Research Papers

Reduction in Flow Parameter Resulting From Volcanic Ash Deposition in Engine Representative Cooling Passages

[+] Author and Article Information
Sebastien Wylie

Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: sebastien.wylie@eng.ox.ac.uk

Alexander Bucknell, Peter Forsyth, Matthew McGilvray, David R. H. Gillespie

Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 20, 2016; final manuscript received October 4, 2016; published online November 22, 2016. Editor: Kenneth Hall.

J. Turbomach 139(3), 031008 (Nov 22, 2016) (13 pages) Paper No: TURBO-16-1248; doi: 10.1115/1.4034939 History: Received September 20, 2016; Revised October 04, 2016

Internal cooling passages of turbine blades have long been at risk to blockage through the deposition of sand and dust during fleet service life. The ingestion of high volumes of volcanic ash (VA) therefore poses a real risk to engine operability. An additional difficulty is that the cooling system is frequently impossible to inspect in order to assess the level of deposition. This paper reports results from experiments carried out at typical high pressure (HP) turbine blade metal temperatures (1163 K to 1293 K) and coolant inlet temperatures (800 K to 900 K) in engine scale models of a turbine cooling passage with film-cooling offtakes. Volcanic ash samples from the 2010 Eyjafjallajökull eruption were used for the majority of the experiments conducted. A further ash sample from the Chaiten eruption allowed the effect of changing ash chemical composition to be investigated. The experimental rig allows the metered delivery of volcanic ash through the coolant system at the start of a test. The key metric indicating blockage is the flow parameter (FP), which can be determined over a range of pressure ratios (1.01–1.06) before and after each experiment, with visual inspection used to determine the deposition location. Results from the experiments have determined the threshold metal temperature at which blockage occurs for the ash samples available, and characterize the reduction of flow parameter with changing particle size distribution, blade metal temperature, ash sample composition, film-cooling hole configuration and pressure ratio across the holes. There is qualitative evidence that hole geometry can be manipulated to decrease the likelihood of blockage. A discrete phase computational fluid dynamics (CFD) model implemented in Fluent has allowed the trajectory of the ash particles within the coolant passages to be modeled, and these results are used to help explain the behavior observed.

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Fig. 1

Dimensionless deposition rates versus dimensionless particle relaxation time and particle diameter (using experimental conditions). Annotated to include the regime change at ϕp≈5μm and results from Refs. [18] and [19].

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Fig. 2

Illustration of known VA encounters, plotted as ash concentration versus exposure time [20]. The experimental dosage line is marked as the red dotted line.

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Fig. 3

Size distributions for the VA samples S1–S6

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Fig. 4

SEM images of EYJA samples S1 (a) and S4 (b)

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Fig. 5

An isometric view of a 180 deg section through the HD90 test piece using SolidWorks

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Fig. 6

(a) Overall process flow diagram and (b) hot section of the experimental rig with labeled components: I. = in-line heater, II. = electric heater tape and insulation, III. = CDS, IV. = mixing chamber, V. = electric kiln, VI. = extractor fan

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Fig. 7

Fluctuation in test piece pressure as ash is ingested into the test piece: (a) without deposition, and (b) with deposition. The difference in pre-ingestion test piece pressure is due to different experiment metal temperatures.

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Fig. 8

Flow Parameter raw data and trend line results for the cold calibration of EYJA S2 at Tm = 1273 K

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Fig. 9

(a) Clear passages in the test piece at Tm=1193 K and (b) evidence of deposition in the passages for Tm=1253 K

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Fig. 10

(a) RFPC and (b) RFPH for various metal temperatures (c) RFP at the pre-ingestion pressure ratio as a function of metal temperature

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Fig. 11

RFPC results as a function of particle size at Tm = 1293 K

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Fig. 12

RFPC for Chaiten and EYJA ash at Tm = 1193 K

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Fig. 13

Significant number of passages blocked with the Chaiten ash sample when ingested at Tm = 1193 K

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Fig. 14

RFPC as a function of Reynolds number

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Fig. 15

RFPC as a function of volcanic ash dosage

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Fig. 16

RFPC versus PR as a function of test piece geometry and metal temperature

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Fig. 17

Geometry and main deposition location for (a) HD45 and (b) HD135

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Fig. 18

(a) Deposition in first four cooling holes of HD45, 1310 K; (b) blocked film cooling hole in HD45, 1310 K

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Fig. 19

(a) External metal temperature of the feed pipe and test section, showing the defined transition at entry to the kiln (operating at 1293 K). (b) Fluid temperature within the film cooling passage and holes, at the same external temperature.

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Fig. 20

Particle tracks in HD90, showing a cross section of the test piece at the most downstream six holes. Colored by particle diameter: blue = 3 μm; green = 10 μm; red = 15 μm.




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