Whistling of corrugated pipes
Citation for published version (APA):Tonon, D., Nakiboglu, G., Belfroid, S. P. C., Willems, J. F. H., & Hirschberg, A. (2009). Whistling of corrugated pipes. In Proceedings of 7th Euromech Solid Mechanics Conference, (ESMC7), 7-11 september, Lisbon
Document status and date: Published: 01/01/2009
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Whistling of corrugated pipes
Devis Tonon∗, G ¨unes¸ Nakibo˘glu∗, Stefan Belfroid†, Jan F.H.Willems∗, Avraham Hirschberg∗
∗Technische Universiteit Eindhoven
Department of Applied Physics, Fluid Dynamics Laboratory, PO. Box 513, 5600 MB Eindhoven, The Netherlands
d.tonon@tue.nl, g.nakiboglu@tue.nl, j.f.h.willems@tue.nl, a.hirschberg@tue.nl
†TNO Science and Industry
Delft, The Netherlands stefan.belfroid@tno.nl
ABSTRACT
Air flow through corrugated pipes can produce high sound levels. This whistling phe-nomenon, can lead to serious structural and environmental problems. Previous study [1] showed that a row of identical T-joints, forming a multiple side branch system is a reason-able model for corrugated pipes at low whistling frequencies. The current research is carried out to investigate the effect of various geometrical parameters (e.g. cavity width to cavity depth ratio, pipe diameter to pitch ratio) and operational parameters (e.g. system pressure). In this context several experiments have been carried out with different side branch geometries to characterize the whistling behavior of the system. In this paper the discussion is kept limited to the effect of cavity depth and edge shape on whistling frequency and pulsation amplitude.
The T-joints that have been used have an internal diameter (DP) of 33mm which is equal
to the inner diameter (Dsb) and depth (Lsb) of the the side branch. The length of the main pipe
(LP) of each T-joint is 100mm and the side branch is located half way along this segment.
Plugs with different heights were employed to vary the depth of the side branch segment. The multiple side branch system is connected to a high pressure air supply system. The acquisition system of the setup has been improved, compared to the one used earlier [1], by means of a trigger system which allows simultaneous measurement of the mean velocity from turbine flow meter and pressure from the piezo-electric pressure transducers placed at the end of the side branches.
Experiments performed with different number of T-joints showed that by increasing the number of side branches in the system a better representation of actual corrugated pipes can be achieved in the sense that even for high flow velocities the whistling frequencies corresponds to the longitudinal acoustic modes of the main pipe. The experiments presented in this study were performed with 19 side branches. A typical result that was obtained is shown in Figure 1
where the first 16thlongitudinal modes were detected.
To the authors’ knowledge, the work of the Binnie [2] on corrugated pipes is the first study which highlight the importance of cavity depth on whistling. He reported an increase of
Strouhal number from 0.4 to 0.7 when the ratio of pipe diameter to corrugation depth (Dp/Lsb)
is decreased. Later Belfroid [3] observed a similar increase in Strouhal number when
Flow Velocity [m/s] H e lm h o lt z N u m b e r -(f L / ceff ) 0 10 20 30 40 50 60 0 2 4 6 8
Figure 1: Measured Helmholtz number as a function of mean
flow velocity with 19 side branches and 8mm cavity depth
× × × × × × × × × × × × × × × × × × × × × × × × × × × × ×× × × × × × ×
Strouhal Number - SrWeff= fDsbπ/ 4U
D im e n s io n le s s p re s s u re fl u c tu a ti o n a m p li tu d e - p ’ / ( ρo co U ) 0.4 0.45 0.5 0.55 0.6 0.65 0 0.005 0.01 0.015 0.02 Lsb/ Dsb≈0.25 Lsb/ Dsb≈0.39 Lsb/ Dsb≈0.48 Lsb/ Dsb≈0.55 Lsb/ Dsb≈0.60 Lsb/ Dsb≈0.70 Lsb/ Dsb≈0.79 Lsb/ Dsb≈1.15 ×
Figure 2: Measured dimensionless pressure fluctuation
ampli-tude for the 2nd
acoustic mode as a function of Strouhal number
for corrugation and pipe volume, respectively. This effect is investigated for the multiple side branch system. Eight different side branch depths were considered ranging between 8mm and
38mm. The Strouhal number (SrW ef f = f Dsbπ/4U ) and respective dimensionless pressure
fluctuation amplitude (|p′| /ρ
0c0U ) for the 2ndacoustic mode is given in Figure 2. It is seen that
increasing cavity depth increases the amplitude of oscillations. A significant non-monotonous shift in Strouhal number is also observed with changing cavity depth. Between the depths
of 8mm and 13mm, which corresponds toLsb/Dsb ratio of approximately 0.25 and 0.39, an
increase in Strouhal number is observed with increasing cavity depth. However, for deeper
cav-ities (Lsb/Dsb from 0.39 to 1.15) a decrease in Strouhal number with increasing cavity depth
is observed. So the phenomenon is more complex than expected on the basis of data from the literature [2,3]. The effect of the edge shape of cavities has also been studied. As expected from the vortex sound theory [4] a rounded upstream edge result in a higher amplitude than a sharp one.
References
[1] G. Nakiboglu, S.P. Belfroid, D. Tonon, J.F.H. Willems, A. Hirschberg, “A parametric study on
the whistling of multiple side branch system as a model for corrugated pipes.”, Proceeding of
ASME Pressure Vessels and Piping Division Conference, Prague, 2009.
[2] A. M. Binnie, “Self induced waves in a conduit with corrugated walls II. Experiments with air in
corrugated and finned tubes.”, Proceedings of the Royal Society A 262, pp. 179-197, 1961.
[3] S.P. Belfroid, D. P. Shatto, R. M. Peters, “Flow induced pulsation caused by corrugated tubes.”, Proceeding of ASME Pressure Vessels and Piping Division Conference, San Antonio, 2007. [4] J. C. Bruggeman, A. Hirschberg, M. E. van Dongen, A. P. Wijnands, J. Gorter, “ Self-sustained
aero-acoustic pulsations in gas transport systems: experimental study of the influence of closed side branches.”, J. Sound and Vibration, 150, pp. 371-393, 1991.
