Date of Award


Publication Type

Master Thesis

Degree Name



Mechanical, Automotive, and Materials Engineering


CFD, Radiator, Simulation, Underhood


Johrendt, Jennifer




This research focuses on virtual simulation techniques for vehicle underhood airflow. The main objective is to gain a better understanding of heat transfer effects on vehicle underhood cooling airflow and provide correction methods to increase the accuracy of simulations early in the vehicle development phase. Simulations are carried out for a stand-alone radiator setup, based on three different flow assumptions; constant density iso-thermal, constant density with heat transfer, and variable density with heat transfer. It was observed that, in some cases, corrected heat exchanger porous resistance terms need to be adopted for each simulation case in order to provide good correlation with test data. Similar flow assumptions are carried over to a full vehicle underhood simulation, for which additional components, such as a transmission oil cooler, condenser, and fan were modeled. It was observed that mass flow rates at the radiator inlet are over-estimated with the assumption of an incompressible iso-thermal flow; by 2% with respect to the incompressible simulation with temperature effects, and by 10% with respect to the variable density simulation with temperature effects. It is suggested that in order to capture the local increase in velocity field at the heat exchangers, it is necessary to perform simulations with a variable density. However, to establish confidence in the quantitative results, further studies regarding the impact of fan modelling and variable density effects should be performed.