Research Papers

Experimental and Computational Investigation of Flow Instabilities in Turbine Rim Seals

[+] Author and Article Information
Joshua T. M. Horwood

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

Fabian P. Hualca

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

Michael Wilson

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: m.wilson@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

Manuscript received July 2, 2018; final manuscript received July 17, 2018; published online October 17, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(1), 011028 (Oct 17, 2018) (12 pages) Paper No: GTP-18-1415; doi: 10.1115/1.4041115 History: Received July 02, 2018; Revised July 17, 2018

In high-pressure turbines, cool air is purged through rim seals at the periphery of wheel-spaces between the stator and rotor disks. The purge suppresses the ingress of hot gas from the annulus but superfluous use is inefficient. In this paper, the interaction between the ingress, purge, and mainstream flow is studied through comparisons of newly acquired experimental results alongside unsteady numerical simulations based on the DLR TRACE solver. New experimental measurements were taken from a one-and-a-half stage axial-turbine rig operating with engine-representative blade and vane geometries, and overlapping rim seals. Radial traverses using a miniature CO2 concentration probe quantified the penetration of ingress into the rim seal and the outer portion of the wheel-space. Unsteady pressure measurements from circumferentially positioned transducers on the stator disk identified distinct frequencies in the wheel-space, and the computations reveal these are associated with large-scale flow structures near the outer periphery rotating at just less than the disk speed. It is hypothesized that the physical origin of such phenomenon is driven by Kelvin–Helmholtz instabilities caused by the tangential shear between the annulus and egress flows, as also postulated by previous authors. The presence and intensity of these rotating structures are strongly dependent on the purge flow rate. While there is general qualitative agreement between experiment and computation, it is speculated that the underprediction by the computations of the measured levels of ingress is caused by deficiencies in the turbulence modeling.

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Fig. 1

Comparison of rotating low-pressure structures from literature

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Fig. 2

The bath 1.5 stage turbine facility: test section and instrumentation

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Fig. 4

Computational domain

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Fig. 5

Circumferential distribution of pressure coefficient in annulus over two nondimensional vane pitches (Φ0 = 0.029, Reϕ = 1.0 × 106)

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Fig. 6

Contours of concentration-based effectiveness through the annulus (clipped to > 3%), with stream-traces originating from the seal (Φ0 = 0.104, Reϕ = 1.0 × 106)

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Fig. 7

Concentration-based sealing effectiveness through the annulus for Φ0 = 0.104, Reϕ=1.0×106: isosurface of 5% effectiveness (left), radial traverses of effectiveness upstream and downstream of the blade (right)

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Fig. 8

Concentration-based sealing effectiveness through the seal at Reϕ=1.0×106: radial traverse measurements into the seal (left), contours of computational distribution at Φ0 = 0.021 (right)

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Fig. 9

Concentration-based sealing effectiveness in the wheel-space at Reϕ=1.0×106: (a) Φ0 = 0.021 and (b) Φ0 = 0.029

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Fig. 10

Variation in wheel-space concentration effectiveness with nondimensional sealing parameter

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Fig. 11

Variation in swirl at Reϕ=1.0×106

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Fig. 12

Fast Fourier transforms of unsteady computational data at r/b = 0.993 and Reϕ=1.0×106

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Fig. 13

Fast Fourier transforms of unsteady computational data at four locations through the seal: Φ0 = 0.021; Reϕ = 1.0×106

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Fig. 14

The formation of Kelvin Helmholtz instabilities

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Fig. 15

Instantaneous contours of effectiveness through the rim seal with streamlines taken in the rotational frame and with the stator hidden: (a) Φ0 = 0.021 and (b) Φ0 = 0.104

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Fig. 16

Fast Fourier transforms of unsteady experimental data at r/b = 0.993 on the wheel-space stator wall



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