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research-article

Experimental and Computational Investigation of Flow Instabilities in Turbine Rim Seals

[+] Author and Article Information
Josh Horwood

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom
j.t.m.horwood@bath.ac.uk

Fabian Hualca

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom
f.hualca@bath.ac.uk

James Scobie

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom
j.a.scobie@bath.ac.uk

Mike Wilson

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom
m.wilson@bath.ac.uk

Carl Sangan

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom
c.m.sangan@bath.ac.uk

Gary Lock

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom
g.d.lock@bath.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4041115 History: Received July 02, 2018; Revised July 17, 2018

Abstract

In high-pressure turbines, cool air is purged through rim seals at the periphery of wheel-spaces between the stator and rotor discs. 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 disc 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 disc speed. It is hypothesised 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 under-prediction by the computations of the measured levels of ingress is caused by deficiencies in the turbulence modelling.

Copyright (c) 2018 by ASME
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