Streamvane turbofan inlet swirl distortion generator: Mean flow and turbulence structure

Engine/airframe integration in advanced aircraft concepts must account for nonuniform flows ingested by turbofan engines. In this work, flow details from a vane-based distortion generator were analyzed for turbulence structure and aerodynamic scaling of the mean flow. Experimental results were obtained using particle image velocimetry in a small-scale facility and a full-scale research turbofan engine for the same vane geometry. Tests were performed at nearly the same Mach number to isolate Reynolds number effects, but analysis and prior work indicate that the flow development downstream of the vanes is Mach number independent in the subsonic regime. As hypothesized from inviscid vortex dynamics, the secondary mean flow angles were consistent across scales, indicating Reynolds number independence of the large-scale secondary flow profile generated. Vane wakes produced a complex structure in the streamwise velocity component not seen in the streamwise vorticity, which resembles the distribution from the desired secondary flow profile. The most intense turbulence is concentrated in the outer radial regions of the duct and, as shown by contrast to vane wake-dominated regions, is dominated by shear flow turbulence and unsteadiness due to the distortion profile itself rather than vane wakes. Taken together, these results provide fundamental understanding of the aerodynamics of swirling flows needed for implementing complex turning vanes in the design of distortion generators.