Inlet pressure distortion has been observed to cause changes in the operating condition of high-performance fans, often accompanied by undesirable losses in performance.  Characterization of distortion transfer and generation through fans with distorted inlet conditions enables progress towards designs with improved distortion tolerance.  Impacts on fan performance due to inlet distortion profile shape have been studied experimentally using a variety of basic screen patterns.  Recent research has shown the abruptness of transition from undistorted to distorted total pressure regions at the inlet impacts the induced swirl profile and therefore the distortion transfer and generation. 

To characterize these impacts, full annulus simulations of the AFRL Rotor 4 geometry with a variety of inlet distortion profiles are converged using STARCCM+.  Variations of a 90-degree and a 135-degree sector, both of 15% total pressure distortion, are each applied to the fan.  These sectors are representative of inlet distortion conditions that may be generated from S-duct diffusers.  We define the boundary between distorted and undistorted regions in the inlet profile based on the circumferential distance it takes to transition from clean (high) total pressure to distorted (low) total pressure. This research looked at three distortion transition variations from abrupt to gradual.

Fourier based distortion descriptors are used to quantify levels of distortion transfer and generation at axial locations through the fan, principally at the rotor exit and stator exit.  Near-stall, near-design, and choked operation points are simulated for each inlet profile and compared.  At each operating point, circumferential traverses of swirl, total pressure, total temperature, and power are compared at five radial locations from the hub to the casing.

Of interest is the relationship between induced swirl and circumferential power variation within the fan stage.  As seen in previous work by the authors, induced swirl gradients are greatest at the boundaries of the inlet distortion sector.  The peaks and valleys related to the edges of the inlet distortion are observed in the swirl, total pressure, total temperature, and power profiles. It suggests that the abruptness or smoothness of the transition from undistorted to distorted flow at the inlet to a rotor is important and will affect the amount of swirl induced, power varied, and total temperature generated.  These conclusions will be verified using a combination of qualitative contour plots, Fourier based descriptors, and circumferential traverses at the rotor inlet and outlet.  


Effects of Inlet Distortion Patterns on Induced Swirl in a Highly Loaded Fan Stage

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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