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Research Papers: Gas Turbines: Turbomachinery

Unsteady Wet Steam Flow Field Measurements in the Last Stage of Low Pressure Steam Turbine

[+] Author and Article Information
Ilias Bosdas

Laboratory for Energy Conversion,
Department of Mechanical
and Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: bosdas@lec.mavt.ethz.ch

Michel Mansour

Laboratory for Energy Conversion,
Department of Mechanical
and Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: michel.mansour@lec.mavt.ethz.ch

Anestis I. Kalfas

Department of Mechanical Engineering,
Aristotle University of Thessaloniki,
Thessaloniki 54124, Greece
e-mail: akalfas@auth.gr

Reza S. Abhari

Laboratory for Energy Conversion,
Department of Mechanical
and Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: rabhari@lec.mavt.ethz.ch

Shigeki Senoo

Mitsubishi Hitachi Power Systems, Ltd.,
3-1-1, Saiwai,
Hitachi 317-0073, Ibaraki, Japan
e-mail: shigeki1_senoo@mhps.com

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 14, 2015; final manuscript received August 9, 2015; published online September 22, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(3), 032601 (Sep 22, 2015) (12 pages) Paper No: GTP-15-1295; doi: 10.1115/1.4031345 History: Received July 14, 2015; Revised August 09, 2015

Modern steam turbines need to operate efficiently and safely over a wide range of operating conditions. This paper presents a unique unprecedented set of time-resolved steam flowfield measurements from the exit of the last two stages of a low pressure (LP) steam turbine under various volumetric massflow conditions. The measurements were performed in the steam turbine test facility in Hitachi city in Japan. A newly developed fast response probe equipped with a heated tip to operate in wet steam flows was used. The probe tip is heated through an active control system using a miniature high-power cartridge heater developed in-house. Three different operating points (OPs), including two reduced massflow conditions, are compared and a detailed analysis of the unsteady flow structures under various blade loads and wetness mass fractions is presented. The measurements show that at the exit of the second to last stage the flow field is highly three dimensional. The measurements also show that the secondary flow structures at the tip region (shroud leakage and tip passage vortices) are the predominant sources of unsteadiness at 85% span. The high massflow operating condition exhibits the highest level of periodical total pressure fluctuation compared to the reduced massflow conditions at the inlet of the last stage. In contrast at the exit of the last stage, the reduced massflow operating condition exhibits the largest aerodynamic losses near the tip. This is due to the onset of the ventilation process at the exit of the LP steam turbine. This phenomenon results in three times larger levels of relative total pressure unsteadiness at 93% span, compared to the high massflow condition. This implies that at low volumetric flow conditions the blades will be subjected to higher dynamic load fluctuations at the tip region.

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Figures

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Fig. 1

T–S diagram with steam turbine operating cycle and the respective probe tip operating temperature

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Fig. 2

FRAP-HT heated probe schematic and temperature measurement locations

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Fig. 3

Measurement concept in virtual six-hole mode with two-hole probe

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Fig. 4

FRAP-HTH extended calibration section's schematic for Ma = 0.3

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Fig. 5

LP steam turbine test facility where FRAP-HTH measurements were conducted

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Fig. 6

Schematic of the steam turbine test facility with the respective probe measurement locations

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Fig. 7

Relative flow yaw angle (a) and absolute Mach number (b) measured by the 5HP and FRAP-HTH probes at rotor exit of L-1 stage

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Fig. 8

Relative flow yaw angle (a) and absolute Mach number (b) of 5HP and FRAP-HTH probes at rotor exit of L-0 stage

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Fig. 9

(a) Time-averaged spanwise distribution of Cptrel and (b) time-averaged RMS of P′tot (Pa) at rotor exit of L-1 stage for OP-3, OP-2 and OP-1 with their respective minimum and maximum values obtained from the time-resolved data

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Fig. 10

Time-resolved Cptrel (—) at rotor exit of L-1 stage for OP-3

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Fig. 11

Time-resolved RMS of P′tot (Pa) in stationary frame of reference at rotor exit of L-1 stage for (a) OP-3 and (b) OP-1

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Fig. 12

Time-resolved relative yaw flow angle (deg) at rotor exit of L-1 stage for (a) OP-3 and (b) OP-1 (relative to blade metal angle)

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Fig. 13

Unsteady relative flow yaw and pitch angles, relative total and static pressure coefficients at 86% span for OP-3 and OP-1

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Fig. 14

Time-averaged spanwise distribution of the Cpt in relative frame of reference for two operating conditions (a) and difference in Cptrel between OP-2 with OP-3 (b)

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Fig. 15

Time-averaged spanwise distribution of Cptrel (a) and time-averaged P′tot RMS (Pa) (b) at rotor exit of L-0 stage for OP-2 and OP-3 with their respective minimum and maximum values obtained from the time-resolved data

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Fig. 16

Time-averaged spanwise distribution of Vradial/Vaxial at exit of L-0 stage

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Fig. 17

Time-resolved RMS of P′tot (Pa) in stationary frame of reference at rotor exit of L-0 stage for (a) OP-3 and (b) OP-2

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Fig. 18

Time-resolved relative flow yaw angle (deg) at rotor exit of L-0 stage for (a) OP-3 and (b) OP-2 (relative to blade metal angle)

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Fig. 19

Time-resolved Cptrel (—) at rotor exit for (a) OP-3 and (b) OP-2

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