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RESEARCH PAPERS

Acoustic Excitation by Flow in T-Junctions

[+] Author and Article Information
S. Ziada

Department of Mechanical Engineering,  McMaster University, Hamilton, Ontario, Canadaziadas@mcmaster.ca

A. Scott1

Department of Mechanical Engineering,  McMaster University, Hamilton, Ontario, Canada

D. Arthurs

Department of Mechanical Engineering,  McMaster University, Hamilton, Ontario, Canada

1

Present address: Mechanical Engineering Department, University of Waterloo, Ontario, Canada.

J. Pressure Vessel Technol 129(1), 14-20 (Apr 15, 2006) (7 pages) doi:10.1115/1.2388995 History: Received August 03, 2005; Revised April 15, 2006

The flow-acoustic nature of sharp-edged T-junctions is investigated experimentally. In this paper, the pipes forming the T-crossbar are referred to as the branches and the pipe forming the central stem of the T-shape is referred to as the main pipe. Four test cases are studied corresponding to: (a) T-junction with flow from each branch into the main pipe; (b) T-junction with flow from one branch into the main pipe, the other branch being closed; (c) T-junction with flow from the main pipe into the two branches, which is the reverse flow situation of the first case; and (d) T-junction with flow from the main pipe into one branch and the other branch is closed, which is the second case with reverse flow. It is found that the flow at the T-junction can excite the pipe acoustic modes to varying degrees, depending on the flow direction and piping configuration. For cases (c) and (d), the dimensionless pressure amplitude of the acoustic mode reaches a maximum at a Strouhal number similar to that of the turbulence broadband peak measured in the separation bubble downstream of the T-junction corner. Cases (a) and (b) exhibit a different type of flow-acoustic coupling. In both cases, the maximum acoustic pressure occurs at a Strouhal number which is different from that observed in the separation bubble. In addition, the pulsation amplitude is substantially stronger than that observed in cases (c) and (d). Detuning the branches weakens the resonance intensity, especially in case (c), which exhibits the strongest acoustic resonance.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Possible flow patterns at T-junctions of piping systems

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Figure 2

Schematic presentation of test cases and mode shapes of the primary acoustic mode in the branch pipes. m indicates locations of microphone measurements and p indicates pitot tube locations.

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Figure 3

Schematic of the T-junction showing locations of pressure measurements in the separation bubble downstream of the sharp corners

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Figure 4

Typical pressure spectrum for case (c) measured at Vm=60m∕s. Measurement location is midway between the branch entrance and the T-junction as indicated by × in the insets.

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Figure 5

Typical pressure spectrum for case (a) measured at Vm=50m∕s. Measurement location is midway between the branch entrance and the T-junction as indicated by × in the inset.

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Figure 6

Typical pressure spectra for cases (a) and (c) showing the effect of flow direction on the acoustic response of various modes of the piping. Measurement location is midway between the branch entrance and the T-junction as indicated by × in the insets.

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Figure 7

Typical pressure spectra for cases (b) and (d) showing the effect of flow direction on the acoustic response of various modes of the piping. Measurement location is at the closed end of the branch as indicated by × in the insets.

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Figure 8

Normalized amplitude of the primary mode P*(fp1) for cases (a) and (c) as a function of the reduced velocity based on the primary mode frequency fp1

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Figure 9

Normalized amplitude of the primary mode P*(fp1) for cases (b) and (d) as a function of the reduced velocity based on the primary mode frequency fp1

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Figure 10

Power spectral density, ψ, and its normalized form, Φ, for case (d). Measurements were taken at x=0.45D for several flow velocities Vm in the range from 20to70m∕s.

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Figure 11

Normalized power spectral density, Φ, for case (a). Measurements were taken at x=0.60D for several flow velocities Vm in the range from 20to70m∕s.

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Figure 12

Pressure spectra measured at Vm=74m∕s for case (b). Spectrum 1: tuned branches without spacers; spectrum 2:2D spacer (Δ∕λ=1.9%); spectrum 3:4D spacer (Δ∕λ=3.5%); spectrum 4:6D spacer (Δ∕λ=5%); spectrum 5:8D spacer (Δ∕λ=6.4%).

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Figure 13

Effect of detuning the branches on the acoustic response of the primary mode in case (b). ▴, tuned branches without spacers; ◻, 2D spacer (Δ∕λ=1.9%); Δ, 4D spacer (Δλ=3.5%); ×, 6D spacer (Δλ=5%); ●, 8D spacer (Δλ=6.4%).

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Figure 14

Effect of detuning the branches on the acoustic response of the primary mode in case (a). ▴, tuned branches without spacers; Δ, 4D spacer (Δ∕λ=5.4%); ×, 6D spacer (Δ∕λ=7.8%); ●, 8D spacer (Δ∕λ=10%).

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