Experimental Investigation of the Acoustic Power Around Two Tandem Cylinders

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
S. L. Finnegan ◽  
C. Meskell ◽  
S. Ziada
Keyword(s):  
Flow Field ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Acoustic Resonance ◽  
Low Flow ◽  
Interaction Mechanisms ◽  
Tandem Cylinders ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Flow Velocities

Aeroacoustic resonance of bluff bodies exposed to cross flow can be problematic for many different engineering applications and knowledge of the location and interaction of acoustic sources is not well understood. Thus, an empirical investigation of the acoustically coupled flow around two tandem cylinders under two different resonant conditions is presented. It is assumed that the resonant acoustic field could be decoupled from the hydrodynamic flow field, resolved separately, and then recoupled to predict the flow/sound interaction mechanisms using Howe's theory of aerodynamic sound. Particle image velocimetry was employed to resolve the phase-averaged flow field characteristics around the cylinders at various phases in an acoustic wave cycle. It was found that the vortex shedding patterns of the two resonant conditions exhibit substantial differences. For the first condition, which occurred at low flow velocities where the natural vortex shedding frequency was below the acoustic resonance frequency, fully developed vortices formed in both the gap region between the cylinders and in the wake. These vortices were found to be in phase with each other. For the second resonant condition, which occurred at higher flow velocities where the natural vortex shedding frequency was above the acoustic resonant frequency, fully developed vortices only formed in the wake and shedding from the two cylinders were not in phase. These differences in the flow field resulted in substantial variation in the flow-acoustic interaction mechanisms between the two resonant conditions. Corresponding patterns of the net acoustic energy suggest that acoustic resonance at the lower flow velocity is due to a combination of shear layer instability in the gap and vortex shedding in the wake, while acoustic resonance at the higher flow velocity is driven by the vortex shedding in the wake of the two cylinders.

Numerical Simulation of the Flow-Sound Interaction Mechanisms of a Single and Two-Tandem Cylinders in Cross-Flow

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
A. Mohany ◽  
S. Ziada
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Positive Energy ◽  
Single Cylinder ◽  
Interaction Mechanisms ◽  
Tandem Cylinders

A numerical simulation of the flow-excited acoustic resonance for the case of two-tandem cylinders in cross-flow is performed. The spacing ratio between the cylinders (L/D=2.5) is inside the proximity interference region. Similar simulation is performed for the case of a single cylinder. The unsteady flow field is simulated using a finite-volume method. This simulation is then coupled with a finite-element simulation of the resonant sound field, by means of Howe’s theory of aerodynamics sound, to reveal the details of flow-sound interaction mechanisms, including the nature and the locations of the aeroacoustic sources in the flow field. For the case of a single cylinder, acoustic resonance is excited over a single range of flow velocity. The main aeroacoustic source, which causes a positive energy transfer from the flow field to the acoustic field, is found to be located just downstream of the cylinder. For the case of two-tandem cylinders, the acoustic resonance is excited over two different ranges of flow velocity: the precoincidence and the coincidence resonance ranges. For the coincidence resonance range, the main aeroacoustic source is found to be located just downstream of the downstream cylinder, and the excitation mechanism of this resonance range is found to be similar to that of a single cylinder. However, for the precoincidence resonance range, the primary acoustic source is found to be located in the gap between the cylinders. Moreover, flow visualization of the wake structure for the two-tandem cylinders during acoustic resonance shows that for the precoincidence resonance range there is a phase shift of about 90 deg between the vortex shedding from the upstream and the downstream cylinders, which is different from the coincidence resonance range, where the vortex shedding from both cylinders seems to be in-phase.

Applicability of The Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders In Cross-Flow

2021 ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Interaction Mechanism ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Effective Diameter ◽  
Finned Tubes ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Abstract This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each type of fins, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

In-Situ Measurement of Thermowell Vibration During Production Train Pressurization

2002 ◽  
Author(s):  
Paul N. Finch ◽  
Michael G. Hamblin ◽  
Damien C. Constable
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Vibration Measurement ◽  
Start Up ◽  
Form Part ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Mechanism Of Failure ◽  
Flow Velocities

