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Research Papers: Gas Turbines: Turbomachinery

On Scaling Method to Investigate High-Speed Over-Tip-Leakage Flow at Low-Speed Condition

[+] Author and Article Information
Hongmei Jiang

University of Michigan-Shanghai Jiao Tong
University Joint Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China

Li He

Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK

Qiang Zhang

Department of Mechanical Engineering
and Aeronautics,
School of Engineering and Mathematical Sciences City,
University of London,
London EC1V 0HB, UK
e-mail: Qiang.Zhang@city.ac.uk

Lipo Wang

University of Michigan-Shanghai Jiao Tong University Joint Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 21, 2017; final manuscript received October 13, 2017; published online February 27, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(6), 062605 (Feb 27, 2018) (6 pages) Paper No: GTP-17-1524; doi: 10.1115/1.4038619 History: Received September 21, 2017; Revised October 13, 2017

Modern high-pressure turbine blades operate at high-speed conditions. The over-tip-leakage (OTL) flow can be high-subsonic or even transonic. From the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low-speed experiments. It has been assumed a redesigned low-speed blade profile with a matched blade loading should be sufficient to scale the high-speed OTL flow down to the low-speed condition. In this paper, the validity of this conventional scaling approach is computationally examined. The computational fluid dynamics (CFD) methodology was first validated by experimental data conducted in both high- and low-speed conditions. Detailed analyses on the OTL flows at high- and low-speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low-speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22%, and the total pressure loss at the low-speed condition is 6% higher than the high-speed case. An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be “scaled” down from the high-speed to low-speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally.

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Figures

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Fig. 5

Profile scaling process

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Fig. 4

Original high-speed blade profile and redesigned low-speed blade profile

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Fig. 3

Contours of heat transfer coefficient (a) high-speed case, P0,1/Ps,2 = 1.8, M2 = 0.86 and (b) low-speed case, P0,1/Ps,2 = 1.2, M2 = 0.45

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Fig. 2

Convergence of the nondimensional radially averaged OTL mass flux distribution on the suction side edge with different grid points

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Fig. 1

Setup of the computational domain and mesh

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Fig. 7

Mass flux ratio distribution at tip region above the suction side edge: (a) high speed and (b) low speed

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Fig. 6

Normalized Mach number distribution at middle span: (a) isentropic Mach number along blade surface and (b) Mach number contour

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Fig. 8

Comparison of normalized local tip leakage mass flow rate along suction-side curve length for the high-speed and low-speed cases

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Fig. 9

Radially averaged leakage mass flow vectors

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Fig. 10

Pressure coefficient Cp contours in the tip gap on the cut plane at s/S = 0.6 (as indicated)

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Fig. 11

Normalized local total pressure loss coefficient contour at 2 Cx cut plane: (a) high speed and (b) low speed

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Fig. 12

“Scaled down” low-speed tip gap height

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Fig. 13

Comparison of normalized local tip leakage mass flow rate along suction-side curve length for high-speed and low-speed reduced tip gap

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Fig. 14

Normalized local total pressure loss coefficient contour: (a) high-speed and (b) low-speed variable tip gap heights

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Fig. 15

Mach number distribution of cut plane s/S = 0.52: (a) high-speed and (b) low-speed reduced tip gap

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