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Research Papers

Aerodynamic Interaction Between an Incoming Vortex and Tip Leakage Flow in a Turbine Cascade

[+] Author and Article Information
Kai Zhou

BIC-ESAT,
Peking University,
Beijing 100871, China
e-mail: kinozhou@pku.edu.cn

Chao Zhou

Turbomachinery Laboratory,
College of Engineering; BICESAT,
Peking University,
Beijing 100871, China
e-mail: czhou@pku.edu.cn

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 6, 2018; final manuscript received September 13, 2018; published online October 8, 2018. Editor: Kenneth Hall.

J. Turbomach 140(11), 111004 (Oct 08, 2018) (12 pages) Paper No: TURBO-18-1235; doi: 10.1115/1.4041514 History: Received September 06, 2018; Revised September 13, 2018

In turbines, secondary vortices and tip leakage vortices form in the blade passage and interact with each other. In order to understand the flow physics of this vortices interaction, the effects of incoming vortex on the downstream tip leakage flow are investigated by experimental, numerical, and analytical methods. In the experiment, a swirl generator was used upstream of a linear turbine cascade to generate the incoming vortex, which could interact with the downstream tip leakage vortex (TLV). The swirl generator was located at ten different pitchwise locations to simulate the quasi-steady effects. In the numerical study, a Rankine-like vortex was defined at the inlet of the computational domain to simulate the incoming swirling vortex (SV). The effects of the directions of the incoming vortices were investigated. In the case of a positive incoming SV, which has a large vorticity vector in the same direction as that of the TLV, the vortex mixes with the TLV to form one major vortex near the casing as it transports downstream. This vortices interaction reduces the loss by increasing the streamwise momentum within the TLV core. However, the negative incoming SV has little effects on the TLV and the loss. As the negative incoming SV transports downstream, it travels away from the TLV and two vortices can be identified near the casing. A triple-vortices-interaction kinetic model is used to explain the flow physics of vortex interaction, and a one-dimensional mixing analytical model are proposed to explain the loss mechanism.

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Figures

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Fig. 1

Experimental facility: (a) layout of the cascade, (b) illustration of the relative position of swirl generator and blade, and (c) measurement location for endwall inlet boundary layer

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Fig. 2

Geometry of swirl generators: (a) PSG, (b) NuSG, and (c) NSG

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Fig. 3

Distribution of stagnation pressure coefficient and velocity vector, 0.18Cx downstream of the swirl generator: (a) PSG, (b) NuSG, and (c) NSG

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Fig. 4

Streamwise vorticity for PSG, 0.18Cx and 0.27Cx downstream of the swirl generator: (a) 0.18Cx and (b) 0.27Cx

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Fig. 5

Computational domain and mesh: (a) computational domains and (b) mesh near tip gap A and trailing edge B

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Fig. 6

Tangential and axial velocity of the vortex model

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Fig. 7

Circulation at different locations downstream of the swirl generator and CFD dissipation

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Fig. 8

Nondimensional streamwise vorticity, circulation and streamwise velocity on the monitor plane for CFD and experiment: (a) CFD, (b) EXP, (c) circulation, and (d) streamwise velocity

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Fig. 9

Cp around the blade surface at middle Span, the case with uniform inlet condition

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Fig. 10

CP0 at cut plane 2, the case with uniform inlet condition: (a) EXP and (b) CFD

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Fig. 11

Mass-weighted averaged CP0 along the spanwise direction, the case with uniform inlet condition

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Fig. 12

Definition for phase of the swirl generators

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Fig. 13

CP0 on the plane 2, the case with PSG, Exp: (a) φ = 1/10, (b) φ = 3/10, (c) φ = 5/10, (d) φ = 7/10, and (e) φ = 9/10

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Fig. 14

CP0 on the plane 2: case with (a) PSG, (b) NuSG, and (c) NSG at φ = 9/10, Exp

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Fig. 15

Mass-weighted-averaged CP0 along the spanwise direction at phases of max and min TLV loss

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Fig. 16

CP0 on the plane 2, incoming positive vortex, CFD: (a) φ = 1/10, (b) φ = 3/10, (c) φ = 5/10, (d) φ = 7/10, and (e) φ = 9/10

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Fig. 17

CP0 along streamwise direction, incoming PSV: (a) φ = 5/10 and (b) φ = 9/10

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Fig. 18

The vortex transportation of incoming SV at phase φ = 9/10, Isosurface of scalar Ω = 0.2: (a) positive swirling flow and (b) negative swirling flow

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Fig. 19

Relative CP0 along spanwise direction in several axial locations

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Fig. 20

Instantaneous time for the locations of four ribbons, phase φ = 9/10: (a) PSG, (b) NSG, and (c) view angle

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Fig. 21

Nondimensional streamwise vorticity distribution, incoming positive swirling flow: (a) φ = 5/10 and (b) φ = 9/10

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Fig. 22

Mixed-out loss for different inlet conditions, CFD

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Fig. 23

Schematic of a triple-vortices-interaction kinetic model

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Fig. 24

Schematic of 1D mixing model of two square wake deficits

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Fig. 25

The difference in loss ΔEk(%) for two different mixing ways, VTLV = 0.36 and VSV = 0.85

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