Analysis of the Underhood Aero-thermal Flow Features Using 3D CFD Simulations

Paper #:
  • 2017-01-0142

  • 2017-03-28
The demand for better fuel economy pushed by both the consumers and Environmental Protection Agency (EPA), made OEMs to put more effort on other areas beside vehicle external aerodynamics for. As one of these areas, under-hood aero-thermal management, has taken an important role in the new road vehicle design process due to the combination of growing engine power demands, utilization of sophisticated underhood and underbody devices, and emission regulations. The challenge of the under-hood airflow management is not only due to the complexity of under-hood compartment, but also as a result of the influence of the heat sources, like the condenser, radiator, powertrain and exhaust system, on the airflow characteristics. The temperature change of the under-hood airflow undermines the accuracy of the pure aerodynamic analysis. In this study, 3D CFD simulation was used to investigate the under-hood aero-thermal flow features. The full vehicle model with detailed under-hood components used in this study is a Hyundai Veloster. A commercial CDF code Star-CCM+ version 11.04 from CD-adapco was used to run all the simulations. Condenser and radiator were modeled as porous media. The cooling fan rotation was modeled using the moving reference frame (MRF) method. Heat exchanger models were applied on radiator core to simulate the heat transfer from the coolant to airflow. The under-hood flow feature is strongly affected by the wheel rotation. To improve the accuracy of the simulation, the wheel rotation was simulated with a moving wall boundary in combination with MRF method between the spokes. Heat source like powertrain, cooling package support, and exhaust system were applied with an initial temperature according to literature. The difference of flow pattern, pressure distribution, cooling drag and total drag between results from pure aerodynamic simulation and that from full aero-thermal simulations, indicates the necessity of aero-thermal analysis for investigating under-hood airflow pattern.
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