Aerodynamic Investigation of Cooling Drag of a Production Pickup Truck Part 1: Test Results 2018-01-0740
The airflow that enters the front grille of a ground vehicle for the purpose of component cooling has a significant effect on aerodynamic drag. This drag component is commonly referred to as cooling drag, which denotes the difference in drag measured between open grille and closed grille conditions. When the front grille is closed, the airflow that would have entered the front grille is redirected around the body. This airflow is commonly referred to as cooling interference airflow. Consequently, cooling interference airflow can lead to differences in vehicle component drag, this component of cooling drag is known as cooling interference drag. One mechanism that has been commonly utilized to directly influence the cooling drag, by reducing the engine airflow, is Active Grille Shutters (AGS). For certain driving conditions the AGS system can restrict airflow from passing through the heat exchangers, which significantly reduces cooling drag. The difference in drag between the AGS vanes being open and closed is referred to as AGS drag. Another vehicle component that influences the cooling drag are chin spoilers. Chin spoilers are components that lie within cooling interference airflow paths for many vehicles and can be used/designed to affect cooling drag. This study focuses on the influence of the chin spoiler on cooling and AGS drag of a production level F-150 in a wind tunnel test environment. The chin spoiler variables tested were height and curvature (sweep). All experiments were conducted in both stationary and moving ground wind tunnel conditions at 80 MPH between yaw angles of +/−7°. In addition to overall vehicle drag coefficients, surface pressures at discrete locations and cooling pack airflow rates were measured to provide better insight into the internal and external airflow behaviour. Ground and yaw conditions were shown to heavily influence chin spoiler design. Cooling and AGS drag were also strongly influenced by chin spoiler height at 0° yaw, at higher angles of yaw this influence was lessened but was still present. Chin spoiler sweep was shown to have a significantly lesser (though non-negligible) impact than chin spoiler height on all metrics in all conditions.