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Research Papers: Flows in Complex Systems

Numerical and Experimental Investigations of the Three-Dimensional-Flow Structure of Tandem Cascades in the Sidewall Region

[+] Author and Article Information
Martin Böhle

Professor
Chair of Fluid Mechanics and Fluid Machinery,
Department of Mechanical and
Process Engineering,
Technical University Kaiserslautern,
Gottlieb Daimler Strasse,
Kaiserslautern 67663, Germany
e-mail: martin.boehle@mv.uni-kl.de

Thomas Frey

Chair of Fluid Mechanics and Fluid Machinery,
Department of Mechanical and
Process Engineering,
Technical University Kaiserslautern,
Gottlieb Daimler Strasse,
Kaiserslautern 67663, Germany
e-mail: thomas.frey@mv.uni-kl.de

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 4, 2013; final manuscript received February 13, 2014; published online May 6, 2014. Assoc. Editor: Zvi Rusak.

J. Fluids Eng 136(7), 071102 (May 06, 2014) (13 pages) Paper No: FE-13-1220; doi: 10.1115/1.4026880 History: Received April 04, 2013; Revised February 13, 2014

Tandem blades can be superior to single blades, particularly when large turning angles are required. This is well documented in the open literature and many investigations have been performed on the 2D-flow of tandem cascades to date. However, much less information on the flow near the sidewalls is available. Thus, the question arises as to how the geometry of a tandem cascade should be chosen near the sidewall in order to minimize the flow losses for large turning angles. The present work examines the 3D-flow field in the region of the sidewall of two high turning tandem cascades. A large spacing ratio was chosen for the forward blade of the first tandem cascade ((t/l)1=1.92). The second tandem cascade possessed a smaller spacing ratio for the forward blades ((t/l)1=1.0). Both cascades had the same total spacing ratio of t/l=0.6. Flow phenomena, such as the corner stall of the 3D boundary layer near the sidewall, are examined using both numerical and experimental methods. The empirical correlations of Lieblein and Lei are applied. The flow topology of both tandem cascades is explained and the locations of loss onset are identified. In addition, oil pictures from experiments and streamline pictures of the numerical simulations are shown and discussed for the flow close to the sidewalls. Finally, design rules such as the aerodynamic load splitting and the spacing ratio of the forward- and aft-blades, etc. are taken into account. The examinations are performed for tandem cascades designed for flow turning of approximately 50deg at a Reynolds number of 8×105. The tandem cascades consist of NACA65 blades with circular camber lines and an aspect ratio of b/l=1.0.

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References

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Figures

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Fig. 1

Nomenclature of the tandem cascade

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Fig. 2

Cascade A and cascade B

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Fig. 3

Diffusion numbers, load split, and (t/l)2 in dependence of the spacing ratio

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Fig. 4

Calculation domain

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Fig. 5

Velocity profile on inlet

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Fig. 6

2D-numerical result: ζ¯ and Δβ in dependence of β11

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Fig. 7

3D-Numerical result: ζ¯ and Δβ in dependence of β11; losses were mass averaged over the whole exit plane (see the light-gray diamond shaped plane of Fig. 4)

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Fig. 8

Numerical result: streamlines close to the sidewall of cascade A, β11 = 50 deg

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Fig. 9

Numerical result: streamlines close to the sidewall of cascade B, β11= 50 deg

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Fig. 10

Numerical result: streamlines close to the sidewall of cascade A, β11 = 54 deg

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Fig. 11

Numerical result: streamlines close to the sidewall of cascade B, β11 = 54 deg

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Fig. 12

Numerical result: ζ-distribution of cascade A, β11 = 50 deg

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Fig. 13

Numerical result: ζ-distribution of cascade B, β11 = 50 deg

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Fig. 14

Numerical result: ζ-distribution of cascade A, β11 = 54 deg

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Fig. 15

Numerical result: ζ-distribution of cascade B, β11 = 54 deg

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Fig. 16

Numerical result (qualitative): ζ-distribution in tandem cascade B, β11 = 54 deg

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Fig. 17

Cascade wind tunnel

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Fig. 18

Five hole probe, angles, and velocity components

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Fig. 19

Measured flow losses at midspan in comparison with the numerical results for cascades A and B

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Fig. 20

Cascade A: measured and calculated flow losses in the wake at midspan for β11 = 50 deg and β11 = 54 deg

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Fig. 21

Cascade B: measured and calculated flow losses in the wake at midspan for β11 = 50 deg and  oβ11 = 54 deg

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Fig. 22

Cascade A: local measured flow losses for β11 = 50 deg and β11 = 54 deg

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Fig. 23

Cascade B: local measured flow losses for β11 = 50 deg and β11 = 54 deg

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Fig. 24

Cascade A: oil picture for β11 = 50 deg

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Fig. 25

Cascade A: oil picture for β11 = 54 deg

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Fig. 26

Cascade B: oil picture for β11 = 50 deg

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Fig. 27

Cascade B: oil picture for β11 = 54 deg

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