For higher driving velocities, the fan acts like an additional resistance and reduces the effective cooling mass flow. To avoid that effect, air flaps are included in the shroud. These flaps open in case of an “overblown” fan and the cooling air flow can directly pass by this flaps.
The air flaps are modeled by area resistances, their pressure loss characteristic is defined by a velocity depended map. To adjust the mass flow distribution between the air flaps and the shroud (fan), additional Build in Resistances (BiR) were used for the lower part of the radiator. The ratio of the resistances will directly influence the mass flow distribution.
In case of a fan driven air mass flow, the air flaps are closed. Therefore the resistance of the flaps in comparison to the BiR is very high. In case of an overblown fan (usually at high driving speeds) the resistance of the BiR is very high, in contrast the resistance of the open air flaps (area resistance) is quite small.Usable from release: KULI 9.1-0.01