Convergence criteria influence in a transient Lattice-Boltzmann Aerodynamic simulation

The use of transient high-fidelity computational fluid dynamics (CFD) aerodynamic simulations in the automotive industry is a growing trend. Moreover, Lattice-Boltzmann methods popularity in CFD is increasing due to the affordability of computational power and the method efficiency in performing transient simulations. Transient simulation results are often averaged over a certain period in order to present results in a simpler manner. A key factor in the quality of both transient and averaged CFD simulations is the numerical tolerances used in the convergence criteria for each time step, aiming to get more accurate results. In this work, we present a numerical study of different numerical tolerances for the drag coefficient in a transient Lattice-Boltzmann aerodynamic simulation over a production road vehicle. Two tolerances for the drag coefficient are presented with 85% and 95% confidence interval being evaluated for the baseline case. Comparative flow results are presented in combination with estimated total computational time for each case, providing technical basis for the results and conclusions.