Research Papers: Flows in Complex Systems

Experimental Investigation of Flow Field Structure in Mixing Tee

[+] Author and Article Information
Seyed Mohammad Hosseini

Department of Energy, Division of Fluid Mechanics, Lund University, Lund 22100, Swedenseyed_mohammad.hosseini@energy.lth.se

Kazuhisa Yuki, Hidetoshi Hashizume

Department of Quantum Science and Energy, Tohoku University, 6-6-01 Aza-Aoba, Aramaki, Sendai 980-8579, Japan

J. Fluids Eng 131(5), 051103 (Apr 13, 2009) (7 pages) doi:10.1115/1.3112383 History: Received February 13, 2008; Revised February 25, 2009; Published April 13, 2009

T-junction is one of the familiar components in the cooling system of power plants with enormous capability of high-cycle thermal fatigue. This research investigates the structure and mixing mechanism of turbulent flow in a T-junction area with a 90 deg bend upstream. According to the wide distribution of turbulent jets in the T-junction, a re-attached jet was selected previously as the best representative condition with the highest velocity fluctuation and the most complex structure. For considering the mixing mechanism of re-attached jet, T-junction is subdivided into few lateral and longitudinal sections, and each section is visualized separately by particle image velocimetry technique. Corresponding to the experimental data, the branch flow acts as a finite turbulent jet, develops the alternative type of eddies, and causes the high velocity fluctuation near the main pipe wall. Three regions are mainly subject to maximum velocity fluctuation: the region close to the jet boundaries (fluctuation mostly is caused by Kelvin–Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex), and the re-attached area (fluctuation mostly is caused by changing the pressure gradient in the wake area above the jet). Finally, the re-attached area (near the downstream of wake area above the jet) is introduced as a region with strongest possibility to high-cycle thermal fatigue with most effective velocity fluctuation on the main pipe wall above the branch nozzle.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Experimental apparatuses: (1) main pipe, (2) branch pipe, (3) tee junction, (4) 90 deg bend, (5) main pump, (6) branch pump, (7) heat exchanger, (8) heating tank, (9) mixing tank, (10) straightener tank, (11) measuring window, and (12) water jacket

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Figure 2

Flow field structure: (a) longitudinal section, parallel to the jet, (b) lateral section, and (c) longitudinal section, perpendicular to the jet; (1) initial part of the jet, (2) transitional part of the jet, (3) main part of the jet, (4) Kelvin–Helmholtz instability, (5) wake area, (6) secondary flow twin vortex, (7) high velocity area, (8) main flow turning area, (9) interface, (10) vortices act as Karman vortex, (11) large wake eddies, (12) moving cross section of the jet, (13) small eddies, (14) large eddies in the downstream, (15) main flow blow jet, and (16) small area below jet

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Figure 3

Positions of lateral and longitudinal sections to visualize the flow field

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Figure 4

Flow field in longitudinal section A: (a) average velocity distribution and (b) intensity of velocity fluctuation

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Figure 5

Average velocity distributions in different longitudinal sections

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Figure 6

Intensity of velocity fluctuation in different longitudinal sections

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Figure 7

Lateral section B: (a) average velocity vectors, (b) mean velocity distribution, and (c) intensity of velocity fluctuation

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Figure 8

Velocity vectors of time series and average flow field above the jet in C2 section (t=0.03 s, four continual frames, average of 240 frames, Ub=0.47 m/s, and Um=0.485 m/s)

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Figure 9

Five continual frames of time series data with close-up visualization (Ub=0.55 m/s and Um=0.73 m/s)

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Figure 10

Schematic of high velocity fluctuation areas near the main pipe wall in the T-junction area




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