Study of Cooling Drag Reduction Method by Controlling Cooling Flow 2014-01-0679
As the demand for improved fuel economy increases and new CO2 regulations have been issued, aerodynamic drag reduction has become more critical. One of the important factors to consider is cooling drag. One way to reduce cooling drag is to decrease the air flow volume through the front grille, but this has an undesirable impact on cooling performance as well as component heat load in the under-hood area. For this reason, cooling drag reduction methods while keeping reliability, cooling performance and component heat management were investigated in this study.
At first, air flow volume reduction at high speed was studied, where aerodynamic drag has the greatest influence. For vehicles sold in the USA, cooling specification tends to be determined based on low speed, while towing or driving up mountain roads, and therefore, there may be extra cooling capacity under high speed conditions.
In order to decrease airflow volume by front grille opening area reduction, radiator efficiency improvement was investigated. Efficiency improvement enables a decrease in air flow volume without a corresponding reduction in cooling performance. It is known that high airflow velocity distribution on the radiator face causes a reduction in overall heat rejection performance. Methods to reduce this variability of face velocity distribution were studied in order to improve radiator heat rejection efficiency, and through these methods, total airflow volume through the radiator could then be decreased without adverse effects to cooling performance.
This airflow volume reduction, although acceptable for cooling performance, creates a problem for component heat load management. Component heat load is represented as a total number of hours spent at a representative temperature. Airflow control was designed in order to balance the combined low and high speed component heat load.
Several methods were investigated, including external body flow modification, cooling fan control logic, and fan shroud shape change. Cooling drag reduction was then estimated based on this cooling airflow volume change.