Research Papers: Gas Turbines: Turbomachinery

Numerical Characterization of Hot-Gas Ingestion Through Turbine Rim Seals

[+] Author and Article Information
Riccardo Da Soghe

Ergon Research s.r.l.,
Via Panciatichi 92,
Florence 50127, Italy
e-mail: riccardo.dasoghe@ergonresearch.it

Cosimo Bianchini

Ergon Research s.r.l.,
Via Panciatichi 92,
Florence 50127, Italy

Carl M. Sangan, James A. Scobie, Gary D. Lock

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2016; final manuscript received July 28, 2016; published online October 11, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(3), 032602 (Oct 11, 2016) (9 pages) Paper No: GTP-16-1282; doi: 10.1115/1.4034540 History: Received June 28, 2016; Revised July 28, 2016

This paper deals with a numerical study aimed at the characterization of hot-gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, computational fluid dynamics (CFD) steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: For a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations displays a distinct kink. It was found that the “kink phenomenon” can be ascribed to an overestimation of the egress spoiling effects due to turbulence modeling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

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Fig. 1

Variation of static pressure in a turbine annulus. Radially inward arrows indicate hot-gas ingress and radially outward ones cooler egress, corresponding, respectively, to regions of higher and lower pressure than the wheel-space

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Fig. 2

Simplified diagram of ingress and egress, showing boundary layers on the stator and rotor

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Fig. 3

Rig test section (flow is from left to right)

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Fig. 5

Numerical grid details

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Fig. 6

Variation of effectiveness with nondimensional sealing flow rate for radial-clearance seal (colored symbols are computations, open symbols are experimental measurements made on the stator, and lines are theoretical curves from Eqs. (4) and (5))

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Fig. 7

Effect of sealing flow rate on radial variation of effectiveness on the stator for the radial-clearance seal: computations (left) and measurements (right)

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Fig. 8

Computed radial variation of effectiveness on stator and rotor surfaces for radial-clearance seal

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Fig. 9

Variation of effectiveness with nondimensional sealing flow rate for axial-clearance seal (colored symbols are computations, and open symbols are experimental measurements)

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Fig. 10

Distribution of Cp over nondimensional vane pitch and ΔCp0.5 for different Φ0 values (colored symbols are computations, and open symbols are experimental measurements)

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Fig. 11

Velocity contour across the rim: Φ0 = 0 (up) and Φ0 = 0.253 (down)

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Fig. 12

Sealing air concentration at low span, Φ0 = 0.253




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