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Research Papers

Optimal Application of Riblets on Compressor Blades and Their Contamination Behavior

[+] Author and Article Information
Christoph Lietmeyer

Research Assistant
Institute of Turbomachinery and Fluid Dynamics,
Leibniz Universitaet Hannover,
30167 Hannover, Germany
e-mail: Lietmeyer@tfd.uni-hannover.de

Karsten Oehlert

Power Plant Engineer,
E.ON Nuclear Energy GmbH,
30457 Hannover, Germany
e-mail: Karsten.Oehlert@eon-energie.com

Joerg R. Seume

Senior Member ASME
Professor
Institute of Turbomachinery and Fluid Dynamics,
Leibniz Universitaet Hannover,
30167 Hannover, Germany
e-mail: Seume@tfd.uni-hannover.de

Contributed by International Gas Turbine Institute (IGTI) of ASME for publication in JOURNAL OF TURBOMACHINERY. Manuscript received July 21, 2011; final manuscript received August 30, 2011; published online October 31, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011036 (Oct 31, 2012) (10 pages) Paper No: TURBO-11-1155; doi: 10.1115/1.4006518 History: Received July 21, 2011; Revised August 30, 2011

During the last decades, riblets have shown a potential for viscous drag reduction in turbulent boundary layers. Several investigations and measurements of skin-friction in the boundary layer over flat plates and on turbomachinery-type blades with ideal riblet geometry have been reported in the literature. The question of where riblets must be applied on the surface of a compressor blade is still not sufficiently answered. In a first step, the profile loss reduction by ideal triangular riblets with a trapezoidal groove and a constant geometry along the surface on the suction and pressure sides of a compressor blade is investigated. The results show a higher potential on the profile loss reduction by riblets on the suction side. In a second step, the effect of laser-structured ribs on the laminar separation bubble and the influence of these structures on the laminar boundary layer near the leading edge are investigated. After clarifying the best choices where riblets should be applied on the blade surface, a strategy for locally adapted riblets is presented. The suction side of a compressor blade is laser-structured with segmented riblets with a constant geometry in each segment. The measured profile loss reduction shows the increasing effect on the profile loss reduction of this locally adapted structure compared to a constant riblet-geometry along the surface. Furthermore, the particle deposition on a riblet-structured compressor blade is investigated and compared to the particle deposition on a smooth surface. Results show a primary particle deposition on the riblet tips followed by an agglomeration. The particle deposition on the smooth surface is stochastic.

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References

Figures

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Fig. 1

Low speed streaks in viscous sublayer (Van Dyke [12])

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Fig. 2

Vortices in the viscous sublayer (Van Dyke [12])

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Fig. 3

Viscous longitudinal and cross flow on a ribbed surface with Δh=hpl−hpc (Bechert et al. [13])

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Fig. 4

The effect of different riblet geometries on wall shear stress (Bechert et al. [5])

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Fig. 5

Definition of angles (Wilson and Korakianitis [17])

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Fig. 6

Mises calculation of ideal riblet width for s+ = 17 and comparison to the chosen constant riblet width s = 40 μm

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Fig. 7

Calculated reduction of wall shear stress according to the chosen riblet width s

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Fig. 8

Designed riblet geometry

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Fig. 9

Linear cascade wind tunnel (Harbecke [15])

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Fig. 10

Blade cascade with boundary layer suction and wake traverse system with double wedge-type probes

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Fig. 11

Pressure coefficient Cp for alpha_in = 60 deg

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Fig. 12

Experimental setup for dust contamination measurements

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Fig. 13

Blade sections for dust contamination measurements

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Fig. 14

Ideal riblet structure (source: IMR)

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Fig. 15

Comparison of blade thickness: riblet versus smooth

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Fig. 16

Laminar separation bubble near the LE taken in the linear cascade wind tunnel (oil picture)

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Fig. 17

Surface structure of the laser-structured blade L3 (source: IMR)

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Fig. 18

s+ distribution along the suction side for a constant riblet width of s = 40 μm

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Fig. 19

s+ distribution along the suction side for segmented riblets

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Fig. 20

Surface structure of the laser-structured blade (source: IMR)

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Fig. 21

Dust contamination along the suction side of the smooth blade and of the blade with ideal triangular riblets with a trapezoidal groove

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