Investigation of the Buoyancy Driven Flow in a Simplified Underhood-Part I, PIV and Temperature Measurements

The results of thermal and flow studies for a ¼ scale model of an engine compartment are presented here. Using PIV and thermocouples, the mid-plane flow velocity and temperature of the buoyant underhood flow with engine block average surface temperature of 127°C and exhaust heaters (surface temperature ∼ 600°C) were measured. Thermocouples were also used to measure the steady-state temperature of the engine block surface and the enclosure outside and inside walls.

The airflow in the engine compartment is steady, laminar and three dimensional as predicted by the Grashof and Reynolds numbers calculated for different simple geometries comprising the engine block and its exhausts. Three dominant vortices are found to exist at the top corners of the engine compartment. Thermal measurements on the engine block and enclosure surfaces support the temperature gradients expected given the specified geometry and boundary conditions. The top surface of the engine compartment has the highest temperature due to the impingement of hot plumes rising from the exhausts. The bottom region of the flow is colder with lower flow speeds compared with the top more energetic region.