Flow distortion reduction by blade cascades, PART 2: Experimental Validation

Serpentine ducts, commonly used in modern propulsion system designs, introduce undesirable flow characteristics such as swirl-induced distortions, adverse pressure gradients, and flow separation that can adversely affect fan stability and compressor performance. In order to be able to control the flow distortion in a serpentine duct (S-duct), Continuum Dynamics Inc. (CDI) used their flow design software to produce vane geometries optimized to generate and remove a twin vortex flow distortion typical of an S-duct inlet in a straight pipe. This paper aims at validating the numerical results of the flow distortions and control described in PART 1 of this work. To achieve that, distortion generation and removal devices using the optimized geometries were additively manufactured and tested in a benchtop experiment. Stereoscopic particle image velocimetry was employed to measure three-component velocity fields at discrete planes downstream of the devices in a small-scale low-speed wind tunnel. The comprehensive analysis presented in this completed study includes a detailed description of the experimental methods and an in-depth analysis of various flow characteristics, including in-plane velocity profiles, axial velocity magnitude contours, and swirl angles. The results show that the distortion devices with optimized blades successfully reduced the swirl distortions from 15 degrees to less than 3 degrees. When compared to the numerical results, the experiments produced lower swirl angles and showed that the wakes generated by the blades fully mix with the flow by 2D downstream of the blades. These results offer practical insights into passively controlling flow distortions in propulsion systems, paving potential applications of this approach in enhancing aerospace engineering, promising improved performance in propulsion systems.