FLOW FIELD AROUND AND IN A SAAB 9-3 CONVERTIBLE

Paper in proceeding, 2009

The aerodynamic comfort in a four seated convertible with open roof is not as good as many would like it to be. This job was initiated to look at what should be done to improve this. The car used for this study was a Saab 9-3 convertible. Most of the work was done in CFD in the commercial code Fluent. The flow field in the cockpit was first of all analyzed and evaluated. The problem with convertibles is the large recirculation bubble that occurs around the passenger compartment. The rear seat passengers are located in an area of this zone with very high wind speeds compared to the front seat passengers. The flow field was analyzed by several pressure and velocity plots and a method to evaluate comfort grading was developed. The selected main variable to compare cases was the mean velocity that the passengers head is exposed to. This was found to be the most affecting parameter because it affects not only the dynamic pressure, but also the temperature discomfort. Geometry optimizations of windows, wind shield and wind blockers have been simulated and evaluated. Height and length of the side windows and a number of different wind deflectors on the wind shield, plus wind blockers inside and behind cockpit was tested. The results show that the biggest potential of improvement is the wind deflector on the windshield and some of the wind blockers.