The Influence of Roughness Elements on Laminar to Turbulent Boundary Layer Transition as Applied to Scale Model Testing of Automobiles

When undertaking investigations into the aerodynamic behavior of automobiles using scale models in a wind tunnel, Reynolds number dynamic equivalence is often difficult or impossible to obtain. The boundary layer transition from laminar to turbulent flow thus does not occur at a point on the model which corresponds to the transitional location on the real vehicle. To improve results obtained in such tests, roughness elements can be applied to the scale model to be tested and the transitional position of the boundary layer manipulated to correspond to the position of transition on the actual vehicle of interest. This paper describes such techniques and illustrates their use.