Developing a Theory for Active Grille Shutter Aerodynamics-Part 2: Effect of Flap Thickness and Shape 2019-01-5095

A recently developed theory for the description of the aerodynamic behaviour of active grille shutters is extended by the influence of the thickness of the cooling air flaps. The analysis of the resulting equations shows that the thickness of the flaps has no influence on the characteristic curve of an active grille shutter. To validate the theoretical results, wind tunnel measurements are carried out on a vehicle with an active grille shutter, and both the thickness and the shape of the flaps are specifically modified. The experimental results confirm the analytical results and show that not the thickness but the shape of the cooling air flaps is the decisive influencing factor. The experiments further show that aerodynamically unfavourable flap shapes, even with small relative thicknesses, lead to a significant change in the characteristic curve and to significant losses in cooling airflow with fully opened flaps. In contrast to this, with flow-optimized flap shapes, relative thicknesses of up to 30% of the flap length are possible without changing the characteristic curves or significantly reducing the cooling airflow rate.