Effect of Pressure Losses and Reynolds Number on Active Grille Shutter Characteristics and Its Prediction

<div class="section abstract"><div class="htmlview paragraph">In the present article it is investigated why active grille shutters (AGS) can have very different aerodynamic characteristics, ranging from progressive to strongly degressive, and which factors influence them. For this purpose, the authority concept known from the field of heating, ventilation, and air-conditioning (HVAC) is referred to. According to this theory, the control characteristics of dampers depend primarily on the ratio of the pressure losses at the fully open damper to the pressure losses of the rest of the system. The adaptation of the concept to the automotive field shows that, in addition to the pressure losses, the geometry of the cooling air ducting plays a decisive role in motor vehicles. The effect of driving speed and fan operation on the characteristic curves is also being investigated. In addition, authority theory can also be used to derive the conditions under which the opening characteristic curve of an AGS provides a good prediction of the real characteristic curve. And finally, the authority theory offers the possibility of predicting the AGS characteristics in detail. To this end, a concept is being developed that draws on suitable inherent reference characteristics of control dampers from the HVAC sector. The practical application of the concept will be demonstrated using various examples of AGS from real vehicles. The comparison of the predicted characteristic curves with the measured data shows good agreement, with characteristic curve details also being reproduced. A prerequisite, however, is the knowledge of the pressure losses of the AGS in the fully open state as well as the pressure losses of the remaining cooling air duct. For this purpose, a method is shown, which can be used to estimate the relevant pressure losses. Overall, this provides a new calculation method that can be used to estimate the aerodynamic characteristics of AGS in the early development phase of motor vehicles.</div></div>