Compressible flow characteristics in bent duct with constant flow section

The components with large curvature features are widely applied in aero-engines. Complex flow features are induced due to large curvature under high-subsonic even transonic incoming flow condition. In this study, the formation mechanisms of local acceleration in bent duct are investigated. To this end, the cold fluid test of a 60° bent duct with constant flow section was conducted. The surface static pressures and the schlieren flow visualizations were obtained. Then the three-dimensional numerical simulations based on the experimental model were computed using computational fluid dynamics software. The simulations were conducted using five different turbulence models to compare with the experimental data. The validation study shows that the shear stress transfer (SST) κ-ω turbulence model is suitably used for the simulations. Results show that three different flow situations were shown for the bent duct at diverse nozzle pressure ratios (NPRs). One situation was shown by the case at NPR = 1.5, in which the whole flow field is subsonic, and just two jet edges are shown by the schlieren images. One situation was shown by the case at NPR = 1.8, in which a local supersonic region is induced near the lower wall at the hind side of the bent section, and a small shock wave is observed. The other one situation was shown by the cases at NPR = 2.0, 2.5 and 3.0, in which the air flow in the whole passage reaches supersonic speeds and an oblique shock wave is shown for each case.