Transient Hot Shut Down, CFD Simulation Technique for Underhood Thermal Management

During initial vehicle development stages thermal robustness is of prime importance. Vehicles are required to be validated for different drive cycles based on users driving patterns and also geographical road load database. Numerical simulations play key role in identifying critical thermal issues for different systems well in advance before physical validation. Hot shut down is one such case where thermal soak phenomenon plays vital role from thermal robustness point of view and there is a need to address this phenomenon using Computational Fluid Dynamics (CFD), which in turn will reduce the development time / testing efforts considerably. This condition is of utmost importance especially when vehicle is moving at higher gradients (uphill sections). In these critical conditions, hot engine compartment starves for cooling airflow despite the fact that fan is operating at maximum speed. The sudden stoppage of vehicle after this high thermal load is known as hot shut down. Critical parts experiences peak temperatures in this condition. These temperatures play important role in designing and optimizing critical components. This paper describes methodology, which is developed to replicate real time hot shut down condition through transient CFD simulation technique in ANSYS FLUENT. Simulations are carried out for worst test conditions (low speed gradient / road load). Steady state low speed condition is simulated and followed by transient simulation which replicates real time physics occurring in hot shut down .Temperature trends of critical parts is observed and found to be qualitatively correlating. This method helps in optimizing the cooling requirement, thermal protection strategies, which finally improves thermal reliability.