Simulation of Secondary and Separated Flow in a Serpentine Diffuser (S-Duct) for Air Breathing Propulsion

The focus of this paper is on the numerical simulation of compressible flow in a diffusing S-duct inlet; this flow is characterized by secondary flow as well as regions of boundary layer separation. The S-Duct geometry produces streamline curvature and an adverse pressure gradient resulting in these flow characteristics. The geometry used in this investigation is based on a NASA Glenn Research Center experimental diffusing S-Duct which was studied in the early 1990's. The CFD flow solver ANSYS - Fluent is employed in the investigation of compressible flow through the S-duct. A second-order accurate, steady, density-based solver is employed in a finite-volume framework. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations are solved on a structured mesh with a number of turbulence models, namely the Spalart - Allmaras (SA), k-ε, k-ω SST, and Transition SST models, and the results are compared with the experimental data. The computed results capture the flow field and pressure recovery with acceptable accuracy when compared to the experimental data. The turbulence model giving the best results is identified.