A detailed statistical study of unsteady wake dynamics from automotive bluff bodies

There is a growing emphasis from automotive manufacturers on efficient performance, with a greater need to leverage unsteady aerodynamics data in the design process. Simplified bluff bodies are regularly used to generate flow features which replicate specific behaviour of flow around real vehicles. The unsteady aerodynamics of a squareback and a 40º slant back Windsor body was investigated here using Computational Fluid Dynamics (CFD) at Re = 2.56 × 106. The results were generated using a Lattice-Boltzmann-based Very Large-Eddy Simulation (VLES) solver and experimental measurements were taken in a static-ground, in-draft wind-tunnel. This paper compares unsteady force coefficients, base surface pressures and vortex interaction in the wake. Statistical methods were defined and applied to identify the correlation present in the sampled signals, propose improvements to the calculation of confidence intervals and understand interaction between different coherent flow features. The slant modification was found to significantly shorten the integral time-scales in the near-wake. Spectral analysis of point probes revealed that the 40º slant modification favoured higher frequency content. Independent, modified confidence intervals showed a log-linear variation with sample sizes.