An Arbitrary Hybrid Turbulence Modeling Approach for Efficient and Accurate Automotive Aerodynamic Analysis and Design Optimization

Abstract

The demand in solving complex turbulent fluid flows has been growing rapidly in the automotive industry for the last decade as engineers strive to design better vehicles to improve drag coefficients, noise levels and drivability. This paper presents the implementation of an arbitrary hybrid turbulence modeling (AHTM) approach in OpenFOAM for the efficient simulation of common automotive aerodynamics with unsteady turbulent separated flows such as the Kelvin–Helmholtz effect, which can also be used as an efficient part of aerodynamic design optimization (ADO) tools. This AHTM approach is based on the concept of Very Large Eddy Simulation (VLES), which can arbitrarily combine RANS, URANS, LES and DNS turbulence models in a single flow field depending on the local mesh refinement. As a result, the design engineer can take advantage of this unique and highly flexible approach to tailor his grid according to his design and resolution requirements in different areas of the flow field over the car body without sacrificing accuracy and efficiency at the same time. This paper presents the details of the implementation and careful validation of the AHTM method using the standard benchmark case of the Ahmed body, in comparison with some other existing models, such as RANS, URANS, DES and LES, which shows VLES to be the most accurate among the five examined. Furthermore, the results of this study demonstrate that the AHTM approach has the flexibility, efficiency and accuracy to be integrated with ADO tools for engineering design in the automotive industry. The approach can also be used for the detailed study of highly complex turbulent phenomena such as the Kelvin–Helmholtz instability commonly found in automotive aerodynamics. Currently, the AHTM implementation is being integrated with the DAFoam for gradient-based multi-point ADO using an efficient adjoint solver based on a Sparse Nonlinear optimizer (SNOPT).

Computational Analysis of Actuation Techniques Impact on the Flow Control around the Ahmed Body

“…This computational study is performed using adapted Large Eddy Simulations with a particular emphasis on the signal type influence. Large Eddy Simulations are still considered as the most accurate computational approaches to simulate and control turbulent flows around such geometries [25,26]. The numerical method for the base flow is initially validated comparing to in house experiments before being generalized to controlled cases.…”

Drag Reduction on a Three Dimensional Teardrop-Shaped Body Car with Different Stagnation Points

“…Lastly, it appears that the high drag coefficient moment is always caused by the production of a more complicated or strong vortex motion. An Arbitrary Hybrid Turbulence Modeling (AHTM) was developed by Maulenkul et al [17] using a combination of Reynolds Averaged Navier-Stokes (RANS), Unsteady Reynolds Averaged Navier-Stokes (URANS), Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS) turbulence models in a single flow field based on the local mesh refinement. When compared to the traditional benchmark case of an Ahmed body, their findings indicated that the ATHM is the most precise of all turbulent models.…”