External Aerodynamic Drag Coefficient Prediction of Full Scale Passenger Car Based on Scale Model Assessment

Aerodynamics performance evaluation of passenger cars is important during early vehicle development phase as it influences fuel economy, vehicle stability and drivability. Usually during initial styling phase, scale model is prepared and tested in wind tunnel to check aerodynamic performance like drag coefficient and these are used to predict aerodynamic performance of full scale model as testing on full scale model is costly and time consuming. To ensure its correctness, it is important to understand difference in physics from scale model to full scale model. In predicting full vehicle aerodynamics performance from scale model assessment; importance of Reynolds number, effect of geometric scaling on flow i.e. flow separation and wake zone change needs to be understood and addressed. This paper discusses about effect of scaling on aerodynamic flow behavior and drag. Further, with detailed flow behavior analysis, conclusions are derived on parameters that need to be scaled or addressed to predict full scale vehicle level drag from scale model. Study is carried out on three standard bodies i.e. notchback, estate back and fast back through computational studies using commercial CFD solver and results are validated with physical wind tunnel test data.