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
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 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 1.9 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 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.