Aerodynamic flow around a sport utility vehicle—Computational and experimental investigation

Standard CFD methods require a mesh that fits the boundaries of the computational domain. For a complex geometry the generation of such a grid is time-consuming, and often requires modifications to the model geometries particularly when one begins with the “raw” CAD data. This paper evaluates the newly developed Immersed Boundary (IB) approach which does not require mesh to be conformal to body and thus would speed up the process of the grid generation. The IB approach starts directly from CAD (STL) files, and has the potential in mitigating the process of CAD cleanup and surface meshing for the CFD simulations. The Reynolds-Averaged Navier–Stokes (RANS) solver based on the Immersed Boundary technique is used to investigate the aerodynamic flow field around a generic Sport Utility Vehicle (SUV). The simulations are compared with the experimental data for the same vehicle geometries. The experimental data include particle image velocimetry (PIV) velocity, surface pressure and drag coefficient measurements. The results show that the CFD simulations were able to track the flow very well for the generic SUV (both qualitatively and quantitatively). The predicted drag coefficients for the generic SUV model was within 5% of the measured values. Finally, the IB approach was used to predict the flow structures and the drag coefficient for a production SUV (Chevy Tahoe). In addition, the same geometry was simulated using the standard body-fitted approach for direct comparison with the IB simulations. The flow results of both simulations were similar. The simulated drag coefficients for the IB and the body-fitted approaches were within 3% and 3–7% of the measured value, respectively. It should be noted that, the paper is about a comparison of the IB to body-fitted approaches for automotive aerodynamics, and these approaches are simulations of wind tunnel measurements. Since the wind tunnel testing is a cold process using an “engine-off” condition, there was no need to perform the simulations with thermal boundary conditions activated for engines, exhaust, heat exchangers, etc.