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Research Papers: Gas Turbines: Turbomachinery

Measurements and Modeling of Ingress in a New 1.5-Stage Turbine Research Facility

[+] Author and Article Information
Marios Patinios

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

James A. Scobie

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

J. Michael Owen

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: j.m.owen@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 Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 29, 2016; final manuscript received June 30, 2016; published online August 23, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(1), 012603 (Aug 23, 2016) (12 pages) Paper No: GTP-16-1291; doi: 10.1115/1.4034240 History: Received June 29, 2016; Revised June 30, 2016

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor disks as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance, and integrity of highly stressed, vulnerable engine components. Rim seals, fitted at the periphery of the disks, are used to minimize ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the disks. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. The fluid-dynamically scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure, and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Typical rim seal in a high-pressure turbine

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Fig. 4

Flow structure expected in the downstream wheel-space

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Fig. 5

Operating conditions of ingress test facilities

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Fig. 6

Effect of sealing flow rate on radial distribution of effectiveness in the downstream wheel-space (data adapted from Ref. [16]: Reϕ = 5.3 × 105, CF = 1.02, Gc = 0.031)

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Fig. 3

Simplified diagram of ingress and egress in the upstream wheel-space, showing concentration and velocity boundary layers on the stator and rotor surfaces

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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 (see online version for color).

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Fig. 7

Variation of effectiveness with nondimensional sealing flow rate at r/b = 0.85 and 0.68 fitted using Eq. (2.6) (data adapted from Ref. [16]: Reϕ = 5.3 × 105, CF = 1.02, Gc = 0.031)

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Fig. 8

Exploded view of 1.5-stage experimental facility

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Fig. 9

Test section and instrumentation for the turbine rig

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Fig. 10

Effect of Reϕ on circumferential distribution of Cp,a in annulus over nondimensional vane pitch at two axial locations (A1: white symbols; A2: gray symbols) CF = 0.34

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Fig. 11

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

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Fig. 12

Circumferential variation of concentration effectiveness with nondimensional vane pitch in the upstream wheel-space at three radial locations (Reϕ = 7.2 × 105, CF = 0.34, and Φ0 = 0.012)

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Fig. 13

Effect of sealing flow rate on radial distribution of effectiveness in the upstream wheel-space (Reϕ = 7.20 × 105 and CF = 0.34) (circles: stator wall; diamonds: rotating core)

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Fig. 14

Effect of sealing flow rate on radial distribution of effectiveness in the downstream wheel-space (Reϕ = 7.2 × 105 and CF = 0.34) (circles: stator wall; diamonds: rotating core)

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Fig. 15

Variation of εc with Φ0 at r/b = 0.958 and 0.85 in the upstream and the downstream wheel-spaces for CF = 0.34 (symbols denote data; lines are theoretical curves from Eq. (2.6))

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Fig. 16

Effect of sealing flow rate on distribution of swirl ratio and pressure coefficient in the upstream wheel-space (symbols: measured values; dash lines: calculated distribution for Cp)

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Fig. 17

Effect of sealing flow rate on distribution of swirl ratio and pressure coefficient in the downstream wheel-space (symbols: measured values; dash lines: calculated distribution for Cp)

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