Wake Traverses Behind Production Cars and Their Interpretation

Over the past decades substantial advances have been made in reducing the drag of automobiles. As might have been expected, the early performance gains were relatively easy but future gains are becoming increasingly difficult to achieve. A diagnostic method which is both quantitative and independent of the model is sorely needed. This paper discusses experimental measurements of wakes behind. 154-scale model production cars and comparisons to balance measurements. Models, test equipment, and data analysis are discussed. Explanations of the wake flow results in relation to the car modifications are included. Correlation of the wake drag integral to the balance drag measurement is good; however, some questions remain relative to the influence of fixed-ground skin friction.