Streamwise development and turbulence characterization of a twin-vortex inlet distortion for turbofan applications

Ground based turbofan inlet flow distortion investigations typically involve a distortion generator placed within the inlet duct to create the desired flow conditions entering the fan. The physical nature of such devices requires thorough research and analysis to ensure that any adverse effect of the test article does not interfere with or disturb the desired test conditions. A sub-scale wind tunnel experiment was conducted to study the nature of the distortion development and characterize the turbulent energy produced by a twin-vortex StreamVaneTM swirl distortion generator. Stereoscopic particle image velocimetry was employed to measure the three component velocity field at four discrete planes downstream of the StreamVane. Time-averaged results revealed that secondary flow angles decreased by as much as 25% while the centers of the twin vortex distortion pattern convected toward the centerline of the duct. Maximum secondary flow velocity magnitudes remained nearly constant in the outlet flow; however, an increase in the extent of the distortion was observed. Statistical time-resolved results indicated that a highly non-uniform turbulent flow field, with axial turbulence intensity levels exceeding 7%, was produced in the immediate downstream measurement plane; further downstream, the turbulent energy mixed to a relatively uniform intensity of approximately 4%. A POD description of the flow indicated that the turbulent length scales produced by the StreamVane wakes attenuate as the flow develops and mixes. All results from this investigation will assist in understanding the effects of submerged distortion generators as well as advance the current state of the art toward less disruptive flow conditioning devices.