Investigation into natural convection in an underhood model under heat soak condition

Underhood simulations are proving to be crucially important in a vehicle development program, reducing test work and time-to-market. While Computational Fluid Dynamics (CFD) simulations for steady forced flows have demonstrated reliable, studies of transient natural convective flows in engine compartments under heat-soak (key-off condition with engine and turbocharger emitting high heat flux) are not yet carried out due high computing demands and lack of validated work. The present work aims to computationally characterize the thermally-driven flow in a simplified half-scaled underhood compartment and to experimentally determine the validity of the CFD approach. The commercial software VECTIS was employed for the numerical simulations. Surface temperatures of components as well as the spatial distribution of the air temperature were measured under both steady state and transient (cooling) condition. The airflow patterns induced by the buoyant forces were studied with Particle Image Velocimetry (PIV). Detailed comparison showed that the experimental and CFD results were in good agreement. It was suggested that the results, and more generally the techniques used for the analysis, could be employed to improve the underhood ventilation strategy and the component packaging configuration. Copyright © 2005 SAE International.