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Research Papers

Experimental and Numerical Investigation of Optimized Blade Tip Shapes—Part I: Turbine Rainbow Rotor Testing and Numerical Methods

[+] Author and Article Information
Bogdan C. Cernat

Turbomachinery and Propulsion Department,
von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse 1640, Belgium
e-mail: cernat@vki.ac.be

Marek Pátý

Turbomachinery and Propulsion Department,
von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse 1640, Belgium
e-mail: marek.paty@seznam.cz

Cis De Maesschalck

von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse 1640, Belgium
e-mail: cis.demaesschalck@gmail.com

Sergio Lavagnoli

Assistant Professor
Turbomachinery and Propulsion Department,
von Karman Institute for Fluid Dynamics,
Rhode Saint Genèse 1640, Belgium
e-mail: lavagnoli@vki.ac.be

1Corresponding author.

2Present address: CTU, Prague 166 36, Czech Republic.

3Present address: Rolls-Royce plc, Derby DE 21 7BB, UK.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 22, 2018; final manuscript received September 8, 2018; published online December 20, 2018. Editor: Kenneth Hall.

J. Turbomach 141(1), 011006 (Dec 20, 2018) (13 pages) Paper No: TURBO-18-1219; doi: 10.1115/1.4041465 History: Received August 22, 2018; Revised September 08, 2018

Blade tip design and tip leakage flows are crucial aspects for the development of modern aero-engines. The inevitable clearance between stationary and rotating parts in turbine stages generates high-enthalpy unsteady leakage flows that strongly reduce the engine efficiency and can cause thermally induced blade failures. An improved understanding of the tip flow physics is essential to refine the current design strategies and achieve increased turbine aerothermal performance. However, while past studies have mainly focused on conventional tip shapes (flat tip or squealer geometries), the open literature suffers from a shortage of experimental and numerical data on advanced blade tip configurations of unshrouded rotors. This work presents a complete numerical and experimental investigation on the unsteady flow field of a high-pressure turbine, adopting three different blade tip profiles. The aerothermal characteristics of two novel high-performance tip geometries, one with a fully contoured shape and the other presenting a multicavity squealer-like tip with partially open external rims, are compared against the baseline performance of a regular squealer geometry. The turbine stage is tested at engine-representative conditions in the high-speed turbine facility of the von Karman Institute. A rainbow rotor is mounted for simultaneous aerothermal testing of multiple blade tip geometries. On the rotor disk, the blades are arranged in sectors operating at two different clearance levels. A numerical campaign of full-stage simulations was also conducted on all the investigated tip designs to model the secondary flows development and identify the tip loss and heat transfer mechanisms. In the first part of this work, we describe the experimental setup, instrumentation, and data processing techniques used to measure the unsteady aerothermal field of multiple blade tip geometries using the rainbow rotor approach. We report the time-average and time-resolved static pressure and heat transfer measured on the shroud of the turbine rotor. The experimental data are compared against numerical predictions. These numerical results are then used in the second part of the paper to analyze the tip flow physics, model the tip loss mechanisms, and quantify the aero-thermal performance of each tip geometry.

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Figures

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Fig. 1

Investigated tip geometries: (a) single squealer, (b) optimized squealer, and (c) contoured profile

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Fig. 2

Evolution of the tip profiles along the blade

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Fig. 3

Turbine rig and test section

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Fig. 4

Rainbow rotor configuration

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Fig. 5

Experimental inlet profiles

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Fig. 6

Casing instrumentation: (a) static pressure insert, (b) heat transfer insert, and (c) detail of a thin-film gauge

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Fig. 7

Phase-locked averaging technique and blade sector data reduction

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Fig. 8

Statistical convergence of ensemble-average parameters for casing static pressure measurements

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Fig. 9

CFD setup: (a) numerical domain, (b) tip y+ distribution, and (c) tip unstructured mesh

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Fig. 10

Measured and predicted time-average casing static pressure: (a) rotor pitch, (b) rotor passage, and (c) overtip

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Fig. 11

Measured and predicted time-average casing heat transfer: (a) rotor pitch, (b) rotor passage, and (c) overtip

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Fig. 12

Measured and predicted time-resolved casing static pressure and heat transfer fluctuations of the three tip blade geometries as a function of the rotor phase at selected axial positions

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Fig. 13

Experimental time-resolved casing static pressure for the three blade tips (left IN01D, center AC06D, right AC07T): phase-locked static pressure (first row from top), random unsteadiness (second row), maximum amplitude of rows interaction (third row)

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Fig. 14

Experimental time-resolved casing heat transfer for the three blade tips (left IN01D, center AC06D, right AC07T): phase-locked heat transfer (first row from top), random unsteadiness (second row), maximum amplitude of row interaction (third row)

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