A New Approach to Model the Fan in Vehicle Thermal Management Simulations

Vehicle thermal management (VTM) simulations constitute an important step in the early development phase of a vehicle. They help in predicting the temperature profiles of critical components over a drive cycle and identify components which are exceeding temperature design limits. Parts with the highest temperatures in a vehicle with an internal combustion engine are concentrated in the engine bay area. As packaging constraints grow tighter, the components in the engine bay are packed closer together. This makes the thermal protection in the engine bay even more crucial. The fan influences the airflow into the engine bay and plays an important role in deciding flow distribution in this region. This makes modelling of the fan an important aspect of VTM simulations. The challenge associated with modelling the fan is the accurate simulation of the rotation imparted by the fan to the incoming flow. Currently, two modelling approaches are prevalent in the industry. They are moving reference frame (MRF) and rigid body motion (RBM). This paper explains the workings and drawbacks of these models in terms of simulating the fan. The study then focuses on overcoming the shortcomings of these models by developing a new method to ensure fast and accurate simulation of the fan. The method works by applying user-defined momentum sources to a disc-type region to effectively simulate the correct rotation of the incoming airflow. The applicability and modularity of the method are then improved by developing a function to simulate the fan at different speeds. This new technique reduces the time associated with accurate simulation of the fan which in turn reduces the turnaround time of VTM simulations. The results have been validated on a cooling module testbench for rotation of the temperature field downstream of the fan and show good agreement with experiment.