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There is a recognized need in the industry to improve the quality of our CFD (Computational Fluid Dynamics) processes. One part of that initiative is to measure the accuracy of the current processes and identify opportunities for improvement. This report documents the results of a disciplined calibration process that uses statistical analyses techniques to assess CFD quality. The process is applied to UH3D, a Navier-Stokes solver used at Ford to model vehicle front-end geometry and engine cooling systems. The study is focused on a Taurus under relatively ideal circumstances to address one of the major deliverables from the analytical process, i.e., what is the accuracy of the front-end cooling airflow predictions? To address this question, high quality isothermal experiments and calculations were conducted on twenty-three front-end configurations at four non-idle operating conditions.

This report is a contribution to the understanding of inlet aerodynamics and cooling system resistance. A characterization of the performance capability of a vehicle front-end and underhood, called the ram curve, is introduced. It represents the pressure recovery/loss of the front-end subsystem - the inlet openings, underhood, and underbody. The mathematical representation, derived from several experimental investigations on vehicles and components, has four basic terms: Inlet ram pressure recovery; free-stream energy recovered when the vehicle is moving Basic inlet loss; inlet restriction when the vehicle is stationary Pressure loss of the engine bay Engine bay-exit pressure Not surprisingly, the amount of frontal projection of radiator area through the grille, bumper and front-end structure (called projected inlet area), and flow uniformity play a major role in estimating inlet aerodynamic performance.

With the increasing emphasis on and importance of aerodynamics on vehicle fuel economy and handling, conservative approaches to sizing front-end cooling openings based on projected radiator area need to be replaced by a performance-based method. The method would not only allow more flexibility in front-end styling, but would enable the design of the grille, cooling hardware and vehicle heat rejection requirements to be based on the cooling performance of the total vehicle. The reductions in cooling drag and front lift from smaller, but more functional, grille openings would improve vehicle fuel economy and handling. A performance-based front-end design approach is described in the paper along with some selected experimental results. The method is based on an experimental technique for simultaneously measuring the total radiator airflow and vehicle aerodynamic performance in an aerodynamic wind tunnel.

This paper describes the computational technique used to predict flow over and through the front end of vehicles; this scope includes flow over the hood, around air dams, through condensers, radiators, fans, and in the engine compartment. The computational procedure, employed is a finite-difference method for solving time-averaged equations for turbulent flow using the κ-∈ model. A two-dimensional program was modified to add variable-depth cells (in the direction of car width) so that some three-dimensional features could be included. A turbulence model was used which is applicable to rotational and irrotational areas of the flow field. The total system model was calibrated with wind-tunnel data, and various modifications to the vehicle configuration were studied. Results from the predictions were compared with wind-tunnel test data.

Vehicle functional requirements, diesel emission regulations, and subsystem thermal limits all have a direct impact on the design of a powertrain cooling airflow system. Severe duty cycles, minimal ram air, fouling, and sometimes unconventional package layouts present unique challenges to the designer. This course introduces many airflow integration issues and vehicle-level trade-offs that effect system performance and drive the design. The goal of this course is to introduce engineers and managers to the basic principles of diesel cooling airflow systems for commercial and off-road vehicles.