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Research Papers

Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades

[+] Author and Article Information
Helmut Sauer, Konrad Vogeler

Institute of Fluid Mechanics, Technische Universität Dresden, D-01062 Dresden, Germany

Robin Schmidt

Institute of Fluid Mechanics, Technische Universität Dresden, D-01062 Dresden, Germanyrobin.schmidt@tu-dresden.de

J. Turbomach 134(1), 011015 (May 27, 2011) (9 pages) doi:10.1115/1.4003244 History: Received September 14, 2010; Revised October 25, 2010; Published May 27, 2011; Online May 27, 2011

In this paper, results concerning the influence of chord length and inlet boundary layer thickness on the endwall loss of a linear turbine cascade are discussed. The investigations were performed in a low speed cascade tunnel using the turbine profile T40. The turning of 90 deg and 70 deg, the velocity ratio in the cascade from 1.0 to 3.5 as well as the chord length of 100 mm, 200 mm, and 300 mm were specified. In a measurement distance of one chord behind the cascade in main flow direction, an approximate proportionality of endwall loss and chord was observed in a wide range of velocity ratios. At small measurement distances (e.g., s2/l=0.4), this proportionality does not exist. If a part of the flow path within the cascade is approximately incorporated, a proportionality to the chord at small measurement distances can be obtained, too. Then, the magnitude of the endwall loss mainly depends on the distance in main flow direction. At velocity ratios near 1.0, the influence of the chord decreases rapidly, while at a velocity ratio of 1.0, the endwall loss is independent of the chord. By varying the inlet boundary layer thickness, no correlation of displacement thickness and endwall loss was achieved. A calculation method according to the modified integral equation by van Driest delivers the wall shear stress. Its influence on the endwall loss was analyzed.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Secondary vortices in a turbine cascade

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Figure 2

Distribution of boundary layer thickness on the suction side (5)

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Figure 3

Distribution of endwall losses in a vane cascade (8)

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Figure 4

Cascade geometry

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Figure 5

Profile pressure distributions for Θ=90 deg

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Figure 6

Local loss distribution (β1=63.5 deg, Θ=90 deg, t/l=0.7, v=2, s2/l=1, and δ1,1≈3 mm)

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Figure 7

Pitchwise averaged losses

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Figure 8

Endwall loss versus flow path behind the cascade at v=2

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Figure 9

Reduced endwall loss at different aspect ratios (Θ, v, and s2/l)

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Figure 10

Endwall loss in different measuring planes including the development in the cascade (l, Θ, and v)

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Figure 11

Endwall loss at different turnings, velocity ratios, and chord lengths at s2/l=1

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Figure 12

Exponent n to characterize the proportionality at s2/l=1

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Figure 13

Endwall loss over (a) displacement thickness and (b) local coefficient of friction (l, Θ, and v)

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