Investigation of RANS reliability for transonic airfoils

The principal topic of this internship has been the investigation of the reliability of 2D numerical simulations in predicting the flowfield for airfoils with a strong aft-camber. Recently, a wind tunnel test campaign was carried out by Airbus for supercritical airfoils at different transonic conditions. The results of this campaign were analysed at ONERA and a large inconsistency between numerical and experimental results was found. Following the previous analyses, this internship aimed at quantifying this inconsistency between CFD (Computational Fluid-Dynamics) and experimental data, to propose an approach that could improve numerical predictions, by assimilating the constants of the Spalart-Allmaras turbulence model, and, finally, to analyse the effects of the assimilated constants on the boundary layer properties. The main tools used are numerical-type: the "elsA" and "ISES" CFD codes, Python, the BIRDIE optimisation code and the post-processing software called TEC360. First, a wing profile capable of reproducing a mismatch between ISES and elsA has been designed, with the characteristic of having a strong aft-camber. Hence, the numerical results have been validated by a mesh convergence study. The inconsistency "mapping" has been performed over a wide range of aerodynamic conditions and geometries. The assimilation of the Spalart-Allmaras model constants, automated by a Python code written by the author of this text, and the analysis of the boundary layer have been carried out at the end of this internship. The mapping exercise showed that for profiles with an important aft-camber, CFD codes are alarmingly unable to calculate the pressure field for a wide range of aerodynamic conditions. Data assimilation has led to improvements in predicting the motion field, including pressure and friction distribution. However, a limited number of "constants" have been found to be appropriate for data assimilation, and their effects on the boundary layer of canonical flows, as a flat plate under subsonic conditions, have been found to be quite deteriorative with respect to the reference cases. Conclusively, A PhD thesis has been proposed on the subject, where a reformulation of the RSM model will be used as the object of data assimilation.