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Research Papers

Aerodynamic Optimization of a Winglet-Shroud Tip Geometry for a Linear Turbine Cascade

[+] Author and Article Information
Min Zhang

Key Laboratory of Ocean Energy Utilization and
Energy Conservation of Ministry of Education,
School of Energy and Power Engineering,
Dalian University of Technology,
No. 2 Linggong Road, Ganjingzi District,
Dalian 116024, China
e-mail: modest_zm@126.com

Yan Liu

Key Laboratory of Ocean Energy Utilization and
Energy Conservation of Ministry of Education,
School of Energy and Power Engineering,
Dalian University of Technology,
No. 2 Linggong Road, Ganjingzi District,
Dalian 116024, China
e-mail: yanliu@dlut.edu.cn

Tianlong Zhang

School of Energy and Power Engineering,
Dalian University of Technology,
No. 2 Linggong Road, Ganjingzi District,
Dalian 116024, China
e-mail: zhtl369@163.com

Mengchao Zhang

School of Energy and Power Engineering,
Dalian University of Technology,
No. 2 Linggong Road, Ganjingzi District,
Dalian 116024, China
e-mail: mczdlut@163.com

Ying He

School of Energy and Power Engineering,
Dalian University of Technology,
No. 2 Linggong Road, Ganjingzi District,
Dalian 116024, China
e-mail: heying@dlut.edu.cn

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 23, 2016; final manuscript received March 29, 2017; published online June 6, 2017. Editor: Kenneth Hall.

J. Turbomach 139(10), 101011 (Jun 06, 2017) (9 pages) Paper No: TURBO-16-1125; doi: 10.1115/1.4036647 History: Received June 23, 2016; Revised March 29, 2017

This paper presents a continued study on a previously investigated novel winglet-shroud (WS) (or partial shroud) geometry for a linear turbine cascade. Various widths of double-side winglets (DSW) and different locations of a partial shroud are considered. In addition, both a plain tip and a full shroud tip are applied as the datum cases which were examined experimentally and numerically. Total pressure loss and viscous loss coefficients are comparatively employed to execute a quantitative analysis of aerodynamic performance. The effectiveness of various widths (w) of DSW set at 3%, 5%, 7%, and 9% of the blade pitch (p) is numerically investigated. Skin-friction lines on the tip surface indicate that different DSW cases do not alter flow field features including the separation bubble and reattachment flow within the tip gap region, even for the case with the broadest width (w/p = 9%). However, the pressure side extension of the DSW exhibits the formation of separation bubble, while the suction side platform of the DSW turns the tip leakage vortex (TLV) away from the suction surface (SS). Meanwhile, the horse-shoe vortex (HV) near the casing is not generated even for the case with the smallest width (w/p = 3%). As a result, both the tip leakage and the upper passage vortices are weakened and further dissipated with wider w/p in the DSW cases. Larger width of the DSW geometry is indeed able to improve the aerodynamic performance, but only to a slight degree. With the w/p increasing from 3% to 9%, the mass-averaged total pressure loss coefficient over an exit plane is reduced by only 2.61%. Therefore, considering both the enlarged (or reduced) tip area and the enhanced (or deteriorated) performance compared to the datum cases, a favorable width of w/p = 5% is chosen to design the WS structure. Three locations for the partial shroud (linkage segment) are devised, locating them near the leading edge, in the middle and close to the trailing edge, respectively. Results demonstrate that all three cases of the WS design have advantages over the DSW arrangement in lessening the aerodynamic loss, with the middle linkage segment location producing the optimal effect. This conclusion verifies the feasibility of the previously studied WS configuration.

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Figures

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Fig. 1

Design process of the winglet-shroud geometry

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Fig. 3

Experimental cascade

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Fig. 4

Computational domain

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Fig. 5

Distribution of Cpt and secondary flow streamlines: (a) in case 1, CFD, (b) in case 2, CFD, and (c) on the upper span area of 1.36Cax plane, EXP

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Fig. 6

Axial distributions of Cpt and wvis for cases 1 and 2

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Fig. 7

Loss breakdown for cases 1–6

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Fig. 8

Contours of Sv on the upper half span area of 1.36Cax plane: (a) case 3, (b) case 4, (c) case 5, and (d) case 6

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Fig. 9

Contours of Cps on the tip surfaces for cases 1–6 and axial distributions of Cps on the blade surface at 97.5%h for cases 1 and 3–6

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Fig. 10

Flow features on the casing: (a) case 1 and (b) case 6

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Fig. 11

Flow features on various axial planes: (a) case 7, (b) case 8, and (c) case 9

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Fig. 12

Axial distributions of Cps and loss breakdown for cases 7–9

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Fig. 13

Predicted tip leakage mass flow rates for cases 1, 4, and 7–9

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