Continuing Cooling Performance Investigation of a Rear Mounted Cooling Package for Heavy Vehicles

Paper in proceeding, 2011

This investigation is a continuing analysis of 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 [1]. 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 distribution vehicle. The conclusion from the study was that the cooling performance for one of the rear mounted installation was favorable 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 with a vehicle operating at 90 km/h were included in the analysis. The study 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 installation 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 decreased by 1.9 kW 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 flow of air through the cooling module and to obtain an uniform flow over the heat exchangers. For a critical driving situation due to cooling performance, occurring at lower vehicle speeds, the rear mounted cooling packages were also favorable due to cooling performance compared to the front mounted cooling module installation. This was mainly due to the lower system resistance and higher static fan efficiency received for these installations. To increase the cooling performance and decrease the required power even more the air inlet, the fan choice and the duct geometry can be further developed.