Sensitivity Analysis of Coastdown Test Cycle Averaged Drag Coefficient for Several Functions of Drag Coefficient vs. Speed 2020-01-0663
Aerodynamic testing for predicting fuel economy effects is typically done at EPA nominal ambient conditions, with nominal ‘2 Pass’ vehicle attitude. Essentially, the EPA standard coastdown is simulated in the wind tunnel. This predictive model is typically used well in advance of production manufactured vehicles, when prototype models are used for wind tunnel testing.
However, in reality the actual loading of the vehicle due to manufacturing tolerances, changes in ride height with test loading, and the change in drag coefficient CD with speed, results in some variation in the vehicle CD during a coast down test. By testing the prototype vehicle on track with ride height sensors and at several ride height variations in the wind tunnel, a mathematical model can be used to predict the coast down speed effects on aerodynamic drag.
Gregory Fadler, Todd Lounsberry, John Tripp