Impact of radiator installation on noise reduction strategies for automotive engine cooling fans

This study investigates, with high-fidelity numerical simulations, how the effectiveness of noise reduction technologies, conventionally developed and tested for isolated fans, is affected when they are coupled with a radiator since the influence of such installations on fan noise reduction technologies is still poorly documented. Two noise reduction strategies are investigated to reduce two different noise sources. The first aims at reducing the backflow by redesigning an ad-hoc rotating ring; the second aims at reducing rotor-stator interaction by optimizing the stator vanes azimuthal distribution with a genetic algorithm. In the isolated fan, the new ring reduces broadband noise by redirecting the backflow radially, achieving an Overall Sound Pressure Level (OASPL) reduction of four dBA. The optimized vane spacing further decreases tonal noise by up to 10 dBA. The new ring alters the operating point by increasing the volume flow rate by 6% while increasing the aerodynamic torque by 10% due to its larger aerodynamic surface. When the radiator is installed, the flow confinement caused by the radiator casing does not allow an effective backflow redirection with the new ring, resulting in an OASPL increase of two dBA, while vane spacing still suppresses tonal harmonics by up to three dBA. Aerodynamic performance remains within 3% of the baseline, thus being less sensitive to geometry modifications with respect to the isolated fan configuration. These results demonstrate that installation effects can significantly alter the effectiveness of fan noise reduction technologies and, if designed for a free-field environment, should therefore be considered at design.