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Research Papers: Research Papers

Influence of Leakage Flows on Hot Gas Ingress

[+] Author and Article Information
Marios Patinios

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

Irvin L. Ong

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: Irvin.l.ong@bath.edu

James A. Scobie

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

Carl M. Sangan

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

Manuscript received June 29, 2018; final manuscript received July 3, 2018; published online September 26, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(2), 021010 (Sep 26, 2018) (10 pages) Paper No: GTP-18-1403; doi: 10.1115/1.4040846 History: Received June 29, 2018; Revised July 03, 2018

One of the most important problems facing gas turbine designers today is the ingestion of hot mainstream gases into the wheel-space between the turbine disk (rotor) and its adjacent casing (stator). A rim seal is fitted at the periphery and a superposed sealant flow—typically fed through the bore of the stator—is used to prevent ingress. The majority of research studies investigating ingress do so in the absence of any leakage paths that exist throughout the engine's architecture. These inevitable pathways are found between the mating interfaces of adjacent pieces of hardware. In an environment where the turbine is subjected to aggressive thermal and centrifugal loading, these interface gaps can be difficult to predict and the resulting leakage flows which pass through them even harder to account for. This paper describes experimental results from a research facility which experimentally models hot gas ingestion into the wheel-space of an axial turbine stage. The facility was specifically designed to incorporate leakage flows through the stator disk; leakage flows were introduced axially through the stator shroud or directly underneath the vane carrier ring. Measurements of CO2 gas concentration, static pressure, and total pressure were used to examine the wheel-space flow structure with and without ingress from the mainstream gas-path. Data are presented for a simple axial-clearance rim-seal. The results support two distinct flow-structures, which are shown to be dependent on the mass-flow ratio of bore and leakage flows. Once the leakage flow was increased above a certain threshold, the flow structure is shown to transition from a classical Batchelor-type rotor-stator system to a vortex-dominated structure. The existence of a toroidal vortex immediately inboard of the outer rim-seal is shown to encourage ingestion.

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References

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Figures

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Fig. 3

Test section and instrumentation of the 1-stage turbine rig

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Fig. 2

Interaction of purge and leakage flows in the rim seal region [5]

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Fig. 1

Sealing flow (main figure) and leakage flow (inset) paths in a typical turbine stage (adapted from Ref. [1])

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Fig. 5

Representation of control volume for the case of (a) no ingress and cB > cL and (b) with ingress and cB = cL

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Fig. 7

Simplified flow structures expected for a rotor-stator system with ingress, superposed sealing flow (m˙B) and leakage flow at high radius (m˙L): (a) m˙L<m˙B and (b) m˙L≥m˙B

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Fig. 4

Axial seal configuration in the turbine wheel-space

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Fig. 6

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

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Fig. 10

Effect of sealing flow rate on radial distribution of pressure coefficient for the following cases: (a) bore flow only, (b) combined supply, and (c) leakage flow only—symbols: experimental measurements; lines: calculated distribution of Cp

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Fig. 8

Effect of Rm˙ on radial distribution of C* (left) and Cp(right): (a) Rm˙ < 1 and (b) Rm˙ ≥ 1 (circles—stator wall; diamonds-rotating core) (Φ0 = 0.25)

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Fig. 9

Circumferential variation of concentration effectiveness for the following cases: bore flow only, leakage flow only, and a combined supply; in all cases, Φ0 = 0.127. (r/b = 0.85 (shaded symbols) and r/b = 0.958 (open symbols)).

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Fig. 13

Variation of εc with Φ0 at r/b = 0.847 for the bore flow only, leakage flow only, and three combined supply cases

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Fig. 11

Effect of sealing flow rate on radial distribution of effectiveness for the bore flow only case—circles: stator wall; diamonds: measurements at z/S = 0.3125

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Fig. 12

Effect of sealing supply arrangement on radial distribution of |Δεc|

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Fig. 14

Effect of leakage flow supply radius on the variation of εc with Φ0 (data measured at r/b = 0.847)

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