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Review Article

Review of Ingress in Gas Turbines

[+] 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

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 Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 14, 2015; final manuscript received June 2, 2016; published online July 27, 2016. Assoc. Editor: Alexandrina Untaroiu.

J. Eng. Gas Turbines Power 138(12), 120801 (Jul 27, 2016) (16 pages) Paper No: GTP-15-1491; doi: 10.1115/1.4033938 History: Received October 14, 2015; Revised June 02, 2016

This review summarizes research concerned with the ingress of hot mainstream gas through the rim seals of gas turbines. It includes experimental, theoretical, and computational studies conducted by many institutions, and the ingress is classified as externally induced (EI), rotationally induced (RI), and combined ingress (CI). Although EI ingress (which is caused by the circumferential distribution of pressure created by the vanes and blades in the turbine annulus) occurs in all turbines, RI and CI ingress can be important at off-design conditions and for the inner seal of a double-seal geometry. For all three types of ingress, the equations from a simple orifice model are shown to be useful for relating the sealing effectiveness (and therefore the amount of hot gas ingested into the wheel-space of a turbine) to the sealing flow rate. In this paper, experimental data obtained from different research groups have been transformed into a consistent format and reviewed using the orifice model equations. Most of the published results for sealing effectiveness have been made using concentration measurements of a tracer gas (usually CO2) on the surface of the stator, and—for a large number of tests with single and double seals—the measured distributions of effectiveness with sealing flow rate are shown to be consistent with those predicted by the model. Although the flow through the rim seal can be treated as inviscid, the flow inside the wheel-space is controlled by the boundary layers on the rotor and stator. Using boundary-layer theory and the similarity between the transfer of mass and energy, a theoretical model has been developed to relate the adiabatic effectiveness on the rotor to the sealing effectiveness of the rim seal. Concentration measurements on the stator and infrared (IR) measurements on the rotor have confirmed that, even when ingress occurs, the sealing flow will help to protect the rotor from the effect of hot-gas ingestion. Despite the improved understanding of the “ingress problem,” there are still many unanswered questions to be addressed.

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References

Figures

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Fig. 1

(a) Typical high-pressure gas-turbine stage and (b) detail of rim seal

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Fig. 2

Variation of static pressure in a turbine annulus

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Fig. 3

Typical rim seal configurations: (a) axial-clearance, (b) radial-clearance, (c) double radial-clearance, and (d) engine-representative double-clearance seal

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Fig. 4

Operating capabilities of selected ingestion test facilities

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Fig. 5

Simplified flow structure for system with superposed sealing flow and ingress. (Side plots show radial velocity and concentration profiles within the boundary layers.)

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Fig. 6

Orifice ring—Owen [7]

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Fig. 7

Axial-clearance seal experimental data of Graber et al. [19] without vanes and blades fitted using Eqs. (3.7) and (3.9); open symbols—εc, shaded symbols Φi,RImin,RI (CF = 0.005, Reϕ = 5.1 × 106, Gc = 0.0048)

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Fig. 8

Radial-clearance seal experimental data of Graber et al. [19] without vanes and blades fitted using Eqs. (3.7) and (3.9); open symbols—εc, shaded symbols Φi,RImin,RI (CF = 0.01, Reϕ = 2.6 × 106)

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Fig. 9

Axial-clearance seal experimental data conducted under RI conditions from Sangan et al. [10], fitted using Eqs. (3.7) and (3.9); open symbols—εc, shaded symbols Φi,RImin,RI (CF = 0, Gc = 0.0105)

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Fig. 10

Radial-clearance seal experimental data conducted under RI conditions from Sangan et al. [10], fitted using Eqs. (3.7) and (3.9); open symbols—εc, shaded symbols Φi,RImin,RI (CF = 0, Gc = 0.0105)

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Fig. 11

Experimental data from Green and Turner [25], each condition fitted using Eq. (3.12) (Reϕ = 1.5 × 106, Gc = 0.01)

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Fig. 12

Experimental data from Gentilhomme et al. [28] fitted using Eq. (3.12) (Gc = 0.013)

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Fig. 13

Effect of rotor blades on ingestion for (a) configuration 1 (Gc = 0.015) and (b) configuration 2 (Gc = 0.005), Bohn et al. [32]

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Fig. 14

Variation of Cw,min with Cp,max½, from Bohn and Wolf [33]

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Fig. 15

Contours of (a) static pressure and (b) hot gas (hg) concentration in the wheel-space at Φ0 = 0.015 from 360 deg CFD simulation, Jakoby et al. [35] (Reϕ = 2.4 × 106, CF = 0.46, Gc = 0.03)

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Fig. 16

Diagrammatic representation of wheel-space static pressure distribution, from Childs [4]

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Fig. 17

Radial distribution of effectiveness for an axial-clearance and radial-clearance seal, Bohn et al. [37] (Reϕ = 2.4 × 106, CF = 0.46, Gc = 0.03)

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Fig. 18

Experimental data of Johnson et al. [16] fitted using Eqs. (3.12) and (3.13); open symbols—εc, shaded symbols Φi,EImin,EI (Reϕ = 5.9 × 105, Gc = 0.046)

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Fig. 19

Radial distribution of effectiveness for three radial-clearance seal geometries at Φ0 = 0.011, Zhou et al. [40] (Reϕ = 5.9 × 105, CF = 0.78, Gc = 0.046)

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Fig. 20

Experimental data of Balasubramanian et al. [17] fitted using Eqs. (3.12) and (3.13); open symbols—εc, shaded symbols Φi,EImin,EI (Gc = 0.046)

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Fig. 21

Comparison between theoretical effectiveness curves (Eqs. (3.12) and (3.13)) and experimental data for axial-clearance seal, Sangan et al. [9]; open symbols—εc, shaded symbols Φi,EImin,EI (CF = 0.54, Gc = 0.0105)

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Fig. 22

Radial distribution of effectiveness for three seal geometries tested at a consistent sealant flow rate, Sangan et al. [46] (Reϕ = 8.2 × 105, CF = 0.54, Gc = 0.0105)

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Fig. 23

Radial distribution of swirl ratio for three seal geometries tested at a consistent sealant flow rate, Sangan et al. [47] (Reϕ = 8.2 × 105, CF = 0.54, Gc = 0.0105)

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Fig. 24

Radial distribution of pressure coefficient for three seal geometries tested at a consistent sealant flow rate, symbols denote measurements, lines denote Eq. (5.2), Sangan et al. [47] (Reϕ = 8.2 × 105, CF = 0.54, Gc = 0.0105)

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Fig. 25

Variation of pressure and concentration effectiveness with sealant flow rate for radial-clearance seal (symbols denote data; line is theoretical curve), Owen et al. [48] (CF = 0.54, Gc = 0.0105)

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Fig. 26

Variation of effectiveness with nondimensional sealing flow rate showing thermal buffering effect on rotor, Cho et al. [49] (Reϕ = 8.2 × 105, CF = 0.54, Gc = 0.0105)

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Fig. 27

Experimental data from Phadke and Owen [23] fitted using Eq. (3.16) (Gc = 0.01)

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Fig. 28

Experimental data from Khilnani and Bhavnani [51] fitted using Eq. (3.16) (Gc = 0.01)

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Fig. 29

Experimental data from Scobie et al. [53] fitted using Eq. (3.16) (Reϕ = 5.3 × 105, Gc = 0.0105)

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Fig. 30

Experimental data from Scobie et al. [53] replotted in the style of Bohn and Wolff [33] (Reϕ = 5.3 × 105, Gc = 0.0105)

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