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Research Papers

Effects of Inlet Disturbances on Fan Stability

[+] Author and Article Information
Kuen-Bae Lee

Mechanical Engineering Department,
Imperial College London,
London SW7 2AZ, UK
e-mails: kuenbae.lee@imperial.ac.uk;
kuen-bae.lee@rolls-royce.com

Mark Wilson

Rolls-Royce plc,
Derby DE24 8BJ, UK
e-mail: mark.wilson@rolls-royce.com

Mehdi Vahdati

Mechanical Engineering Department,
Imperial College London,
London SW7 2AZ, UK
e-mail: m.vahdati@imperial.ac.uk

1Corresponding author.

2Present address: Rolls-Royce plc, Derby DE24 8BJ, UK.

Manuscript received November 20, 2018; final manuscript received November 28, 2018; published online December 24, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(5), 051014 (Dec 24, 2018) (11 pages) Paper No: GTP-18-1703; doi: 10.1115/1.4042204 History: Received November 20, 2018; Revised November 28, 2018

This paper investigates the effects of inlet disturbance caused by crosswind on a fan blade operation and addresses the possible aerodynamic instabilities, which can arise for such a fan-intake system. The work is carried out by using a three-dimensional unsteady computational fluid dynamics (CFD) model (AU3D), and for a modern low-speed fan rig for which extensive measured data is available. The computational domain includes the fan with outlet guide vanes for the bypass flow, engine-section stators for the core, and a symmetric intake upstream of the fan (a whole low-pressure domain). The unsteady full annulus simulations under crosswind are performed to analyze the effects of inlet disturbances on the operation of this blade. It was observed that, for sufficiently high amplitudes of crosswind, the intake lip separates, and results in a significant loss of stall margin. Moreover, even in the absence of lip separation, the blade can still stall prematurely due to nonhomogeneous flow caused by the two contra-rotating trailing vortices. In the second phase of this study, the effects of fan loading on the suppression of flow separation in the intake, and the consequent stall margin of the fan blade, were explored. The results indicated that, as the fan speed increases, it becomes more capable of reducing the inlet distortion levels, and consequently, the loss in stall margin decreases.

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Figures

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Fig. 4

Comparison of DC60 prediction—measured data (RR Internal Report IPCR38228)

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Fig. 2

Domain used for crosswind computations

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Fig. 9

Comparison of total pressure distribution at U* of 6.1: (a) experiment [7] and (b) CFD

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Fig. 5

Intake geometry for validation [7,8]

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Fig. 3

Intake geometry for validation

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Fig. 6

Comparison of vortex circulation against crosswind [8]

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Fig. 7

Comparison of xy velocity vectors with vorticity contours at U* of 18.3: (a) experiment [7] and (b) CFD

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Fig. 1

Criteria for vortex formation around intake under crosswind condition [15,16]

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Fig. 8

Comparison of DC60 against crosswind [8]

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Fig. 13

Schematic diagram around an intake: (a) side view and (b) plane view

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Fig. 10

Characteristic map for the benchmark fan blade

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Fig. 11

Measured and computed distribution of stagnation pressure at normalized mass flows of (a) 1.07 and (b) 0.95 at speed B

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Fig. 12

Measured and computed distribution of stagnation pressure at normalized mass flows of (a) 1.31 and (b) 1.17 at speed C

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Fig. 14

Comparison of characteristic map between 0XW and 3XW at speed B and C

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Fig. 15

Comparison of Mach contours around intake lip for (a) 0XW (m¯ = 0.98) and (b) 3XW (m¯ = 0.95)

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Fig. 16

Comparison of transient and instantaneous solutions at (a) 0XW and (b) 3XW

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Fig. 17

Comparison of DC60 between 2.3XW and 3XW against mass flow at speed B

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Fig. 18

Loss of stall margin at speed B against DC60 (a) and total pressure contours at fan face (b)

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Fig. 19

Streamlines around intake (a) and swirl angle upstream of fan (b) for DC60 of 0.045

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Fig. 20

DC60 values against U*

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Fig. 21

Total pressure contours at fan face according to rotation speeds on the HWK line: (a) speed A, (b) speed B, and (c) speed C

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Fig. 22

Comparison of loss of stall margin for speeds B and C against DC60

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