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Research Papers

Effects of an Upstream Cavity on the Secondary Flow in a Transonic Turbine Cascade

[+] Author and Article Information
H. M. Abo El Ella

S. A. Sjolander

Mechanical and Aerospace Engineering,  Carleton University, Ottawa, Ontario, ON K1S 5B6, Canadassjoland@mae.carleton.ca

T. J. Praisner

Pratt and Whitney Aircraft,  United Technologies, East Hartford, Connecticut, 06108thomas.praisner@pw.utc.com

J. Turbomach 134(5), 051009 (May 08, 2012) (9 pages) doi:10.1115/1.4003818 History: Received December 01, 2010; Revised February 02, 2011; Published May 08, 2012; Online May 08, 2012

This paper examines experimentally the effects of an upstream cavity on the flow structures and secondary losses in a transonic linear turbine cascade. The cavity approximates the endwall geometry resulting from the platform overlap at the interface between stationary and rotating turbine blade rows. Previous investigations of the effects of upstream cavity geometries have been conducted mainly at low-speed conditions. The present work aims to extend such research into the transonic regime with a more engine representative upstream platform geometry. The investigations were carried out in a blow-down type wind tunnel. The cavity is located at 30 % of axial chord from the leading edge, extends 17 % of axial-chord in depth, and is followed by a smooth ramp to return the endwall to its nominal height. Two cascades are examined for the same blade geometry: the baseline cascade with a flat endwall and the cascade with the cavity endwall. Measurements were made at the design incidence and the outlet design Mach number of 0.80. At this condition, the Reynolds number based on outlet velocity is about 600,000. Off-design outlet Mach numbers of 0.69, and 0.89 were also investigated. Flowfield measurements were carried out at 40 % axial-chord downstream of the trailing edge, using a seven-hole pressure probe, to quantify losses and identify the flow structures. Additionally, surface flow visualization using an ultra-violet reactive dye was employed at the design Mach number, on the endwall and blade surfaces, to help in the interpretation of the flow physics. The experimental results also include blade-loading distributions, and the probe measurements were processed to obtain total-pressure loss coefficients, and streamwise vorticity distributions. It was found that the presence of the upstream cavity noticeably altered the structure and the strength of the secondary flow. Some effect on the secondary losses was also evident, with the cavity having a larger effect at the higher Mach number.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical modern engine cavity geometry - adapted from Ref. [1]

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Figure 2

Carleton University - Pratt & Whitney Canada high speed wind tunnel

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Figure 3

Upstream cavity geometry

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Figure 4

Measurement grid and location

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Figure 5

Inlet boundary layer traverse results

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Figure 10

Oil surface flow visualization at design mach number: (a) flat endwall surface, first view; (b) cavity endwall surface, first view; (c) flat endwall surface, second view; (d) cavity endwall surface, second view; (e) flat endwall suction surface; (f) cavity endwall suction surface

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Figure 11

Pitchwise mass averaged normalized losses

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Figure 12

Total mass averaged normalized losses

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Figure 9

Streamwise vorticity: (a) flat endwall below design, M2 0.69; (b) cavity endwall below, design M2 0.69; (c) flat endwall at design, M2 0.80; (d) cavity endwall at design, M2 0.80; (e) flat endwall above design, M2 0.89; (f) cavity endwall above design, M2 0.89

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Figure 8

Pressure loss contours: (a) flat endwall below design, M2 0.69; (b) cavity endwall below, design M2 0.69; (c) flat endwall at design, M2 0.80; (d) cavity endwall at design, M2 0.80; (e) flat endwall above design, M2 0.89; (f) cavity endwall above design, M2 0.89

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Figure 7

Pitchwise mass averaged streamwise flow angle

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Figure 6

Mid-span blade loading of cavity cascade, typical of both cascades

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