Research Papers

Nonaxisymmetric Stator Design for Boundary Layer Ingesting Fans

[+] Author and Article Information
Ewan J. Gunn

Turbostream Ltd,
3 Charles Babbage Road,
Cambridge CB3 0GT, UK
e-mail: ewan@turbostream-cfd.com

Cesare A. Hall

Whittle Laboratory,
University of Cambridge,
1 JJ Thomson Avenue,
Cambridge CB3 0DY, UK
e-mail: cah1003@cam.ac.uk

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received December 20, 2018; final manuscript received March 26, 2019; published online April 15, 2019. Assoc. Editor: Kenneth Hall.

J. Turbomach 141(7), 071010 (Apr 15, 2019) (9 pages) Paper No: TURBO-18-1356; doi: 10.1115/1.4043343 History: Received December 20, 2018; Accepted March 27, 2019

In a boundary layer ingesting (BLI) fan system, the inlet flow field is highly nonuniform. In this environment, an axisymmetric stator design suffers from a nonuniform distribution of hub separations, increased wake thicknesses, and casing losses. These additional loss sources can be reduced using a nonaxisymmetric design that is tuned to the radial and circumferential flow variations at exit from the rotor. In this paper, a nonaxisymmetric design approach is described for the stator of a low-speed BLI fan. First, sectional design changes are applied at each radial and circumferential location. Next, this approach is combined with the application of nonaxisymmetric lean. The designs were tested computationally using full-annulus unsteady computational fluid dynamics (CFD) of the complete fan stage with a representative inlet distortion. The final design has also been manufactured and tested experimentally. The results show that a 2D sectional approach can be applied nonaxisymmetrically to reduce incidence and diffusion factor at each location. This leads to reduced loss, particularly at the casing and midspan, but it does not eliminate the hub separations that are present within highly distorted regions of the annulus. These are relieved by nonaxisymmetric lean where the pressure surface is inclined toward the hub. For the final design, the loss in the stator blades operating with BLI was measured to be 10% lower than that for the original stator design operating with undistorted inflow. Overall, the results demonstrate that the nonaxisymmetric design has the potential to eliminate any additional loss in a BLI fan stator caused by the nonuniform ingested flow field.

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Fig. 1

The problem—stator exit wakes for a fan operating within the BLI distortion

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Fig. 2

The solution—nonaxisymmetric stator design with varying camber, chord, and lean

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Fig. 3

Meridional view of the fan rig showing measurement plane locations

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Fig. 4

Measured and target inlet velocity profile

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Fig. 5

3D CFD domain for the BLI fan rig operating with the measured inlet stagnation pressure profile

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Fig. 6

Blade-to-blade view of a midspan sector of the nonaxisymmetric grid and flow solution: (a) nonaxisymmetric grid and (b) instantaneous axial velocity

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Fig. 7

Measured (lines with points) and computed (lines without points) flow angles at stator inlet (station 4)

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Fig. 8

Effect of nonuniform axial velocity on stator incidence in a BLI fan [1]

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Fig. 9

Measured and computed stagnation pressure distribution at stator exit (station 5): (a) measured and (b) computed

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Fig. 10

Stator section geometry parameters

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Fig. 11

Schematic describing the nonaxisymmetric stator section design approach

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Fig. 12

Stator inlet metal angle and axial chord distributions for the 2D Redesign

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Fig. 13

Computed flow field at stator exit for a nonaxisymmetric design employing variations in section inlet angle and chord (2D Redesign)

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Fig. 14

Variation of the blade stacking axis for the baseline and the 3D Redesign

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Fig. 15

Computed and measured stagnation pressure contours downstream of the 3D Redesign: (a) computed and (b) measured

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Fig. 16

Photograph of the final nonaxisymmetric stator assembly (looking aft onto leading edges)

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Fig. 17

Comparison of overall stator loss coefficients for axisymmetric and nonaxisymmetric designs



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