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Research Papers: Gas Turbines: Turbomachinery

Heat Transfer of Winglet Tips in a Transonic Turbine Cascade

[+] Author and Article Information
Fangpan Zhong

State Key Laboratory for Turbulence and
Complex Systems,
College of Engineering,
Peking University,
Beijing 100871, China
e-mail: zhongfp@pku.edu.cn

Chao Zhou

State Key Laboratory for Turbulence and
Complex Systems,
College of Engineering,
Peking University,
Beijing 100871, China;
Collaborative Innovation Center of
Advanced Aero-Engine,
Beijing 100191, China
e-mail: czhou@pku.edu.cn

H. Ma

University of Michigan-Shanghai Jiao Tong Joint
Institute,
Shanghai Jiao Tong University,
UM-SJTU JI,
800 Dongchuan Road,
Minhang District,
Shanghai 200240, China
e-mail: haitengma@gmail.com

Q. Zhang

University of Michigan-Shanghai
Jiao Tong Joint Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: Qiang.Zhang.1@city.ac.uk

1Corresponding author.

2Present address: Department of Mechanical Engineering and Aeronautics, City University London, Northampton Square EC1V 0HB, London.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 19, 2016; final manuscript received June 28, 2016; published online September 8, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(1), 012605 (Sep 08, 2016) (11 pages) Paper No: GTP-16-1231; doi: 10.1115/1.4034208 History: Received June 19, 2016; Revised June 28, 2016

Understanding the heat transfer of winglet tips is crucial for their applications in high-pressure turbines. The current paper investigates the heat transfer performance of three different winglet-cavity tips in a transonic turbine cascade at a tip gap of 2.1% chord. A cavity tip is studied as the baseline case. The cascade operates at engine representative conditions of an exit Mach number of 1.2 and an exit Reynolds number of 1.7 × 106. Transient infrared thermography technique was used to obtain the tip distributions of heat transfer coefficient for different tips in the experiment. The CFD results were validated with the measured tip heat transfer coefficients, and then used to explain the flow physics related to heat transfer. It is found that on the pressure side winglet, the flow reattaches on the top winglet surface and results in high heat transfer coefficient. On the suction side winglet, the heat transfer coefficient is low near the blade leading edge but is higher from the midchord to the trailing edge. The suction side winglet pushes the tip leakage vortex further away from the blade suction surface and reduces the heat transfer coefficient from 85% to 96% span on the blade suction surface. However, the heat transfer coefficient is higher for the winglet tips from 96% span to the tip. This is because the tip leakage vortex attaches on the side surface of the suction side winglet and results in quite high heat transfer coefficient on the front protrusive part of the winglet. The effects of relative endwall motion between the blade tip and the casing were investigated by CFD method. The endwall motion has a significant effect on the flow physics within the tip gap and near-tip region in the blade passage, thus affects the heat transfer coefficient distributions. With relative endwall motion, a scraping vortex forms inside the tip gap and near the casing, and the cavity vortex gets closer to the pressure side squealer/winglet. The tip leakage vortex in the blade passage becomes closer to the blade suction surface, resulting in an increase of the heat transfer coefficient.

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References

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Figures

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Fig. 1

Schematic and picture of the cascade table: (a) schematic diagram (b) picture

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Fig. 2

IR camera and ZnSe window

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Fig. 3

Measurement system

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Fig. 4

Typical inlet flow total pressure and total temperature history

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Fig. 5

Geometries of cavity and winglet tips: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 6

Computational domain and mesh of winglet tip “PSW”

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Fig. 7

Isentropic Mach number on the midspan of the blade with cavity tip, CFD

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Fig. 8

Tip flow streamlines of cavity tip, CFD

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Fig. 9

Mach number distributions on the middle plane of the tip gap, CFD: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 10

Dimensionless mass flow rate distributions at tip gap exit, CFD

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Fig. 11

Mach number distributions of cavity tip and winglet tip “SSW” on the cut plane ‘1’ indicated in Fig. 9(a), CFD

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Fig. 12

Cp0 distributions on the cut plane ‘2’ indicated in Fig. 9(d), CFD: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 13

HTC distributions on near-tip region of blade suction surface (W/m2 K), CFD: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 14

Spanwise area-averaged HTC distributions around the blade suction surface, CFD

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Fig. 15

Tip HTC distribution of cavity tip (W/m2 K): (a) EXP and (b) CFD

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Fig. 16

Computational and experimental HTC distribution along line ‘1’ shown in Fig. 15(b) of cavity tip

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Fig. 17

Tip HTC distributions of three winglet tips (W/m2 K): (a) EXP and (b) CFD

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Fig. 18

Mach number distributions on the middle plane of the tip gap of all tips with endwall motion: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 19

Dimensionless mass flow rate distributions at tip gap exit with endwall motion

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Fig. 20

Tip flow streamlines released from 10% gap height above the tip of “PSW”: (a) stationary and (b) moving

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Fig. 21

Tip flow streamlines released from 90% gap height above the tip of “PSW”: (a) stationary and (b) moving

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Fig. 22

Tip HTC distributions of the cavity tip and winglet tips with endwall motion: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 23

HTC distributions near-tip region on the suction side surface with endwall motion: (a) cavity, (b) SSW, (c) SFW, and (d) PSW

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Fig. 24

Spanwise area-averaged HTC distributions around the blade suction surface with endwall motion

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