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Research Papers: Gas Turbines: Turbomachinery

Numerical Model of Liquid Film Formation and Breakup in Last Stage of a Low-Pressure Steam Turbine

[+] Author and Article Information
Pietro Rossi

Laboratory of Energy Conversion,
Department of Mechanical and
Process Engineering,
ETH Zürich,
Zürich 8092, Switzerland
e-mail: pietro.rossi@alumni.ethz.ch

Asad Raheem

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

Reza S. Abhari

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

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 1, 2017; final manuscript received July 25, 2017; published online October 17, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(3), 032602 (Oct 17, 2017) (8 pages) Paper No: GTP-17-1189; doi: 10.1115/1.4037912 History: Received June 01, 2017; Revised July 25, 2017

Formation of thin liquid films on steam turbine airfoils, particularly in last stages of low-pressure (LP) steam turbines, and their breakup into coarse droplets is of paramount importance to assess erosion of last stage rotor blades given by the impact of those droplets. An approach for this problem is presented in this paper: this includes deposition of liquid water mass and momentum, film mass and momentum conservation, trailing edge breakup and droplets Lagrangian tracking accounting for inertia and drag. The use of thickness-averaged two-dimensional (2D) equations in local body-fitted coordinates, derived from Navier–Stokes equations, makes the approach suitable for arbitrary curved blades and integration with three-dimensional (3D) computational fluid dynamics (CFD) simulations. The model is implemented in the in-house solver MULTI3, which uses Reynolds-averaged Navier–Stokes equations κω model and steam tables for the steam phase and was previously modified to run on multi-GPU architecture. The method is applied to the last stage of a steam turbine in full and part load operating conditions to validate the model by comparison with time-averaged data from experiments conducted in the same conditions. Droplets impact pattern on rotor blades is also predicted and shown.

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References

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Figures

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Fig. 1

Comparison of model and experiments for flat plate film flow in steam turbine conditions

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Fig. 2

Computational subdomains of the turbine sector geometry

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Fig. 3

FRAP-HTH measurements location

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Fig. 4

Comparison of CFD and FRAP-HTH for OP-1: static to total pressure ratio (a) and flow yaw angle (b)

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Fig. 5

Comparison of CFD and FRAP-HTH for OP-2: static to total pressure ratio (a) and flow yaw angle (b)

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Fig. 6

Comparison of droplets model (a) and OB probe (b) for Sauter mean diameter d32

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Fig. 7

Film thickness (μm) for OP-2: PS (a) and SS (b)

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Fig. 8

Film total velocity (m/s) for OP-2: SS on the left and PS on the right

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Fig. 9

Erosion levels on L-0 rotor blade: PS (a) and SS (b)

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Fig. 10

Mass flow at trailing edge (a) and impacting mass on rotor blades (b)

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Fig. 11

Circumferentially integrated nondimensional erosion level

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