Flow-excited Acoustic Resonance Research Articles

Flow-Induced Acoustic Resonance of Finned Cylinders With Varying Fin Heights

Abstract The flow-excited acoustic resonance phenomenon, which is instigated by periodic flow perturbation, leads to the generation of acute sound pressure. In this work, we investigated the characteristics of the flow-excited acoustic resonance for circular finned cylinders with different fin heights. The fin height is expressed as a normalized form considering the ratio of the fin diameter to the root cylinder diameter. The experiments are performed with finned cylinders having a range of diameter ratios between 1.5<Df/Dr<2.5. The diameter ratios are varied by changing the root diameter and fin diameter separately as well as simultaneously while keeping the fin pitch and the fin thickness constant. The results show that the excitation of acoustic resonance has profound dependence on the diameter ratio. Increasing the diameter ratios of the finned cylinder results in strong acoustic resonance excitation. The lock-in width and the onset of the acoustic resonance excitation also depend on the diameter ratio of the cylinders. Moreover, the results show that using an effective diameter based on the geometrical flow blockage does not take into account the changes occurring in the source of resonance excitation due to the addition of fins.

Passive noise control technique for suppressing acoustic resonance excitation of spirally finned cylinders in cross-flow

This paper presents an innovative passive noise control technique for suppressing flow-excited acoustic resonance of spirally finned cylinders in cross-flow. This was achieved by maintaining the number of fins, but varying the fin density along the finned cylinder’s span to create a non-uniform finned cylinder. Two non-uniform finned cylinders were investigated with pitch ratios of p(mid)/p(side) = 0.5 and 1.7. To better understand the influence of the non-uniform finned cylinders on the wake structure, bare cylinders with the same effective diameter were investigated. In the non-uniform finned cylinder case, due to the variation in the fin density, the effective diameter along its span changes. Thus, the effective diameter of a non-uniform finned cylinder happens to be a dual diameter cylinder. Three dual diameter cylinders were investigated with diameter ratios ranging between 0.5 ≤ D(mid)/D(side) ≤ 2. These diameter ratios closely correspond to the pitch ratio (p(mid)/p(side)) and effective diameter ratio (Dc(mid)/Dc(side)) of the non-uniform finned cylinders investigated. The results show that the non-uniform finned cylinderscause spatial variations in the vortex shedding process due to dissimilarities in the flow behavior at different fin density regions. Temporal variations were also revealed due to changes in the vortex shedding frequency at different spanwise regions. This resulted in a significant decrease in the spanwise flow coherence and vortex shedding strength. The spatio-temporal variations in the shed vortices at different spanwise regions observed by the non-uniform finned cylinders were found to be analogous to dual diameter cylinders with diameter ratios equivalent to the pitch ratios of the non-uniform finned cylinder. As a result, substantial attenuation in the acoustic pressure during flow-excited acoustic resonance was achieved by the non-uniform finned cylinders. The results presented in this paper show that non-uniform finned cylinders are a viable noise control technique for suppressing flow-excited acoustic resonance in tube bundles of heat exchangers.

Near-Wake Characteristics and Acoustic Resonance Excitation of Crimped Spirally Finned Cylinders in Cross-Flow

This paper presents an experimental investigation of the near-wake flow characteristics for isolated crimped spirally finned cylinders in cross-flow and its influence on the generated sound pressure during flow-excited acoustic resonance. Four crimped spirally finned cylinders are investigated, which have pitch-to-root diameter ratio (p/Dr) ranging between 0.384 ≤ p/Dr ≤ 1. A new equivalent diameter equation (Dc) has been developed to better capture the vortex shedding frequency emanating from the crimped spirally finned cylinders. The addition of crimped spiral fins reduces the coherence of the vortex shedding process as compared to that of a bare cylinder. Moreover, the addition of crimped spiral fins causes an elongation in the vortex formation region, as well as induces a larger velocity deficit in the near-wake. Reduction in the pitch-to-diameter ratio (p/Dr) leads to a progressive increase in the strength and coherence of the vortex shedding process. It also results in a gradual reduction in the vortex formation length and velocity deficit. The near-wake flow characteristics of the crimped spirally finned cylinders inherently affect the sound pressure during flow-excited acoustic resonance. Furthermore, the helical fins impose an asymmetrical inclination of the acoustic particle velocity. This hinders the flow-acoustic coupling, leading to a weakened energy transfer between the flow and sound fields. The findings of this investigation provide better understanding of the complex flow-sound interaction mechanism from crimped spirally finned cylinders in heat exchanger tube bundle.

