Improved Robustness for Numerical Simulation of Turbulent Flows around Civil Transport Aircraft at Flight Reynolds Numbers

Abstract

This work aims at providing numerical methods that enable the robust and efficient simulation of turbulent flows around civil transport aircraft configurations at flight Reynolds numbers. The combined utilization of a computational and a theoretical approach for the systematic investigation of the numerical treatment of turbulence equations characterizes the work at hand. Robustness problems in case of multigrid treatment of advanced transport equation turbulence models have been identified to prevent convergence of simulations at high or flight Reynolds numbers. Therefore the application of multigrid to the turbulence equations is omitted while the multigrid treatment of the RANS equations stays unchanged. Moreover, a fully implicit time integration scheme - a DDADI approach - is applied to the turbulence equations. This approach was inspired by a systematic investigation of the numerical treatment of turbulence equations utilizing two dimensional computations and Fourier analyses. This study clearly demonstrated a destabilizing effect of productive (turbulence) source terms which is amplified in the framework of multigrid. Finally, both the original and the improved FLOWer code has been applied to two and three dimensional test cases of industrial relevance and the respective results are compared. The new approach raised robustness to a sufficient niveau to converge viscous computations at flight Reynolds numbers. Furthermore, the convergence speed of aerodynamic coefficients for three dimensional applications has also been improved significantly.