Numerical Approach to Define Hot Shut Down Strategy for Vehicle Underhood Thermal Management

At the early phase of vehicle architecture development, thermal management is of extreme importance. Every vehicle needed to be validated for different duty cycles based on the vehicle users usage pattern and geographical load conditions. Numerical analysis place critical role in identifying critical thermal issues for different system and subsystems well in advance before physical validation. Hot shut down is one of the thermal soak phenomena that plays major role in various thermal robustness point of view and that creates the need of computational fluid dynamics (CFD) to provide rapid concepting and safe virtual testing environment, that save huge amount of physical testing of the vehicle. The condition becomes worst for the off road vehicle design when cooling fan moves all the time and keep the underhood compartment cool even when the vehicle operation is stationary, however the underhood compartment becomes very warm as soon as hot shut down appears in the machine. This paper describes the methodology, developed to replicate real time hot shut down condition through transient CFD simulation technique in commercial CFD software. Simulation are carried out for worst test condition (i.e. high ambient, no speed, maximum exhaust temperature). The simulation was carried out for complete duty cycle i.e. steady state full load condition followed by transient hot shut down. Temperature trends of critical parts are observed and found to be qualitatively correlating. This method helps in optimizing the cooling requirement, thermal protection strategies that finally improves thermal reliability.