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Research Papers: Gas Turbines: Structures and Dynamics

Egress Interaction Through Turbine Rim Seals

[+] Author and Article Information
James A. Scobie

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: j.a.scobie@bath.ac.uk

Fabian P. Hualca

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: f.hualca@bath.ac.uk

Carl M. Sangan

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: c.m.sangan@bath.ac.uk

Gary D. Lock

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: g.d.lock@bath.ac.uk

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 10, 2017; final manuscript received September 4, 2017; published online April 10, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(7), 072504 (Apr 10, 2018) (9 pages) Paper No: GTP-17-1332; doi: 10.1115/1.4038458 History: Received July 10, 2017; Revised September 04, 2017

Engine designers require accurate predictions of ingestion (or ingress) principally caused by circumferential pressure asymmetry in the mainstream annulus. Cooling air systems provide purge flow designed to limit metal temperatures and protect vulnerable components from the hot gases which would otherwise be entrained into disk cavities through clearances between rotating and static disks. Rim seals are fitted at the periphery of these disks to minimize purge. The mixing between the efflux of purge (or egress) and the mainstream gases near the hub end-wall results in a deterioration of aerodynamic performance. This paper presents experimental results using a turbine test rig with wheel-spaces upstream and downstream of a rotor disk. Ingress and egress was quantified using a CO2 concentration probe, with seeding injected into the upstream and downstream sealing flows. The probe measurements have identified an outer region in the wheel-space and confirmed the expected flow structure. For the first time, asymmetric variations of concentration have been shown to penetrate through the seal clearance and the outer portion of the wheel-space between the disks. For a given flow coefficient in the annulus, the concentration profiles were invariant with rotational Reynolds number. The measurements also reveal that the egress provides a film-cooling benefit on the vane and rotor platforms. Further, these measurements provide unprecedented insight into the flow interaction and provide quantitative data for computational fluid dynamics (CFD) validation, which should help to reduce the use of purge and improve engine efficiency.

Copyright © 2018 by ASME
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References

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Figures

Grahic Jump Location
Fig. 1

Typical rim seal in a high-pressure turbine

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Fig. 2

Variation of static pressure in a turbine annulus highlighting regions of ingress and egress. Red indicates upstream of rotor disk, and blue indicates downstream [2].

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Fig. 3

Flow structure in upstream and downstream wheel-spaces

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Fig. 4

Experimental facility—for clarity, some inlet pipes and the annulus casing have been removed

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Fig. 5

Axial- and radial-clearance seal configuration in the upstream and downstream wheel-spaces

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Fig. 6

(a) Location of upstream (A1) and downstream (A3) circumferential pressure taps on stator-vane platforms and (b) circumferential distribution of steady pressure coefficient in annulus over two nondimensional vane pitches 180 deg apart (open symbols location A1 upstream of rotor; gray symbols location A3 downstream of rotor)

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Fig. 7

Test section and instrumentation

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Fig. 8

Radial variation of effectiveness measured using the concentration probe showing Reϕ independence

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Fig. 9

Effect of sealing flow rate on radial distribution of effectiveness in the downstream wheel-space (Reϕ = 7.20 × 105 and CF = 0.29) (squares: stator-wall; diamonds: rotating-core; circles: probe measurements)

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Fig. 10

Variation of concentration effectiveness, ingress, and egress flow ratios with nondimensional sealing flow rate in the downstream wheel-space (symbols denote data; lines are theoretical orifice-model fits)

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Fig. 11

Radial traverse through upstream axial-clearance rim seal for four circumferential positions relative to upstream vane (Φ0,u = Φmin,u)

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Fig. 12

Radial traverse through downstream axial-clearance rim seal for four circumferential positions relative to downstream vane (Φ0,d = Φmin,d)

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Fig. 13

Comparison of axial- and radial-clearance rim seals in upstream wheel-space (θ = 0.189)

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Fig. 14

Comparison of axial- and radial-clearance rim seals in downstream wheel-space (θ = 0.311)

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Fig. 15

Radial traverse of egress downstream of the seal clearance (Φ0,d =Φmin,dR and θ = 0.42)

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Fig. 16

Variation of concentration effectiveness and pressure coefficient with nondimensional vane pitch—location A3

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