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Research Papers: Gas Turbines: Structures and Dynamics

Theoretical Model to Determine Effect of Ingress on Turbine Disks

[+] Author and Article Information
L. Isobel Mear

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: isobel.mear@gmail.com

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

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 13, 2015; final manuscript received July 28, 2015; published online September 22, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(3), 032502 (Sep 22, 2015) (9 pages) Paper No: GTP-15-1259; doi: 10.1115/1.4031315 History: Received July 13, 2015; Revised July 28, 2015

Sealing air is used in gas turbines to reduce the amount of hot gas that is ingested through the rim seals into the wheel-space between the turbine disk and its adjacent stationary casing. The sealing air attaches itself to the rotor, creating a buffering effect that reduces the amount of ingested fluid that can reach the surface of the rotor. In this paper, a theoretical model is developed, and this shows that the maximum buffering effect occurs at a critical flow rate of sealing air, the value of which depends on the seal geometry. The model, which requires two empirical constants, is validated using experimental data, obtained from infrared (IR) temperature measurements, which are presented in a separate paper. There is good agreement between the adiabatic effectiveness of the rotor estimated from the model and that obtained from the IR measurements. Of particular interest to designers is that significant ingress can enter the wheel-space before its effect is sensed by the rotor.

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References

Figures

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Fig. 1

Generic rotor–stator turbine stage and double seal inset

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Fig. 2

Simplified flow structure for a rotor–stator system with superposed sealing flow and ingress

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Fig. 3

Simplified representation of buffering effect: (a) λT = 0; (b) λT < λT,min; and (c) λT = λT,min

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Fig. 4

Buffer ratio and buffer effect for single seals. Symbols denote experimental data and curves are determined from theoretical models. (a) Axial-clearance seal and (b) radial-clearance seal.

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Fig. 5

Buffer ratio and buffer effect for double seals. Symbols denote experimental data and curves are determined from theoretical models. Solid and dashed lines denote outer and inner cavity measurements, respectively. (a) Axial-clearance seal and (b) radial-clearance seal.

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Fig. 6

Tested rim seal geometries

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Fig. 7

Variation of effectiveness with sealing flow rate for single seals. Symbols denote experimental data, and curves are determined from theoretical models. (a) Axial-clearance seal and (b) radial-clearance seal.

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Fig. 8

Variation of effectiveness with sealing flow rate for double axial-clearance seal. Symbols denote experimental data, and curves are determined from theoretical models. (a) Inner wheel-space and (b) outer wheel-space.

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Fig. 9

Variation of effectiveness with sealing flow rate for double radial-clearance seal. Symbols denote experimental data, and curves are determined from theoretical models. (a) Inner wheel-space and (b) outer wheel-space.

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Fig. 10

Axial-clearance seal configurations: (a) Pountney et al. [2] and (b) Cho et al. [1]

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Fig. 11

Buffer ratio and buffer effect for single axial-clearance seal of Pountney et al. [2]. Symbols denote experimental data, and curves are determined from theoretical models.

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Fig. 12

Variation of effectiveness with sealing flow rate for single axial-clearance seal of Pountney et al. [2]. Symbols denote experimental data, and curves are determined from theoretical models.

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