Aerodynamic Investigation of Cooling Drag of a Production Sedan Part 2: CFD Results 2017-01-1528

Cooling drag is a metric that measures the influence of air flow travelling through the open grille of a ground vehicle on overall vehicle drag, both internally (engine air flow) and externally (interference air flow). With the interference effects considered, a vehicles cooling drag can be influenced by various air flow fields around the vehicle, not just the air flow directly entering or leaving the engine bay. For this reason, computational fluid dynamics (CFD) simulations are particularly difficult. With insights gained from a previously conducted set of experimental studies, a CFD validation effort was undergone to understand which air flow field characteristics contribute to CFD/test discrepancies. A Lattice-Boltzmann Large Eddy Simulation (LES) method was used to validate several test points. Comparison using integral force values, surface pressures, and cooling pack air mass flows was presented. The test points include cooling pack configuration changes, underbody shield changes and vehicle attitude changes. Select test points were compared in both static and moving ground wind tunnel conditions. This paper represents the second of a two-part effort, with experimental and numerical foci respectively.