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Research Papers

Secondary Flows in Low-Pressure Turbines Cascades: Numerical and Experimental Investigation of the Impact of the Inner Part of the Boundary Layer

[+] Author and Article Information
Matteo Giovannini

Departimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Matteo.Giovannini@tgroup.unifi.it

Filippo Rubechini

Departimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Filippo.Rubechini@tgroup.unifi.it

Michele Marconcini

Departimento di Ingegneria Industriale (DIEF),
Università degli Studi di Firenze,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: Michele.Marconcini@tgroup.unifi.it

Daniele Simoni

Dipartimento di Ingegneria meccanica,
energetica, gestionale e dei trasporti (DIME),
Università di Genova,
Via Montallegro, 1,
Genova 16145, Italy
e-mail: daniele.simoni@unige.it

Vianney Yepmo

Dipartimento di Ingegneria meccanica,
energetica, gestionale e dei trasporti (DIME),
Università di Genova,
Via Montallegro, 1,
Genova 16145, Italy
e-mail: vianney.yepmo.henang@edu.unige.it

Francesco Bertini

Avio Aero,
Via I Maggio 99,
Rivalta di Torino (TO) 10040, Italy
e-mail: Francesco.Bertini@avioaero.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 8, 2018; final manuscript received August 29, 2018; published online October 8, 2018. Editor: Kenneth Hall.

J. Turbomach 140(11), 111002 (Oct 08, 2018) (12 pages) Paper No: TURBO-18-1192; doi: 10.1115/1.4041378 History: Received August 08, 2018; Revised August 29, 2018

Due to the low level of profile losses reached in low-pressure turbines (LPT) for turbofan applications, a renewed interest is devoted to other sources of loss, e.g., secondary losses. At the same time, the adoption of high-lift profiles has reinforced the importance of these losses. A great attention, therefore, is dedicated to reliable prediction methods and to the understanding of the mechanisms that drive the secondary flows. In this context, a numerical and experimental campaign on a state-of-the-art LPT cascade was carried out focusing on the impact of different inlet boundary layer (BL) profiles. First of all, detailed Reynolds Averaged Navier-Stokes (RANS) analyzes were carried out in order to establish dependable guidelines for the computational setup. Such analyzes also underlined the importance of the shape of the inlet BL very close to the endwall, suggesting tight requirements for the characterization of the experimental environment. The impact of the inlet BL on the secondary flow was experimentally investigated by varying the inlet profile very close to the endwall as well as on the external part of the BL. The effects on the cascade performance were evaluated by measuring the span-wise distributions of flow angle and total pressure losses. For all the inlet conditions, comparisons between Computational Fluid Dynamics (CFD) and experimental results are discussed. Besides providing guidelines for a proper numerical and experimental setup, the present paper underlines the importance of a detailed characterization of the inlet BL for an accurate assessment of the secondary flows.

Copyright © 2018 by ASME
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Figures

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Fig. 3

Sketch of the test rig

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Fig. 2

Blade loading near endwall and at midspan (fully turbulent calculation with inviscid endwall)

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Fig. 1

Blade loading at cascade mid span

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Fig. 4

Cell clustering in span-wise direction

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Fig. 8

Analytical total pressure distribution. Different locations of the first point above the wall.

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Fig. 9

Impact of the inlet BL sampling on secondary flows

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Fig. 10

Experimental inlet total pressure distribution. Different near-wall shapes below the first measured point.

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Fig. 11

Impact of the inlet near-wall BL on secondary flows

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Fig. 12

Experimental distributions of inlet total pressure. Original and wall-refined measurements.

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Fig. 13

Comparison between measured and computed span-wise distributions at cascade exit. Impact of the inlet near-wall characterization.

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Fig. 5

Mesh details near hub endwall

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Fig. 6

Grid dependence analysis: distributions of blade-to-blade angle and total pressure loss along the span

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Fig. 7

Grid dependence analysis: contour plots of losses at cascade exit

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Fig. 14

Measurements versus CDF. Fully turbulent and transitional results.

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Fig. 15

Sketch of the test-rig upstream of the blade leading edge. Closed and opened slot for BL suction.

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Fig. 16

Span-wise profile of the three inlet BLs

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Fig. 17

Contour plots of total pressure loss coefficient at cascade exit. Comparison between measurements and calculations.

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Fig. 18

Measured and computed span-wise distributions of blade-to-blade angle and total pressure loss at cascade exit

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Fig. 19

Contour plots of total pressure loss and SWV over a plane normal to the exit flow direction

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Fig. 20

Secondary losses at varying inlet BL

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Fig. 21

Span-wise distribution of the normal-like component of vorticity at cascade inlet

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