Drive Cycle Simulation of A Tiered Cooling Pack Using Non-Uniform Boundary Conditions 2014-01-0654
In a tiered cooling pack, the airflow through the individual heat exchangers is determined by the package and aperture lay out. Each heat exchanger rejects heat as a function of the internal coolant flows, the cooling airflow and the air temperature. In a typical automotive cooling pack, the cooling airflow will be non-uniform in velocity and temperature due to fans, aperture geometry, exterior flows, heat exchangers and recirculation. In a drive cycle, these boundary conditions will change with vehicle operating conditions like vehicle speed, engine speed, ambient temperature, and altitude. These non-uniform conditions on the cooling pack can lead to significant errors when uniform boundary conditions are assumed in a transient simulation. This error is commonly corrected using vehicle test data.
A predictive approach, which eliminates the need for correlation vehicle testing, is presented. This methodology uses a full vehicle airflow simulation in PowerFLOW to determine boundary conditions at the entrance and exit of the cooling package at stabilized operating conditions. GT Suite is used to model the heat exchange and fluid flow within the cooling package. The radiator heat rejection is modeled solely from component characterization. The boundary conditions over the drive cycle are determined by interpolation of the PowerFLOW results and adjustment for ambient conditions. This methodology was applied to the Jaguar XJ, with a two-tier cooling pack, executing a high speed transient drive cycle at the Nurburgring circuit. This methodology predicted transient coolant temperatures to a high level of accuracy from component data and vehicle geometry.