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Fundamental Issues and Canonical Flows

Flow Visualization and Frequency Characteristics of Velocity Fluctuations of Complex Turbulent Flow in a Short Elbow Piping Under High Reynolds Number Condition

[+] Author and Article Information
Hiroyuki Takamura1

 Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, 6-6-01-2, Aramaki-aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8579, Japanhtaka@karma.qse.tohoku.ac.jp

Shinji Ebara

 Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, 6-6-01-2, Aramaki-aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8579, Japanshinji.ebara@qse.tohoku.ac.jp

Hidetoshi Hashizume

 Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, 6-6-01-2, Aramaki-aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8579, Japanhidetoshi.hashizume@qse.tohoku.ac.jp

Kosuke Aizawa

 Advanced Nuclear System Research and Development Directorate, Japan Atomic Energy Agency, 4002 Narito-cho, Oarai, Ibaraki, 311-1393, Japanaizawa.kosuke@jaea.go.jp

Hidemasa Yamano

 Advanced Nuclear System Research and Development Directorate, Japan Atomic Energy Agency, 4002 Narito-cho, Oarai, Ibaraki, 311-1393, Japanyamano.hidemasa@jaea.go.jp

1

Corresponding author.

J. Fluids Eng 134(10), 101201 (Sep 28, 2012) (8 pages) doi:10.1115/1.4007436 History: Received January 25, 2012; Revised August 01, 2012; Published September 24, 2012; Online September 28, 2012

Flow visualization was performed on a single short elbow piping by means of two-dimensional particle image velocimetry. The piping was designed as a 1/7-scale model of a section of the cold-leg piping of a Japan sodium-cooled fast reactor. This study characterized the periodic motions and flow structures that appeared in and downstream of the elbow and potentially affected flow-induced vibrations. The flow field that related flow separation and frequency characteristics of the flow velocity fluctuation were explored for Reynolds number from 0.3 × 106 to 1.0 × 106 , which belonged to the post-critical regime. Experimental results show that flow structures are not strongly dependent on Reynolds number in this range. Frequency analysis for the velocity fluctuation in terms of Strouhal number (St) reveals that there exist not only two kinds of vortices with different shedding periods, but also one periodic flow in the circumferential direction. In the flow separation region, vortices are periodically emitted with St ≈ 0.5, while those with about 1.0 are shed in a shear flow region located between the separation region and the pipe center. Moreover, a periodic motion with St ≈ 0.5 appeared in the circumferential direction in the vicinity near the separation region. These values of St were not strongly dependent on Reynolds number in this study.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diagram of the experimental loop

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Figure 2

Visualization cross sections

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Figure 3

Coordinate system and viewpoints in the experiment: (a) Flow cross section and pipe cross section and (b) intrados cross section

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Figure 4

Mean flow velocity field at Re of 1.0 × 106

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Figure 5

Dependency of starting point and reattachment point of the flow separation on Re

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Figure 6

rms profiles of flow velocity fluctuation in the elbow downstream: (a) rms in the y direction and (b) rms in the x direction

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Figure 7

Time-averaged flow velocity field and rms distribution at y/D = 0 and 0.2. (a) Time-averaged flow field at y/D = 0. (b) Time-averaged flow field at y/D = 0.2. (c) rms values at y/D = 0 (left: r direction, right: φ direction). (d) rms values at y/D = 0.2 (left: r direction, right φ direction).

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Figure 8

Time-averaged flow velocity field at y/D = 0.2. (a) Time-averaged flow field for Re of 0.3 × 106 . (b) Time-averaged flow field for Re of 0.4 × 106 . (c) Time-averaged flow field for Re of 0.5 × 106 . (d) Time-averaged flow field for Re of 0.6 × 106 . (e) Time-averaged flow field for Re of 0.8 × 106 .

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Figure 9

Instantaneous flow velocity fields in the intrados cross section

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Figure 10

Locations of frequency analysis points

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Figure 11

Velocity fluctuation PSD profiles at point E in the shear flow region (x/D = 0.3, y/D = 0.2). (a) Velocity fluctuation in the y direction. (b) Velocity fluctuation in the x direction. (c) Velocity fluctuation in the φ direction.

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Figure 12

Velocity fluctuation PSD profiles at point B in the separated region (x/D = 0.05, y/D = 0.2). (a) Velocity fluctuation in the y direction. (b) Velocity fluctuation in the x direction. (c) Velocity fluctuation in the φ direction.

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Figure 13

Velocity fluctuation PSD profiles at point H in the extrados region (x/D = 0.9, y/D 0.2). (a) Velocity fluctuation in the y direction. (b) Velocity fluctuation in the x direction.

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Figure 14

Schematic drawing of the three coherent flow structures in a single elbow flow. (a) Vortices shedding in the shear flow region and its lower stream. (b) Vortices shedding in the separated region and its lower stream. (c) Circumferential flows opposite each other towards the intrados in the secondary flow.

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