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Research Papers: Fundamental Issues and Canonical Flows

Effect of Initial Constant Acceleration on the Transition to Turbulence in Transient Circular Pipe Flow

[+] Author and Article Information
Manabu Iguchi, Yusuke Nakahata

Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, North 13, West 8, Kita-ku, Sapporo 060-8628, Japan

Kazuyoshi Nishihara

Graduate School of Engineering, Osaka Electro-Communication University, 18-8 Hatsu-cho, Neyagawa, Osaka 572-8630, Japan

Charles W. Knisely

Department of Mechanical Engineering, Bucknell University, Lewisburg, PA 17837

J. Fluids Eng 132(11), 111203 (Nov 09, 2010) (9 pages) doi:10.1115/1.4002519 History: Received March 26, 2010; Revised August 31, 2010; Published November 09, 2010; Online November 09, 2010

Experimental investigation is carried out on the transition to turbulence in a transient circular pipe flow. The flow is accelerated from rest at a constant acceleration until its cross-sectional mean velocity reaches a constant value. Accordingly, the history of the flow thus generated consists of the initial stage of constant acceleration and the following stage of constant cross-sectional mean velocity. The final Reynolds number based on the constant cross-sectional mean velocity and the pipe diameter is chosen to be much greater than the transition Reynolds number of a steady pipe flow of about 3000. The transition to turbulence is judged from the output signal of the axial velocity component and its root-mean-square value measured with a hot-wire anemometer. A turbulent slug appears after the cross-sectional mean velocity of the flow reaches the predetermined constant value under every experimental condition. Turbulence production therefore is suppressed, while the flow is accelerated. The time lag for the appearance of the turbulent slug after the cross-sectional mean velocity of the flow reaches the constant value decreases with an increase in the constant acceleration value. An empirical equation is proposed for estimating the time lag. The propagation velocity of the leading edge of the turbulent slug is independent of the constant acceleration value under the present experimental conditions.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 2

Experimental apparatus

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Figure 3

Schematic of programed cross-sectional mean velocity

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Figure 4

Schematic of axial velocity component accompanied by transition to turbulence

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Figure 5

Schematic diagram of cross-sectional mean velocities in constant acceleration flow and presently treated transient flow

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Figure 6

Output signals of the axial velocity component in constant acceleration flows at x/D=51.3

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Figure 7

Relationship between Retr and dimensionless acceleration R3a/ν2

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Figure 8

Output signals of axial velocity component (r/R=0.00, x/D=51.3)

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Figure 9

Output signals of axial velocity component (r/R=0.72, x/D=51.3)

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Figure 10

Output signals of axial velocity component (r/R=0.92, x/D=51.3)

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Figure 11

Measured cross-sectional mean velocities

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Figure 12

Comparison of programed and measured cross-sectional mean velocities (Acc. A, a=3.51 m/s2, a′=9.44×105, x/D=51.3)

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Figure 13

Comparison of measured value and analytical solution of axial velocity component (Acc. A, a=3.51 m/s2, a′=9.44×105, x/D=51.3)

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Figure 14

Comparison of programed and measured cross-sectional mean velocities (Acc. F, a=0.61 m/s2, a′=1.77×105, x/D=51.3)

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Figure 15

Comparison of measured value and analytical solution of axial velocity component (Acc. F, a=0.61 m/s2, a′=1.77×105, x/D=51.3)

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Figure 16

Radial distributions of axial velocity component around the initiation of turbulence

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Figure 17

Transition time values for Acc. A, Acc. E, and Acc. F (r/R=0.00 and 0.92)

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Figure 18

Mean transition time values for Acc. A, Acc. E, and Acc. F

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Figure 19

Schematic of a turbulent slug observed in this study

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Figure 20

Mean time lag values for Acc. A, Acc. E, and Acc. F

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Figure 21

Relationship between dimensionless time lag and dimensionless acceleration at x/D=51.3

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Figure 22

Correlation of mean time lag at x/D=51.3

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Figure 1

Three kinds of acceleration regimes

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