Aerodynamic Investigation of Cooling Drag of a Production Sedan Part 1: Test Results

The airflow that enters the front grille of a ground vehicle for the purpose of component cooling has a significant effect on aerodynamic drag (engine airflow drag). Furthermore, engine airflow is known to be capable of influencing upstream external airflow (interference drag). The combined effect of these phenomena is commonly referred to as cooling drag, which generally contributes up to 10% of total vehicle drag. Due to this coupled nature, cooling drag is difficult to understand as it contains influences from multiple locations around the vehicle. A good understanding of the sources of cooling drag is paramount to drive vehicle design to a low cooling drag configuration. In this work, a production level Lincoln MKZ was modified so that a number of variables could be tested in both static ground and moving ground wind tunnel conditions. All tests were conducted at 80 MPH. The variables studied were: underbody shield coverage, heat exchanger resistance, cooling pack configuration, vehicle attitude, front-end sealing, exit path sealing, engine bay blockage and active grille shutter (AGS) configuration. In addition to overall vehicle drag coefficients, surface pressure taps, underbody velocity rakes and cooling pack mass flows were measured to provide better insight into the internal and external flow behaviour. This paper represents the first of a two-part series, with experimental and numerical foci respectively.