Stereoscopic PIV Measurements of Swirl Distortion on a Full-Scale Turbofan Engine Inlet

TLDR: Results indicate that the methods developed may be used to both generate and characterize complex distortion profiles at the aerodynamic interface plane, providing new information about airframe/engine integration.

Abstract: There is a present need for simulating and measuring the inlet swirl distortion generated by airframe/engine system interactions to identify potential degradation in fan performance and operability in a full-scale, ground testing environment. Efforts are described to address this need by developing and characterizing methods for complex, prescribed distortion patterns. A relevent inlet swirl distortion profile was generated by a novel new method, dubbed the StreamVane method, and measured in a small scale tunnel using stereoscopic particle image velocimetry (PIV) as a precursor for swirl distortion generation and characterization in an operating turbofan research engine. The StreamVane prototype tested was made of ABS plastic using additive manufacturing and was used to generate swirl distortion patterns that mimick boundary layer ingesting engine inlets with a pair of tightly wound vortices and swirl angle magnitudes up to 15°. Diagnostic development efforts for distortion measurements within the research engine paralleled the StreamVane characterization. The system used for research engine PIV measurements is described along with data obtained in the wake of a total pressure distortion screen for engine conditions at idle and 80% corrected fan speed engine power settings. Data reduction algorithms are put forth to reduce spurious velocity vectors and uncertainty estimations specific to the inlet distortion test rig are made. Results indicate that the methods developed may be used to both generate and characterize complex distortion profiles at the aerodynamic interface plane, providing new information about airframe/engine integration.