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Research Papers

Leading Edge Jet Impingement Under High Rotation Numbers

[+] Author and Article Information
Cassius A. Elston

Department of Mechanical Engineering,
Baylor University,
Waco, TX 76798-7356

Lesley M. Wright

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

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received August 12, 2015; final manuscript received December 19, 2016; published online March 7, 2017. Assoc. Editor: Francis Kulacki.

J. Thermal Sci. Eng. Appl 9(2), 021010 (Mar 07, 2017) (12 pages) Paper No: TSEA-15-1221; doi: 10.1115/1.4035892 History: Received August 12, 2015; Revised December 19, 2016

The effect of rotation on jet impingement cooling is experimentally investigated in this study. Pressurized cooling air is supplied to a smooth, square channel in the radial outward direction. To model leading edge impingement in a gas turbine, jets are formed from a single row of discrete holes. The cooling air from the first pass is expelled through the holes, with the jets impinging on a semi-circular, concave surface. The inlet Reynolds number varied from 10,000 to 40,000 in the square supply channel. The rotation number and buoyancy parameter varied from 0 to 1.4 and 0 to 6.6 near the inlet of the channel, and as coolant is extracted for jet impingement, the rotation and buoyancy numbers can exceed 10 and 500 near the end of the passage. The average jet Reynolds number varied from 6000 to 24,000, and the jet rotation number varied from 0 to 0.13. For all test cases, the jet-to-jet spacing (s/djet = 4), the jet-to-target surface spacing (l/djet = 3.2), and the impingement surface diameter-to-diameter (D/djet = 6.4) were held constant. A steady-state technique was implemented to determine regionally averaged Nusselt numbers on the leading and trailing surfaces inside the supply channel and three spanwise locations on the concave target surface. It was observed that in all rotating test cases, the Nusselt numbers deviated from those measured in a nonrotating channel. The degree of separation between the leading and trailing surface increased with increasing rotation number. Near the inlet of the channel, heat transfer was dominated by entrance effects, however moving downstream, the local rotation number increased, and the effect of rotation was more pronounced. The effect of rotation on the target surface was most clearly seen in the absence of crossflow. With pure jet impingement, the deflection of the impinging jet combined with the rotation-induced secondary flows offered increased mixing within the impingement cavity and enhanced heat transfer. In the presence of strong crossflow of the spent air, the same level of heat transfer is measured in both the stationary and rotating channels.

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References

Figures

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Fig. 1

Typical cross section of a cooled turbine blade with leading edge impingement

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Fig. 2

Overview of rotating test facility (from Wright and Elston [42])

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Fig. 3

Leading edge impingement test section

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Fig. 4

Impingement jet plate details

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Fig. 5

Nusselt numbers in the stationary supply channel

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Fig. 6

Nusselt numbers on the stationary cylindrical target surface

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Fig. 7

Heat transfer enhancement in the rotating supply channel (Ω = 300 RPM)

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Fig. 8

Heat transfer enhancement in the rotating supply channel (ReDh,inlet = 20,000)

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Fig. 9

Effect of rotation number on heat transfer enhancement in the supply channel

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Fig. 10

Effect of buoyancy number on heat transfer enhancement in the supply channel

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Fig. 11

Heat transfer enhancement on the rotating target surface (Ω = 300 RPM)

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Fig. 12

Heat transfer enhancement on the rotating target surface (ReDh,inlet = 20,000, Rejet,avg = 12,000)

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Fig. 13

Effect of rotation number on heat transfer enhancement on the target surface

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Fig. 14

Effect of buoyancy number on heat transfer enhancement on the target surface

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