The massive flow separation in a three-dimensional S-shaped rectangular air intake is investigated using RANS and hybrid RANS/LES approaches in order to provide insights on the interplay between the corner vortices and the flow separation induced by the curvature of the duct. Experimental data from the ONERA S19Ch wind tunnel as well as a reference Zonal Detached Eddy Simulation (ZDES) mode 3, that is a Wall Modeled Large Eddy Simulation (WMLES) simulation, are employed to improve the analysis and physical interpretation of RANS and hybrid RANS/LES simulation results. It is shown that all RANS calculations, using several non-linear RANS closures including a Reynolds Stress Model (RSM) and recent Quadratic Constitutive Relation (QCR) variants, fail to reproduce the recirculation bubble in the symmetry plane, observed in the experiments and accurately simulated by the WMLES approach. The use of ZDES mode 2 (2020) -which is a hybrid RANS/LES approach where the attached boundary layers are treated in RANS mode- significantly improves the prediction of first and second-order statistics, capturing the salient flow features of the present case including a successful prediction of both the separating/reattaching dynamic and the separation line. An interpretation of the results in terms of Prandtl’s secondary flows is presented. The competition between turbulence-driven secondary flows of second kind and curvature-induced secondary flows of first kind is underscored, which also provides a better understanding of the turbulence modeling requirements for the present case. • Corner vortices and massive flow separation within a 3D S-shaped rectangular duct. • Assessment of RANS with several QCR variants and hybrid RANS/LES approaches. • Comparisons rely on experimental and WMLES reference data. • Improved accuracy achieved with ZDES mode 2 (2020) based on SST-QCR turbulence model. • Identification of Prandtl’s secondary flows of first and second kind.
Prudenzano et al. (Wed,) studied this question.