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Research Papers

Riblet Application in Compressors: Toward Efficient Blade Design

[+] Author and Article Information
Alexander Hergt

German Aerospace Center (DLR),
Institute of Propulsion Technology,
Cologne 51147, Germany
e-mail: alexander.hergt@dlr.de

W. Hage, S. Grund

German Aerospace Center (DLR),
Institute of Propulsion Technology,
Cologne 51147, Germany

W. Steinert

German Aerospace Center (DLR),
Institute of Propulsion Technology,
Cologne 51147, Germany

M. Terhorst, F. Schongen

Laboratory for Machine Tools and
Production Engineering,
RWTH Aachen University,
Aachen 52074, Germany

Y. Wilke

Fraunhofer Institute for Manufacturing,
Technology and Advanced Materials IFAM,
Bremen 28359, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received May 25, 2015; final manuscript received June 12, 2015; published online September 16, 2015. Assoc. Editor: Michael Hathaway.

J. Turbomach 137(11), 111006 (Sep 16, 2015) (12 pages) Paper No: TURBO-15-1103; doi: 10.1115/1.4031090 History: Received May 25, 2015

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step toward more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number (LRN) conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5 × 105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 deg. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” was used for the optimization process. The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5 × 105–9.0 × 105. Furthermore, the measurements were carried out at a low turbulence level of 0.8% and at a high turbulence level of 4%, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study, riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating techniques, were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets (CRs) have a width of 50 μm. The wake measurements were performed using a three-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Optimization process chain

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Fig. 2

Blade parametrization

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Fig. 3

Sketch of riblets and their characterizing parameters [14]

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Fig. 4

Result of the optimization (data base)

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Fig. 5

Numerical loss-inflow angle characteristics of the final member (turbulence intensity of 0.8%)

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Fig. 6

Distribution of the nondimensional riblet groove spacing on the blade suction and pressure side (left), general structure of a drag reduction curve of riblets [14] (right)

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Fig. 7

Principle of the riblet rolling process

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Fig. 8

Occurrence of shear forces due to the lateral offset

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Fig. 9

Riblets produced by riblet rolling of seven Ti6Al4V-specimes

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Fig. 10

Tool feeding for the structuring of compressor blades

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Fig. 11

Riblets produced by riblet rolling of compressor blades made of 42CrMo4

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Fig. 12

Blade distorsion due to nonuniform induced residual stresses [23]

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Fig. 13

Application of the riblet structured surface

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Fig. 14

Negative silicone mold (top), compressor blade coated with riblets (bottom)

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Fig. 15

Schematic of the riblet coating

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Fig. 16

SEM-picture of the riblet structure

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Fig. 17

LRN-OGV cascade for wind tunnel test (five of seven blades are shown)

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Fig. 18

Cross section of the DLR transonic cascade wind tunnel

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Fig. 19

Cascade parameters, definition of measurement planes, and boundary layer suction design

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Fig. 20

Loss-inflow angle characteristics of the datum, RR and CR cascade at different Reynolds numbers (Tu = 0.8)

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Fig. 21

Comparison of the total pressure ratio pt,2/pt,1 wake between the datum and RR (left), CR (right) cascades at OP 1, Re = 1.5 × 105 (Tu = 0.8)

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Fig. 22

Experimental and numerical profile Mach number distribution of the LRN-OGV datum cascade at OP 1 at Re = 1.5 × 105 with Tu = 0.8 (left) and Tu = 4.0 (right)

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Fig. 23

Loss-inflow angle characteristics of the datum, RR and CR cascades at different Reynolds numbers (Tu = 4.0)

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Fig. 24

Comparison of the total pressure ratio pt,2/pt,1 wake between the datum and RR (left), CR (right) cascades at OP 1, Re = 1.5 × 105 (Tu = 4.0)

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Fig. 25

Comparison of the total pressure ratio pt,2/pt,1 wake between the datum and RR (left), CR (right) cascades at OP 1, Re = 2.5 × 105 (Tu = 4.0)

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