Effect of a Bypass on the Aerodynamic Characteristics of Active Grille Shutters

Vehicles with active grille shutter (AGS) systems often have bypass and leakage situations that influence the aerodynamic effectiveness and characteristics of the AGS. Precise knowledge of these characteristics, that is, the functional relationship between drag, cooling airflow rate, and degree of opening of an AGS is a prerequisite for optimum aero-thermodynamic integration into the overall vehicle. However, relatively little is yet known about the interaction of bypass and leakage flows with AGS systems. The present work therefore investigates how a bypass affects the aerodynamic characteristics of AGS. The starting point is a recently developed theory that allows an analytical prediction of the aerodynamic behavior of AGS based on the opening characteristic. This theoretical approach is first extended to the case with bypass and matched against experimental data from a real vehicle with AGS bypass configuration. The comparisons between theory and experiment lead to two semiempirical correction methods, which are validated using data from further real vehicles and which can be used to describe the influence of a bypass satisfactorily. The results of the experimental and theoretical investigations provide a detailed insight into the mode of action of a bypass. It is shown that the combination of an AGS with a bypass leads to a decrease in the authority of the AGS and thus to a shift in the characteristic curve. As a result, to achieve a defined degree of throttling in the presence of a bypass, a significantly higher degree of closure of the AGS is required. The results also explain the influence of leakage at an AGS and the behavior of systems with multiple AGS modules, where the individual modules are opened one after the other. The developed correction methods, in conjunction with the opening characteristic or the degree of opening of an AGS, allow both the theoretical prediction of the aerodynamic characteristics of AGS bypass configurations and the optimization of the opening or closing strategy of AGS systems consisting of several AGS modules.