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Research Papers: Gas Turbines: Structures and Dynamics

# Unsteady Flow Phenomena in Turbine Rim Seals

[+] Author and Article Information
Paul F. Beard

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: paul.beard@eng.ox.ac.uk

Feng Gao, John Chew

Faculty of Engineering and Physical Sciences,
University of Surrey,
Guildford GU2 7XH, UK
e-mail: f.gao@surrey.ac.uk

Kam S. Chana

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: kam.chana@eng.ox.ac.uk

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 6, 2016; final manuscript received July 8, 2016; published online September 27, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(3), 032501 (Sep 27, 2016) (10 pages) Paper No: GTP-16-1312; doi: 10.1115/1.4034452 History: Received July 06, 2016; Revised July 08, 2016

## Abstract

While turbine rim sealing flows are an important aspect of turbomachinery design, affecting turbine aerodynamic performance and turbine disk temperatures, the present understanding and predictive capability for such flows is limited. The aim of the present study is to clarify the flow physics involved in rim sealing flows and to provide high-quality experimental data for use in evaluation of computational fluid dynamics (CFD) models. The seal considered is similar to a chute seal previously investigated by other workers, and the study focuses on the inherent unsteadiness of rim seal flows, rather than unsteadiness imposed by the rotating blades. Unsteady pressure measurements from radially and circumferentially distributed transducers are presented for flow in a rotor–stator disk cavity and the rim seal without imposed external flow. The test matrix covered ranges in rotational Reynolds number, $Re∅$, and nondimensional flow rate, $Cw$, of 2.2–3.0 × 106 and 0–3.5 × 103, respectively. Distinct frequencies are identified in the cavity flow, and detailed analysis of the pressure data associates these with large-scale flow structures rotating about the axis. This confirms the occurrence of such structures as predicted in previously published CFD studies and provides new data for detailed assessment of CFD models.

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## Figures

Fig. 1

Schematic of the Oxford Rotor Facility

Fig. 2

(a) Drawing of ORF working section and (b) rim seal geometry (dimensions in mm)

Fig. 3

Feed distributor with instrumentation

Fig. 4

Schematic of unsteady pressure sensors instrumentation on vane platform ring (viewed from downstream)

Fig. 5

Unsteady pressure sensors mounted in vane platform

Fig. 6

Radial growth of rotor assembly against rotational speed

Fig. 7

Radial data of mean pressure relative to tapping 1 for all tests with Cw=0. Results at r/b = 1.01 represent external (atm) pressure.

Fig. 8

Variation of mean pressure at tapping 4 (r/b=0.988) relative to external tapping with cavity flow rate for the two seal gaps

Fig. 9

Comparison of raw and filtered unsteady pressure data at position 1001: top—raw data, middle—ensemble average for 150 revs, and bottom—frequency spectra. Ω = 9000 rpm, sc=1  mm, and m=3.55 g/s (Reφ=2.8×106 and  Cw=740).

Fig. 10

FFT of unsteady pressure data from radial tappings; sc=1 mm, m=11.5 g/s,  Re∅=0−3×106,  and Cw=2.5×103

Fig. 11

FFT of unsteady pressure data from radial tappings; sc=1 mm, Ω=9000 rpm, Re∅=3×106,  and Cw=0−3.4×103 (circles show peak f/Ω and p/0.5ρΩ2b2 plotted in subsequent figures)

Fig. 12

Comparison of ppeak/0.5ρΩ2b2 versus um/Ωb for all sensor locations and both seal gap sizes: sc=1 mm (left); sc=1.65 mm (right); Re∅=2.2−3×106 and  Cw=0−3.4×103

Fig. 13

Comparison of peak f/Ω versus um/Ωb for all sensor locations and both seal gap sizes: sc=1 mm (left); sc=1.65 mm (right); Re∅=2.2−3×106 and Cw=0−3.4×103

Fig. 14

Illustration of cavity flow structure

Fig. 15

Filtered unsteady data for the six circumferentially spaced sensors: sc=1 mm, m=11.5 g/s, and Ω=9000 rpm (Re∅=2.9×106 and Cw=2.5×103)

Fig. 16

Results of cross-correlation over one revolution of sensors 1007 and 1008: sc=1 mm, m=11.5 g/s, and Ω=9000 rpm (Re∅=2.9×106 and  Cw=2.5×103)

Fig. 17

Histogram of normalized lag time from analysis of 150 revolutions for sensors 1007 and 1008: sc=1 mm, m=11.5 g/s, and Ω=9000 rpm

Fig. 18

Summary plots for cross-correlation of all sensor pairs for sc=1 mm and Ω=9000 rpm:  m=0  g/s (bottom), m=11.5 g/s (middle), and m=15.5 g/s (top); Re∅=2.7−3.0×106 and  Cw=0−3.4×103

Fig. 19

Summary plots for cross-correlation of all sensor pairs for sc=1 mm and Ω=7000 rpm:  m=0 g/s (bottom), m=11.5  g/s (middle), and m=15.5 g/s (top); Re∅=2.2−2.5×106 and Cw=0−3.5×103

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