effects of an air spoiler on the wake of a road vehicle by PIV measurements

Abstract

A particle image velocimetry (PIV) technique has been used to analyze the flow characteristics behind a road vehicle with/without an air spoiler attached on its trunk and also to estimate its effect on the wake. A vehicle model scaled in the ratio of 1/43 is set up in the mid-section of a closed-loop water tunnel. The Reynolds number based on the vehicle length is 10 5 . To investigate the three-dimensional structure of the recirculation zone and vortices, measurements are carried out on the planes both parallel and perpendicular to the free stream, respectively. The results show significantly different vorticity distributions in the recirculation region according to the existence of the air spoiler. The focus and the saddle point, appearing in the wake, are disposed differently along the spanwise direction. Regarding the streamwise vortices, the air spoiler produces large wing tip vortices. They have opposite rotational directions to C-pillar vortices which are commonly observed in the case that an air spoiler is absent. The wing tip vortices generate the down force and as a result, they might make the vehicle more stable in driving.

PIV measurements on the change of the three-dimensional wake structures by an air spoiler of a road vehicle

“…However, these studies did not completely verify the whole wake phenomena including recirculation, but simply investigated the flow features. Recently, we reported on the PIV measurements in the wake of a downscaled sports car model at several sections and discussed the structural changes of the three-dimensional vortices caused by an air spoiler (Kim, et al, 2006), but we did not show the full three-dimensional vortical structure because of the lack of information on the out-of-plane velocity component. Meanwhile, many strategies were tried to find out three-dimensional vortical structures for simple geometric flows.…”

“…On the other hand, with an air spoiler, they are remarkably weakened and nearly disappear because of strong streamwise wing tip vortices with opposite rotational direction, as shown in the figure of Fig. 8(b) (Kim et al, 2006). …”

“…The vorticity contours in Fig. 7 result from two-dimensional data obtained in our previous work (Kim et al, 2006) and λ2 contours in Fig. 8 show the sectional views of the three-dimensional data.…”

“…Finally, the velocity vector retained the spatial resolution of 1.3, 1.1 and 1.1 vector/mm for the x-y, y-z and z-x planes, respectively. See our previous work (Kim et al, 2006) for more details about the experimental system.…”

Experimental investigation of spoiler application in an SUV type vehicle

“…Especially the application of a spoiler or wing to the rear of the vehicle are the most preferred flow control elements. Here, the shape, structure and position of the spoiler and wing significantly affect the flow [5][6][7][8]. Rear spoilers can be defined as aerodynamic devices that are usually added to the trailing edge of the roof or trunk deck of a vehicle to improve its aerodynamic performance.…”