The effects of simplifications on isolated wheel aerodynamics

In order to study the aerodynamic forces and flow features of rotating wheels, compromises and simplifications are often made in wind tunnel testing, and more frequently so in numerical modelling. A CFD approach similar to that commonly used in industry was utilised to investigate common assumptions involving; the influence of geometric fidelity in wheel hub regions, ground representation, the modelling of the contact patch, and the effects of rotation on separation. It was found that the separation and wake characteristics were strongly influenced by the rotation of the wheel; the separation point changed by as much as 90% compared to a stationary wheel, and drag was close to 20% less - downforce was approximately 40% greater. In addition, the modelling of the contact patch, treated here as a small step to facilitate skew-free meshing necessary for a reliable converged result, was seen to cause up to a 52% difference in predicted lift characteristics, and an increase in the step of just 2 mm decreased the maximum wake thickness by close to 50% - considerable changes stemming from superficially-minor simplifications. Including indented wheel hubs proved to be more influential on the production of vortices and wake structures, causing the merging of previously-separate vortex structures. The results point to a need for very careful evaluation of the goals of any study when determining which simplifications can be made in both physical testing and numerical analysis. (C) 2015 Elsevier Ltd. All rights reserved.