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Research Papers

The Effects of Ribs and Tip Wall Distance on Heat Transfer for a Varying Aspect Ratio Two-Pass Ribbed Internal Cooling Channel

[+] Author and Article Information
Sean C. Jenkins

e-mail: sean.jenkins@itlr.uni-stuttgart.de

Bernhard Weigand

Institut für Thermodynamik der Luft- und Raumfahrt,
Universität Stuttgart,
Pfaffenwaldring 31,
70569 Stuttgart, Germany

Martin Schnieder

ALSTOM,
Brown Boveri Strasse 7,
5401 Baden, Switzerland

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNALOF TURBOMACHINERY. Manuscript received January 26, 2009; final manuscript received October 20, 2011; published online October 31, 2012. Editor: David Wisler.

J. Turbomach 135(2), 021001 (Oct 31, 2012) (9 pages) Paper No: TURBO-09-1010; doi: 10.1115/1.4006584 History: Received January 26, 2009; Revised October 20, 2011

Internal cooling channels with differing aspect ratios are typically found in gas turbine blades due to the varying thickness of the blade from the leading to trailing edge. These serpentine passages often contain several 180 deg bends, which are sharp edged in the region of the blade tip. The 180 deg bend has a pronounced effect on the heat transfer characteristics in the outlet channel and tip wall, where a strong influence is seen due to the divider wall-to-tip wall distance in the bend. The present study investigates the effect of the divider wall-to-tip wall distance for a ribbed two-pass cooling channel with a 2:1 inlet and 1:1 outlet channel. Spatially resolved heat transfer measurements were made using the transient thermochromic liquid crystal technique for a smooth and a ribbed configuration using parallel 45 deg ribs. Effects of the 180 deg bend on heat transfer and rib-induced enhancements were identified separately and bend effects were found to dominate the heat transfer increase in the outlet channel near the bend. Pressure losses due to the bend and ribs were also independently evaluated for a range of tip wall distances. Results show that the smaller tip wall distances increase heat transfer on the tip wall and outlet channel but at the cost of an increased pressure loss. An optimum tip wall position is suggested, forming a compromise between heat transfer improvement and increased pressure losses.

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Figures

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Fig. 1

Schematic top view and cross section of the test channel with and without 45 deg ribs

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Fig. 2

Diagram of test rig

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Fig. 3

Nusselt number distributions normalized by the Dittus–Boelter relation for smooth channel, Re = 100,000

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Fig. 4

Left: Nusselt number distribution for smooth channel indicating regions for area averages; right: area averages for smooth channel normalized by Dittus–Boelter relation

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Fig. 5

Left: Nusselt number distribution for smooth channel normalized by average Nusselt number in inlet smooth H/W = 2:1 channel (NuSm); right: area averages for smooth channel normalized by NuSm

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Fig. 6

Nusselt number distributions for 45 deg ribbed channel normalized by inlet smooth channel average

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Fig. 7

Distributions of rib-related enhancement of Nusselt number for the ribbed channel by point-wise normalization by smooth channel results

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Fig. 8

Effect of variation of divider wall-to-tip wall distance for Wel/Wavg = 0.67, 1.0, and 1.33 with 45 deg ribs on top ribbed wall

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Fig. 9

Effect of variation of divider wall-to-tip wall distance for Wel/Wavg = 0.67, 1.0, and 1.33 with 45 deg ribs on inlet, tip wall, and outlet walls

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Fig. 10

Rib segment averages for the ribbed top wall for tip wall distances, Wel/Wavg = 0.67, 1.0, and 1.33

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Fig. 11

Rib segment averages for the unribbed inlet and outlet for tip wall distances, Wel/Wavg = 0.67, 1.0, and 1.33

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Fig. 12

Variation in normalized pressure loss due to the bend for a range of tip wall distances from Wel/Wavg = 0.67, to 1.33 for the channel with 45 deg ribs

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