An Extensive Validation of an Open Source Based Solution for Automobile External Aerodynamics

The number of computational fluid dynamics (CFD) simulations performed during the vehicle aerodynamic development process continues to expand at a rapid rate. One key contributor to this trend is the number of analytically based designed experiments performed to support vehicle aerodynamic shape development. A second contributor is the number of aerodynamic optimization studies performed for vehicle exterior components such as mirrors, underbody shields, spoilers, etc. A third contributor is the increasing number of “what if” exploratory studies performed early in the design process when the design is relatively fluid. Licensing costs for commercial CFD solutions can become a significant constraint as the number of simulations expands. A number of alternative products (e.g., independently developed, supported and documented forks of the popular open-source OpenFOAM® toolbox [1]) have become available in recent years, offering a lower cost alternative to traditional commercial CFD products. This paper summarizes results from a broad and deep evaluation of the capability of iconCFD® to substitute for the more traditional commercial CFD solutions currently used to support vehicle aerodynamic development early in the program development cycle. Included in this study were detailed B-car, sedan, SUV and truck shapes as well as multiple variants of each shape. The study investigated both static and moving ground boundary conditions as well as alternative turbulence models. Trends of the predicted aerodynamic drag coefficients (C_d) are compared against experimental data. Both transient and steady state simulation ranking accuracy of total vehicle C_d were found to be equivalent to that historically observed with more traditional commercial solver results. A consistent upward bias in absolute C_d values was observed in the transient results.