The Impact of Vehicle Front End Design on AC Performance 2013-01-0859
Vehicle front end air flow management affects many aspects of vehicle aero/thermal performances. The HVAC system capacity is greatly driven by the airflow and the air temperature received at the condenser. In this paper, front end design practices are investigated using computer simulation and full vehicle test to evaluate their effects on AC system performance.
A full vehicle 3D CFD model is developed and used to predict the airflow and temperature in underhood and around the vehicle body, and specifically the conditions entering the condenser. The condenser inlet airflow and temperature profiles from 3D CFD model are then used as inputs for the 1D AC system model. The 1D AC system model, which includes condenser, compressor, evaporator and TXV (Thermal eXpansion Valve), is developed to observe the critical AC performance indicators such as panel out air temperature and compressor head pressure. Both 3D and 1D simulation models are validated and reasonable correlation with full vehicle tests are achieved.
Four design changes to the front end are studied in this paper. They are placement of transmission oil cooler (TOC), sealing design, belly panel design and cooling fan speed. It is found that placing the TOC in front of the superheat area of condenser gives much better performance compared to placing it near the sub-cool region. Sealing around cooling package and opening up belly panel help reduce the temperature of the air entering condenser at idle, at the cost of increasing complexity and aerodynamic detriment, respectively. Finally, the sensitivity of cooling fan speed is investigated to enable the selection of the appropriate fan speed.