Assessment of Rotating Wheel Vehicle Aerodynamics Simulation using Cartesian Grid Method and Open-grill Full Vehicle Models 2019-01-0660
In vehicle aerodynamics analysis considering actual traveling conditions, it is known that the flow around the rotating wheel interferes with the wake of the wheel arch, the flow ejected from the engine room, and the flow under the floor, which significantly affects the aerodynamic drag value. In particular, the fuel consumption measurement method by World Wide Harmonized Light vehicles Test Procedure has been carried out since FY 2018 in Japan, a test condition measured by computational fluid dynamics is required to be accompanied with wheel rotation.
However, it is not easy to carry out simulation with wheel rotation for the full vehicle model using general purpose method with unstructured grid or voxel lattice, and it has a problem to perform calculation faster and easier. On the other hand, authors have proposed a method for complex geometries using hierarchical Cartesian grid and the topology-independent immersed boundary method, making it possible to handle 'dirty' CAD data directly. Several research results on the full vehicle aerodynamics have been reported with high parallel computing efficiency and high practicality. In this study, this method is applied to vehicle aerodynamics analysis with wheel rotation, and compared with experimental values measured by wind tunnel with moving belt facility.
Full vehicle aerodynamics analysis has been performed on 6 configurations and the difference in aerodynamics forces has been predicted. The grid resolution was about 6 mm, the number of computational grids was about 100 million, and calculation time for unsteady flow of 2 seconds took about 15 hours. As a result, the drag value could be predicted within the range of ΔCdA ± 0.015. In addition, a difference in the flow field around the rotating wheel was observed due to the difference in the numerical configuration of the rotation condition.