Research Papers

The Thermodynamics of Wake Blade Interaction in Axial Flow Turbines: Combined Experimental and Computational Study

[+] Author and Article Information
Martin Rose

Institut für Luftfahrtantriebe Stuttgart
University Stuttgart, Germany
e-mail: rose@ila.uni-stuttgart.de

Michel Mansour

Laboratory for Energy Conversion,
ETH Zürich, Switzerland

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 23, 2012; final manuscript received June 29, 2012; published online March 25, 2013. Editor: David Wisler.

J. Turbomach 135(3), 031015 (Mar 25, 2013) (10 pages) Paper No: TURBO-12-1076; doi: 10.1115/1.4007480 History: Received June 23, 2012; Revised June 29, 2012

This paper reports on insights into the detailed thermodynamics of axial turbine nozzle guide vane (NGV) wakes as they interact with the rotor blades. The evidence presented is both computational and experimental. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations are used to compare the experimental observations with theoretical predictions. Output processing with both Eulerian and Lagrangian approaches is used to track the property variation of the fluid particles. The wake is found to be hot and loses heat to the surrounding fluid. The Lagrangian output processing shows that the entropy of the wake will fall due to heat loss as it passes through the rotor and this is corroborated experimentally. The experimental vehicle is a 1.5-stage shroudless turbine with modest Mach numbers of 0.5 and high response instrumentation. The entropy reduction of the wake is determined to be about four times the average entropy rise of the whole flow across the rotor. The results show that the work done by the wake fluid on the rotor is approximately 24% lower than that of the free-stream. The apparent experimental efficiency of the wake fluid is 114% but the overall efficiency of the turbine at midheight is around 95%. It is concluded that intrafluid heat transfer has a strong impact on the loss distribution even in a nominally adiabatic turbine with moderate row exit Mach numbers of 0.5.

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Fig. 2

2D URANS results: (a) instantaneous entropy, (b) unsteady work at the same time instant, and (c) absolute frame time average of the unsteady work

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Fig. 1

Computational grid used for the 2D unsteady CFD stage calculation

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Fig. 3

Particle paths viewed in the relative frame starting at five points in the relative frame. Aerofoil shown at a point in time for reference.

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Fig. 4

Lagrangian output processing of URANS solution: variation of static temperature versus axial coordinate

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Fig. 10

Picture of the midheight aerodynamic form of the LISA 1.5-stage shroudless research turbine

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Fig. 5

Euler work term Eq. (2) for fluid particles passing through the rotor

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Fig. 6

Isentropic temperature difference for particles of fluid passing through a rotor

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Fig. 7

(a) Plot of total temperature against change in entropy (Δs/Cv) for particle paths in rotor. (b) Interpretation of (a) into the processes of heat transfer, work, and mixing.

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Fig. 8

Fast response aerodynamic probe (FRAP)

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Fig. 11

Conceptual unsteady control volume used to analyze the experimental results

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Fig. 12

Space time diagram of FRAP probe total pressure at midheight and NGV exit S1ex

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Fig. 13

Space-time diagram of FRAP data at midheight and rotor exit R1ex: rms of the total pressure in Pa

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Fig. 14

rms total pressure versus time at R1ex TR8 midheight

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Fig. 15

Graph of Lagrangian output processing for particles passing through the rotor; entropy (Δs/Cv) versus total temperature. Symbols are experimental data (see key).

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Fig. 16

This figure shows the results of Lagrangian output processing for particles passing through the rotor. The variable plotted is the axial velocity u in m/s.



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