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Research Papers

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

[+] Author and Article Information
Lesley M. Wright

e-mail: Lesley_Wright@Baylor.edu
Department of Mechanical Engineering
Baylor University
Waco, TX 76798-7356

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 31, 2011; final manuscript received August 20, 2011; published online October 30, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011028 (Oct 30, 2012) (10 pages) Paper No: TURBO-11-1169; doi: 10.1115/1.4006422 History: Received July 31, 2011; Revised August 20, 2011

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

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Figures

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Fig. 1

TSP calibration curve

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Fig. 2

Overview of experimental setup

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Fig. 3

Dimple roughened channel details

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Fig. 4

V-shaped dimple details

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Fig. 5

Detailed Nusselt number ratio distributions from TLC ((a)–(d)) and TSP ((e)–(h))

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Fig. 6

Detailed Nusselt number ratios from TLC

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Fig. 7

Conceptual view of V-shaped dimple induced secondary flow

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Fig. 8

Centerline Nusselt number distributions

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Fig. 9

Spanwise Nusselt number ratio distributions at trailing edge of V-shaped dimple

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Fig. 10

Effect of streamwise location on the spanwise Nusselt number ratio

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Fig. 11

Comparison of transient TLC and TSP techniques

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Fig. 12

Average Nusselt number ratio comparison with previous studies

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Fig. 13

Friction factor ratio comparison with previous studies

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Fig. 14

Thermal performance comparison with previous studies

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