This investigation is a continuing analysis of the cooling performance and aerodynamic properties of a rear mounted cooling module on a semi-generic commercial vehicle, which was carried out by Larsson, Löfdahl and Wiklund . In the previous study two designs of the cooling package installation were positioned behind the rear wheelhouse and the results were compared to a front mounted cooling module. The investigation was mainly focused on a critical cooling situation occurring at lower vehicle speeds for a local distribution vehicle. The conclusion from the study was that the cooling performance for one of the rear mounted installation was favourable compared to the front mounted cooling package. This was mainly due to the low vehicle speed, the high fan speed and to fewer obstacles around the cooling module resulting in a lower system restriction within the installation.
The main purpose with the present investigation was to determine the power needed to overcome the aerodynamic drag together with the power needed by the fan to obtain a specific cooling performance at a higher vehicle speed. One front and three rear mounted cooling package installations were included in the analysis. The vehicle geometry was modified to be able to implement the changes for the rear cooling module installations; the design of the air inlet, air outlet and the duct in front of and after the cooling package were changed for the rear mounted cooling package installations to improve the airflow and as a result the cooling performance. The investigation was performed by the use of Computational Fluid Dynamics.
It was found that the total power required due to aerodynamic drag and fan operation to obtain a specific cooling performance was reduced for two of the rear mounted compared to the front mounted cooling module. Even though the fan for these installations required more power, the total power needed by the vehicle was decreased due to a lower aerodynamic resistance. The total power demand was reduced by 1.9kW for one of the rear mounted installations compared to the front mounted cooling package. Furthermore it was established that the design of the air inlet for a rear mounted cooling package was important to obtain a low total power demand, a high mass airflow through the cooling module and to obtain a uniform flow over the heat exchangers. For critical driving situations due to cooling performance, occurring at lower vehicle speeds, the rear mounted cooling packages also gave a favorable cooling performance compared to the front mounted cooling module installation. This was mainly due to the lower system resistance and higher static fan efficiency for these installations. To increase the cooling performance and decrease the power requirement even more the air inlet, the fan choice and the duct geometry could be further developed.