Aerodynamic Design and Installation Effects of Automotive Electric Cooling Fans

Licentiate thesis, 2023

Electric cooling fans play a crucial role in automotive thermal management. They generate the airflow required for heat rejection from the expended coolant circulating within the heat exchanger. This thesis focuses on the aerodynamic design and installation effects of electric cooling fans or "E-fans". E-fans are low-pressure axial fans powered by individual electric motors due to the absence of an internal combustion engine in electric vehicles. These E-fans are often packaged very tightly due to the limited space in the underhood region. Additionally, they are often subjected to non-uniform inflow conditions as they are placed downstream of other components in the underhood region.

This thesis details the design process of low-pressure axial fans with low-solidity blades using the Blade Element Momentum (BEM) method. The design process takes into consideration the cooling system requirements. Three-dimensional, steady-state, Reynolds-Averaged Navier Stokes (RANS) simulations are performed on a single blade passage for a low-pressure axial fan rotor blade with a dimensional resemblance to the fans used for automotive cooling. The effect of an upstream blockage on the aerodynamic performance of the fan is investigated. A strong influence of the flow blockage on the aerodynamic performance is observed. A decrease in efficiency, an earlier onset of stall, and peak efficiency at lower volume rates is observed for increasing blockage of the fan face. Furthermore, the effect of installing two low-pressure axial fans in parallel on the aerodynamic performance of the fans is investigated. A circumferential non-uniformity in the flow which varies in space and time is observed at the fan inlet. However, this non-uniformity does not propagate down to the rotor blade and affect its performance. Consequently, no significant differences are observed in the operating condition of each of the fans in the two-fan installation in comparison to a single fan. This is considered as a positive outcome for vehicle manufacturers using similar multi-fan setups, where cooling fans are placed in parallel and in close proximity to one another.