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TECHNICAL PAPERS

Experimental and Numerical Investigation of the Unsteady Surface Pressure in a Three-Stage Model of an Axial High Pressure Turbine

[+] Author and Article Information
Carmen E. Kachel1

 Whittle Laboratory, Engineering Department, Cambridge University, Cambridge, UKcarmen.kachel@siemens.com

John D. Denton

 Whittle Laboratory, Engineering Department, Cambridge University, Cambridge, UK

1

Currently at Siemens PG, Mülheim, Germany

J. Turbomach 128(2), 261-272 (Mar 01, 2004) (12 pages) doi:10.1115/1.1860378 History: Received October 01, 2003; Revised March 01, 2004

This paper presents the results of a numerical and experimental investigation of the unsteady pressure field in a three-stage model of a high pressure steam turbine. Unsteady surface pressure measurements were taken on a first and second stage stator blade, respectively. The measurements in the blade passage were supplemented by time resolved measurements between the blade rows. The explanation of the origin of the unsteady pressure fluctuations was supported by unsteady three-dimensional computational fluid dynamic calculations of which the most extensive calculation was performed over two stages. The mechanisms affecting the unsteady pressure field were: the potential field frozen to the upstream blade row, the pressure waves originating from changes in the potential pressure field, the convected unsteady velocity field, and the passage vortex of the upstream blade row. One-dimensional pressure waves and the unsteady variation of the pitchwise pressure gradient due to the changing velocity field were the dominant mechanisms influencing the magnitude of the surface pressure fluctuations. The magnitude of these effects had not been previously anticipated to be more important than other recognized effects.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 7

FFT of raw signal from fast response pressure probe (traverse plane 1, midspan)

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Figure 14

Representation of a turbine wake as a negative jet (21-23)

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Figure 8

Propagation of pressure fluctuations on stator 1 surface (midspan); (a) experiment; (b) calculation; SS x∕lx PS ×2; rotor blade passing periods ×2 phat [Pa] (p̂[PA]); Exp(−S∕R); P̃−P¯∕P̂∣x

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Figure 1

Schematic of multistage turbine rig

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Figure 2

Instrumentation for time resolved static pressure measurements; (a) pressure transducer for time resolved surface pressure measurements, (b) slots for pressure sensors

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Figure 3

Instrumentation for time-mean static pressure measurements

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Figure 4

UNSTREST mesh for 2-stages and for rotor-stator calculation, quasi-stream surface, midspan; rotor-stator calculation, stator 1, rotor 1, stator 2, rotor 2

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Figure 5

Systematic of the s–t diagrams used for unsteady surface data; axial chord; time; measurement, SS, LS, PS; transducer position, wake; 1d pressure wave; upstream potential field; downstream potential field

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Figure 6

Pitchwise static pressure variation, measurement in traverse plane 1 (midspan); (a) absolute frame of reference, with bars of maximum and minimum pressure; (b) rotating frame of reference, time averaged and time resolved pressure PS SS, % stator pitch, % rotor pitch, static pressure [Pa]×2; time average; amplitude; rms

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Figure 9

Time resolved static pressure measurement p̃ in traverse plane 1 (midspan)

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Figure 10

Instantaneous pressure field at midspan of first stage, taken from 2 stage calculation: colored contours are p−p¯ field with contour interval of Δ(p−p¯)=20Pa, line contours of instantaneous pressure field p with contour interval Δp=10Pa; stator, rotor

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Figure 11

Unsteady rotor-stator calculation; quasi-orthogonal at traverse plane; top=exp(−S∕R); bottom=p̃−p¯; (a) last plane of rotor grid, showing pressure field of stator, p¯ taken from point fixed to rotor; (b) first plane of stator grid, showing pressure field of rotor, p¯ taken from point fixed to stator

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Figure 12

Unsteady rotor-stator-calculation, 85% span; (a) circumferential plane: colored contours of p̃−p¯ with increment of 20 Pa; black contours of p̃; white contours of negative û; (b) s-t diagram of p̂ (color) and exp(−S∕R) (black lines) on stator 2 surfaces; p̂ [Pa]; rotor blade passing periods; SS x∕lx PS; Exp(−S∕R)

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Figure 13

Envelope of velocity fluctuations ũ on the surface of four blade passages, taken from unsteady rotor-stator-calculation

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Figure 15

Unsteady rotor-stator-calculation, at midspan; (a) circumferential plane: colored contours of p̃−p¯ with increment of 20 Pa; black contours of p̃; white contours of negative û; (b) s-t diagram of p̂ (color) and exp(−S∕R) (black lines) on stator 2 surfaces; p̂ [Pa]; rotor blade passing periods; SS x∕lx PS; Exp(−S∕R)

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Figure 16

Propagation of pressure fluctuations on stator 2 surface; (a) experimental (midspan); (b) 2-stage calculation (58% span); SS x∕lx PS ×2; rotor blade passing periods ×2; p̂ [Pa] ×2; Exp(−S∕R); P̃−P¯∕P̂∣x

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