Renault, SA, and the Laboratoire d'Aerodynamique, Conservatoire National des Arts et Métiers, both of Paris, France, used FLUENT to model the air flow under the hood of an encapsulated automotive engine in the Renault Mégane. The goal of this analysis was to illustrate the effectiveness of CFD as a tool for predicting aerodynamics transfer in this critical area of the engine, and its usefulness as a decision support for engine compartment design.

Current design trends with emphasis on low fuel consumption and reduced vehicle noise make encapsulated engines a popular option. These engines have very few external air passages, so air-flow under the hood must be studied carefully, preferably early in the design process. Using FLUENT, Renault engineers aimed to show that they could optimize the functional layout of the engine compartment, boost the efficiency of radiators, and achieve encapsulation techniques, all at a significant savings in cost and lead-time.

A geometry of the front-end of the vehicle and engine compartment was obtained from CAD definitions, and meshed with Fluent’s TGrid software. The analysis involved comparing a variety of front-end geometries and engine encapsulation techniques. The results were used to identify and compare the flow rates at the radiator air inlets and various areas of the engine compartment, highlighting the leakage rates. A particle tracking analysis of air flow further enhanced the results.

Wind tunnel experiments validated Renault's test case, proving the reliability of this method of predicting under-hood aerodynamics transfer. This technique is now an integral part of the Renault vehicle development process.

Velocity vectors colored by velocity magnitude show the air flow under the hood of an automotive engine.

Reference: P. Gilliéron, S. Samuel and F. Chomaton; Potential of CFD in Analysis Under-Bonnet Airflow Phenomena, SAE Congress, Detroit, Michigan, USA, March,1999.

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