Research Papers

Unsteady Interaction Between Annulus and Turbine Rim Seal Flows

[+] Author and Article Information
Martin Chilla

e-mail: mc618@cam.ac.uk

Howard Hodson

Whittle Laboratory,
University of Cambridge,
Cambridge, UK

David Newman

Rolls-Royce plc,
Derby, UK

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 18, 2012; final manuscript received October 19, 2012; published online June 28, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051024 (Jun 28, 2013) (10 pages) Paper No: TURBO-12-1193; doi: 10.1115/1.4023016 History: Received September 18, 2012; Revised October 19, 2012

In core gas turbines relatively cold air is purged through the hub gap between the stator and rotor in order to seal the disk space against flow ingestion from the main annulus. Although the sealing mass flow rate is commonly very small compared to the main annulus mass flow rate, it can have significant effects on the development of the passage endwall flows and on the overall loss generation. In this paper, the interaction between the annulus and rim sealing flows is investigated using numerical simulations of a generic high-pressure turbine. At first, the numerical approach is validated by comparing the results of calculations to measurement data at the design flow conditions. Following that, results from steady and unsteady calculations are used to describe in detail the aerodynamics in overlap-type rim seals and their effects on the blade passage flow. It is found that the flow interaction at the rim seal interface is strongly influenced by the velocity deficit of the rim sealing flow relative to the annulus flow as well as by the circumferentially nonuniform pressure field imposed by the rotor blades. At typical sealing flow conditions, the flow interaction at the rim seal interface is found to be naturally unsteady, with periodical vortex shedding into the rotor passage. The rim seal geometry, in particular close to the annulus interface, is found to have an effect on the frequency of the shedding process. Finally, it is shown that the rim seal flow interaction can be stabilized by increasing either the sealing mass flow rate or the sealing tangential velocity.

Copyright © 2013 by ASME
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Fig. 1

The Rolls-Royce generic turbine rig

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Fig. 2

Numerical model configurations of the generic turbine rig

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Fig. 3

Details of rotor zone mesh

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Fig. 4

Comparison of whirl angle and total pressure profiles between model configuration (b) and rig measurement data

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Fig. 5

Schematic of global annulus and rim sealing flow velocity triangles at rim seal interface

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Fig. 6

Relative frame streamline-projections into axial cut-plane at rim seal interface, colored by static temperature; snapshot solution of configuration (d)

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Fig. 7

Relative frame time-averaged contours of radial velocity at rim seal interface of configuration (c)

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Fig. 8

Relative frame time-averaged streamline-projections into meridional plane colored by static temperature (configuration (c))

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Fig. 9

Unsteady static pressure signals from local monitors rotating with blades; left—midspan, right—rim seal interface (configuration (a))

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Fig. 10

Frequency spectra corresponding to static pressure signals in Fig. 9

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Fig. 11

Instantaneous contours of relative frame circumferential vorticity over rim seal shedding cycle (configuration (c))

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Fig. 12

Unsteady blade loading at 2% and 50% blade height (configuration (c))

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Fig. 13

Instantaneous relative total pressure contours downstream of blade passage over rim seal shedding cycle (configuration (c))

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Fig. 14

Time-averaged contours of absolute tangential velocity for four different rim seal shapes (configuration (c))

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Fig. 15

Variation of relative frame pressure frequency spectrum with rim seal shape (configuration (c))

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Fig. 16

Effect of sealing mass flow rate and tangential velocity (a) on mean performance and (b) on performance standard deviation (configuration (b))

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Fig. 17

Contours of adiabatic surface temperature and meridional streamline-projections for different rim seal inflow conditions (configurations (b) and (c))




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