Advancements in the Design of an Adaptable Swirl Distortion Generator for Testing Gas Turbine Engines

Inlet swirl distortion has recently become a major area of concern in the gas turbine engine community. Gas turbine engines are being installed in embedded installations that are downstream of increasingly complicated inlet systems, such as those used in Unmanned Aerial Vehicles (UAVs). These inlet systems can produce complex swirl patterns in addition to total pressure distortion. The effect of swirl distortion on engine or compressor performance and operability must be evaluated. The gas turbine community is developing methodologies to measure and characterize swirl distortion. There is a strong need to develop a mechanism for generating a prescribed swirl distortion intensity and pattern. Several devices such as delta wings or complex turning vanes have been proposed and used to generate swirl distortion with limited success. Reference 1 presented by the authors described a versatile swirl distortion generator design that produced a wide range of swirl distortion patterns of a prescribed strength, including bulk swirl, 1/rev, and 2/rev patterns. However, some of the generated swirl patterns produced by this swirl generator system were not stable and tended to oscillate with time. Using advanced Computational Fluid Dynamic (CFD) techniques, significant improvements were made to the swirl generator design. Through CFD, the mechanisms behind swirl generation were better understood and a swirl generator system was designed and analyzed which produces much more stable and predictable swirl distortion patterns. This paper describes the design features of this improved swirl generator system and presents CFD results detailing the type of swirl patterns that can be produced. The flexibility and adaptability of the swirl generator system to produce a wide variety of swirl patterns and intensities are also highlighted.