Fatigue failure of intrusive fittings such as erosion probes, sample quills and thermowells, has occurred in Woodside’s offshore and onshore operations. The mechanism of failure is generally thought to be resonant vibration caused by vortex shedding. The consequence of these failures can be severe, in particular for thermowells, as they form part of the pressure envelope, and hydrocarbon release can result. Thermowells on the Goodwyn Alpha platform flow lines were designed to withstand the maximum normal operating flow velocities. During production train pressurisation, however, the thermowells can experience velocities higher than the design limit, albeit for a limited time. These start up flow velocities are likely to cause vortex shedding frequencies exceeding flowline thermowell resonant frequencies. If a vortex shedding frequency occurs that is close to a thermowell natural frequency, a vortex “lock on” resonance can occur, resulting in large amplitude thermowell vibration transverse to the flow direction. In order to determine if thermowell replacement was warranted, a study was undertaken to measure the thermowells in situ. The specific aims were: to determine if vortex “lock on” was occurring; and to determine what cyclic stresses are present. To do this, a novel vibration measurement probe was developed and commissioned. The probe is capable of measuring bidirectional acceleration in thermowells without the need for the thermowell to be taken offline. This paper presents the development of the probe and the results of the measurements during flowline pressurisation.

Synchronization Characteristics of Vortex Shedding From Tube Banks on Acoustic Resonance

2013 ◽  
Author(s):  
Hiromitsu Hamakawa ◽  
Eiichi Nishida ◽  
Kenta Asakura
Keyword(s):  
Vortex Shedding ◽  
Pressure Fluctuation ◽  
Acoustic Pressure ◽  
Broad Band ◽  
Acoustic Resonance ◽  
Modeling Method ◽  
Acoustic Damping ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Tube Banks

In the present paper the attention is focused on vortex shedding synchronization on acoustic resonance in in-line tube banks which occurred in the two-dimensional model of boiler. And we have examined the verification of proposed modeling method. We measured the characteristics of acoustic resonance, acoustic damping, the pressure fluctuation on the surface of tubes at the nodes of acoustic pressure and the acoustic pressure fluctuation on the side wall of the duct. As the acoustic mode number increased, the acoustic damping ratio decreased. As the tube pitch ratio in the flow direction decreased, the acoustic damping increased for all acoustic modes and the vortex shedding frequency became broad-band. The multiple resonance modes of lower acoustic damping were generated within the broad-band vortex shedding frequency. If the acoustic resonance occurred, the peak level of spectrum of surface pressure fluctuation and the coherence between vortex shedding and wall acoustic pressure in the tube banks also increased. The features of experimental results agree well with those obtained by using the proposed modeling method. We have discussed the characteristics of vortex shedding synchronization by using proposed the modeling method.

DEVELOPMENT OF ROBUST VELOCIMETER FOR NATURAL WATER FLOW MONITORING

2016 ◽  
Vol 78 (7) ◽  
Author(s):  
Masataka Shirakashi ◽  
Kye Wei Yeo ◽  
Mizuyasu Koide ◽  
Tsutomu Takahashi ◽  
Sheikh Ahmad Zaki Shaikh Salim
Keyword(s):  
Flow Velocity ◽  
Water Flow ◽  
Vortex Shedding ◽  
Natural Water ◽  
Dominant Frequency ◽  
Hot Wire ◽  
Flow Monitoring ◽  
University Of Technology ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The ring-velocimeter coupled with a hot wire/film probe was developed and has been applied to wind and water tunnel experiments in Fluids Engineering Laboratory of Nagaoka University of Technology.  In this study, the hot-wire/film probe is replaced by a cantilever attached by a strain gauge to detect the drag acting on the ring.  The vortex shedding frequency from the ring is determined from the drag fluctuation by applying the spectrum analysis, and the flow velocity in turn since it is proportional with the vortex shedding frequency.  This technique for flow velocity measurement is robust in the sense that it is strong against the noise or decay of the detected signal since the dominant frequency is insensitive to such disturbances, and that the detecting probe is strong against the contaminants or particles/objects carried by the fluid.  These advantages, together with its simple and cheap characteristics, make it possible to apply to natural water flow with severe conditions.

