Research Papers

The Impact of Realistic Casing Geometries and Clearances on Fan Blade Tip Aerodynamics

[+] Author and Article Information
Alistair John

Department of Mechanical Engineering,
University of Sheffield,
Sheffield S1 3JD, UK
e-mail: adjohn1@sheffield.ac.uk

Ning Qin

Department of Mechanical Engineering,
University of Sheffield,
Sheffield S1 3JD, UK

Shahrokh Shahpar

Derby DE24 8BJ, UK

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 18, 2017; final manuscript received November 8, 2017; published online April 18, 2018. Editor: Kenneth Hall.

J. Turbomach 140(6), 061002 (Apr 18, 2018) (10 pages) Paper No: TURBO-17-1166; doi: 10.1115/1.4038834 History: Received September 18, 2017; Revised November 08, 2017

During engine operation, fan casing abradable liners are worn by the blade tip, resulting in the formation of trenches. This paper describes the influence of these trenches on the fan blade tip aerodynamics. A detailed understanding of the fan tip flow features for cropped and trenched clearances is first developed. A parametric model is then used to model trenches in the casing above the blade tip and varying blade tip positions. It is shown that increasing clearance via a trench reduces performance by less than increasing clearance through cropping the blade tip. A response surface method is then used to generate a model that can predict fan efficiency for a given set of clearance and trench parameters. This model can be used to influence fan blade design and understand engine performance degradation in service. It is shown that an efficiency benefit can be achieved by increasing the amount of tip rubbing, leading to a greater portion of the tip clearance sat within the trench. It is shown that the efficiency sensitivity to clearance is biased toward the leading edge (LE) for cropped tips and the trailing edge (TE) for trenches.

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Fig. 1

Casing liner trench formation

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Fig. 2

Representation of the tip topologies under investigation

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Fig. 3

Location of trench within simulation setup

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Fig. 4

A typical padram mesh across a clearance with trench

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Fig. 5

Comparison of simulation with experiment

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Fig. 6

Radial profiles versus experiment at design point: (a) PR and (b) efficiency

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Fig. 7

Tip leakage vortex highlighted by three-dimensional streamlines and slices colored by entropy

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Fig. 8

Clearance vortex formation method: (a) clearance streamlines and relative Mach no. contours and (b) schematic of vortex formation

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Fig. 9

Tip leakage distributions for various clearances

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Fig. 10

Q-criterion isocontours (108) showing change in vortex with clearance: (a) datum clearance, (b) twice datum, and (c) thrice datum

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Fig. 11

Tip region loss due to cropping blade

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Fig. 12

Variation in blade performance with clearance (due to cropping tip)

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Fig. 13

Representation of the geometry types under investigation

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Fig. 14

PR and TR variation with clearance: (a) PR and (b) TR

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Fig. 15

Efficiency variation with clearance

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Fig. 16

Tip region loss for the different cases at twice datum clearance, measured at 0.9 chord

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Fig. 17

Rel. Mach No. Contours showing the variation in vortex size at a constant radius for twice datum clearance

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Fig. 18

Variation in blockage intensity downstream of TE step for each case at twice datum clearance

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Fig. 19

The influence of trench steps (zero axial flow contours show separation)

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Fig. 20

Delta PR radial profile from twice to datum clearance for each case

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Fig. 21

Representation of the parametric definition of the geometry

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Fig. 22

Comparison of RSM fit to CFD data

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Fig. 23

Comparison of simulated and predicted performance variations with clearance

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Fig. 24

Variation of TE separation due to different clearance types




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