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Research Papers

Validation of a Numerical Model for Predicting Stalled Flows in a Low-Speed Fan—Part II: Unsteady Analysis

[+] Author and Article Information
Kuen-Bae Lee

Mechanical Engineering Department,
Imperial College London,
London SW7 2AZ, UK
e-mail: klee2@ic.ac.uk

John Dodds

Rolls-Royce plc,
Derby DE24 8BJ, UK
e-mail: john.dodds@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.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 16, 2017; final manuscript received December 14, 2017; published online April 16, 2018. Assoc. Editor: Rakesh Srivastava.

J. Turbomach 140(5), 051009 (Apr 16, 2018) (8 pages) Paper No: TURBO-17-1186; doi: 10.1115/1.4039052 History: Received October 16, 2017; Revised December 14, 2017

This paper investigates the flow near the stall boundary for a low-speed/low-pressure ratio fan. Three-dimensional, Reynolds-averaged Navier–Stokes computations are performed for a modern low speed fan rig for which extensive measured data are available. Simulations are conducted at 80% corrected speed, for which the measured constant speed characteristic contains a part with positive slope. It is shown in this paper that by using an unsteady whole assembly approach, it is possible to predict the flow for all the points on the measured constant speed characteristic (including those on the positive slope part), which is not achievable by using a single passage strategy as it would result in premature “numerical stall.” The results of the computations reveal that for the operating points on the positive slope part of the characteristic, the flow structure becomes asymmetric and hence requires a whole assembly numerical model. The type of asymmetry which appears at lower flow coefficients is similar to the multicell, part span rotating stall, which can occur on the front stages of core compressors at stable operating conditions. The numerical results showed a good correlation with the measured data in terms of stall characteristics.

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References

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Figures

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Fig. 4

(a) Time history of measured static pressure on the casing and (b) zoomed-in figure at six kulite positions around circumference

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Fig. 5

Frequency spectra measured (a) on the casing and (b) on the rotor strain gauge

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Fig. 3

Comparison of characteristic map between the computations and measurement at 80% speed

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Fig. 6

(a) Comparison of distribution of stagnation pressure at 80% speed at mass flow of 0.9 and (b) zoomed-in profiles in the top 30% of the fan

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Fig. 7

Instantaneous variation of axial velocity at midchord for mass flows of (a) 0.9, (b) 0.85, (c) 0.81, and (d) 0.7

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Fig. 9

Time histories of (a) the computed static pressure at four numerical sensors located upstream of the fan and (b) the filtered measured data at 80% speed at mass flow of 0.81

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Fig. 10

Instantaneous static pressure (Δp′) contours at midchord at different time: (a) 56.3 and (b) 56.5 revolutions at 80% speed at mass flow of 0.81

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Fig. 8

Circumferential modes at midchord at (a) 99% and (b) 60% radial heights for mass flows of 0.7, 0.81, 0.85, and 0.9

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Fig. 12

Transient solution at midchord at 99% span when the mass flow is changed from 0.9 to 0.85: (a) axial velocity and (b) spatial mode

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Fig. 11

Comparison of frequency spectra between (a) CFD and (b) experiment according to the mass flow on the positive part of the characteristic

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Fig. 14

Transient solution at midchord at 99% span when the mass flow is changed from 0.81 to 0.75: (a) axial velocity and (b) spatial mode

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Fig. 13

Transient solution at midchord at 99% span when the mass flow is changed from 0.85 to 0.81: (a) axial velocity and (b) spatial mode

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Fig. 2

Measured and computed distribution of steady stagnation pressure downstream of rotor: (a) design working line (m¯ = 1.07) and (b) stall side (m¯ = 0.95)

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Fig. 1

Domain used for the unsteady computations

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