Equivalent Diameter for Predicting Vortex Shedding of Finned Cylinders in Cross-Flow

2021 ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Vortex Shedding ◽  
Tube Bundle ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Finned Tube ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Frequency Scaling ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Abstract This article explores different equivalent diameter equations found in the literature for shedding frequency scaling and applying it to various types of finned cylinders in industrial heat exchangers. The focus is on three finned cylinder types: straight, twist-serrated, and crimped spirally finned cylinders. Within each finned cylinder category, at least three different finned cylinders are investigated. The results indicate that utilizing the appropriate equivalent diameter for vortex shedding frequency scaling collapses the data within the Strouhal bounds of a bare cylinder away from resonance excitation. However, the onset of flow-excited acoustic resonance and peak acoustic pressure in all the finned cylinder cases occur at a reduced flow velocity earlier than their equivalent diameter bare cylinder. This suggests that although utilizing the appropriate equivalent diameter can predict the shedding frequency away from resonance, it cannot be used in velocity scaling to predict the onset of acoustic resonance in finned tube bundle.

Numerical Simulation of the Flow-Sound Interaction Mechanisms of Two Side-by-Side Cylinders in Cross-Flow

2011 ◽  
Author(s):  
Atef Mohany ◽  
Marwan Hassan ◽  
Samir Ziada
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Single Frequency ◽  
Interaction Mechanisms ◽  
Spacing Ratio ◽  
Volume Method

A numerical simulation of the flow-excited acoustic resonance for the case of two side-by-side cylinders in cross-flow is performed. One spacing ratio between the cylinders, T/D = 1.25, is investigated, where D is the diameter of the cylinders and T is the center-to-center distance between them. The unsteady flow field is simulated using a finite-volume method at a Reynolds number of 25000. This simulation is then coupled with a finite element simulation of the resonant sound field, by means of Howe’s theory of aerodynamics sound, to reveal the details of flow-sound interaction mechanisms, including the nature and the locations of the aeroacoustic sources in the flow field. At the off resonance conditions two distinct vortex shedding frequencies are observed. These are associated with the wider and narrower wakes of the cylinders. However, when acoustic resonance is initiated the bi-stable flow phenomenon is eliminated and the vortex shedding from both cylinders occurs at a single frequency that is between those observed before the onset of acoustic resonance. Moreover, three main aeroacoustic sources are observed in the wake of the two cylinders. Two aeroacoustic sources are located just downstream of each cylinder and one aeroacoustic source is located in the gap between the cylinders. The numerical results are compared with the experimental results presented in a previous investigation and favourable agreement is obtained.

Aeroacoustic Source Distribution Around Four Cylinders Orientated in a Square

2010 ◽  
Author(s):  
Shane Leslie Finnegan ◽  
Craig Meskell ◽  
Peter Oshkai
Keyword(s):  
Flow Field ◽  
Vortex Shedding ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Pressure Level ◽  
Field Conditions ◽  
Acoustic Sources ◽  
Four Cylinders ◽  
Flow Velocities

An experimental investigation of the flow-acoustic coupling of four cylinders arranged in a square configuration with a spacing ratio in the proximity interference range subject to forced acoustic resonance is presented. The aeroacoustic characteristics and the flow field structures are investigated at various sound pressure levels to study its influence on the “lock-in” behaviour of the separated flow and the corresponding distribution of the resonant acoustic sources. Two mainstream flow velocities were selected for testing that corresponded to flow field conditions before acoustic-Strouhal coincidence of the vortex shedding frequency with the natural acoustic frequency of the duct and to flow field conditions after acoustic-Strouhal coincidence. Increasing the sound pressure level was found to slightly increase the range of flow velocities with which the acoustics could entrain the vortex shedding regime. Increasing the sound pressure level was also found to shorten the length of the most intense vortical structures in the shear layers emanating from the upstream cylinders and hence also shifted the dominant acoustic sources upstream. Spatial distributions of the net acoustic energy suggests that the mechanism triggering acoustic resonance of the four cylinders is shear layer instability, which is similar to that observed for two tandem cylinders.

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 70-78 ◽  
Author(s):  
A. J. Grass ◽  
P. W. J. Raven ◽  
R. J. Stuart ◽  
J. A. Bray
Keyword(s):  
Boundary Layer ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Combined Effects ◽  
Maximum Increase ◽  
Velocity Gradients ◽  
Large Velocity ◽  
Layer Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

An Experimental Study on the Vertical Flow Past a Finite-Length Horizontal Cylinder at Low Reynolds Numbers

2014 ◽  
Vol 493 ◽  
pp. 68-73 ◽  
Author(s):  
Willy Stevanus ◽  
Yi Jiun Peter Lin
Keyword(s):  
Finite Length ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortex Street ◽  
Vertical Flow ◽  
Low Reynolds Numbers ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (ReD) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for ReD = 250, but as the ReD increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

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