Effect of impingement edge geometry on the acoustic resonance excitation and Strouhal numbers in a ducted shallow cavity

Flow-excited acoustic resonance in ducted cavities can produce high levels of acoustic pressure that may lead to severe damage. This occurs when the flow instability over the cavity mouth, which is created by the free shear layer separation at the upstream edge, is coupled with one of the acoustic modes in the accommodating enclosure. Acoustic resonance can cause high amplitude fluctuating acoustic loads in and near the cavity. Such acoustic loads could cause damage in sensitive applications such as aircraft weapon bays. Therefore, the suppression and mitigation of these resonances are very important. Much of the work done in the past focused on the fluid-dynamic oscillation mechanism or suppressing the resonance by altering the edge condition at the shear layer separation. However, the effect of the downstream edge has received much less attention. This paper considers the effect of the impingement edge geometry on the acoustic resonance excitation and Strouhal number values of the flow instabilities in a ducted shallow cavity with an aspect ratio of 1.0. Several edges, including chamfered edges with different angles and round edges with different radii, were investigated. In addition, some downstream edges that have never been studied before, such as saw-tooth edges, spanwise cylinders, higher and lower steps, and straight and delta spoilers, are investigated. The experiments are conducted in an open-loop wind tunnel that can generate flows with a Mach number up to 0.45. The study shows that when some edge geometries, such as lower steps, chamfered, round, and saw-tooth edges, are installed downstream, they demonstrate a promising reduction in the acoustic resonance. On the other hand, higher steps and straight spoilers resulted in intensifying the acoustic resonance. In addition, the effect of edge geometry on the Strouhal number is presented.

The effect of upstream edge geometry on the acoustic resonance excitation in shallow rectangular cavities

The flow-excited acoustic resonance phenomenon is created when the flow instability oscillations are coupled with one of the acoustic modes of a confined duct, which in turn generates acute noise problems and/or excessive vibrations. In this study, the effect of the upstream edge geometry on attenuating these undesirable effects is investigated experimentally for flows over shallow rectangular cavities with two different aspect ratios of L/D = 1 and 1.67, where L is the cavity length and D is the cavity depth, for Mach number up to 0.45. The acoustic resonance modes of the cavity are self-excited due to the development of free shear layers over the cavity mouth. Twenty four different upstream cavity edges are investigated in this study, including round edges, chamfered edges, vortex generators, and spoilers with different sizes and configurations. The results for each upstream cavity edge are compared with the base case where sharp edge is used. Most of the spoiler edges are found to be effective in suppressing the pressure amplitude of the excited acoustic resonance. Hot-wire measurements that were taken along the lateral direction downstream of the spoilers reveal the existence of secondary vortices generated by the spoilers, orthogonal to the cavity shear layer, which results in suppressing the resonance. The performance of each spoiler depends on its specific geometry (i.e. thickness, height, and angle) and the size and strength of the orthogonal vortices that can be generated. A summary of the results is presented in this paper.

Flow-Excited Acoustic Resonance of Trapped Modes of a Ducted Rectangular Cavity

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly and Ziada (2010, “Flow-Excited Resonance of Trapped Modes of Ducted Shallow Cavities,” J. Fluids Struct., 26(1), pp. 92–120; 2011, “Azimuthal Behaviour of Flow-Excited Diametral Modes of Internal Shallow Cavities,” J. Sound Vib., 330(15), pp. 3666–3683; and 2012, “Effect of Mean Flow on the Trapped Modes of Internal Cavities,” J. Fluids Struct., 33, pp. 70–84) investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.

Flow-induced vibrations in closed side branch pipes and their attenuation methods

Some problems due to flow-induced vibrations related to closed side branch pipes have been observed in thermal and nuclear power plants. Fluctuating pressure generated in the main pipes was unusually, acoustically excited in closed side branch pipes, and intense vibrations were caused at pipes and components. For example, flow-excited acoustic resonance in closed side branches of stub pipes of safety relief valves caused the failure of steam dryers in the United States Quad City Unit 2 nuclear power plant. Furthermore, there was a possibility that residual air or gas in a closed side branch pipe unexpectedly caused severe vibrations of low frequency in the feed water piping system. We have investigated the root cause and influence of air on severe vibrations. Intense fluctuating pressure was often caused by water hammer due to valve closure and it became larger in the closed side branch pipes. We showed that an additional side branch with an orifice was very effective to suppress the flow-induced acoustic resonance. Design methods of the orifice to attenuate fluctuating pressure generated by water hammer were presented considering Mach number, the pressure loss coefficient of orifice and the intensity of particle velocity. Moreover, suitability of the characteristic curve method was confirmed for evaluation of the attenuation effect of an orifice on fluctuating pressure generated by water hammer. Finally, we considered some flow-induced vibration problems related to closed side branch pipes and their attenuation methods.

Flow-Excited Acoustic Resonance of Isolated Cylinders in Cross-Flow

The flow-excited acoustic resonance of isolated cylinders in cross-flow is investigated experimentally where the effect of the cylinder(s) proximity to the acoustic particle velocity nodes of the cross-modes is presented in this paper. For the case of a single cylinder, the cylinder's location does not significantly affect the vortex shedding process; however, it affects the excitation level of each acoustic cross-mode. When the cylinder is moved away from the acoustic particle velocity antinode of a specific acoustic cross-mode, a combination of the cross-modes is excited with intensities that seem to be proportional to the ratio of the acoustic particle velocities of these modes at the cylinder's location. For the cases of two and three hydrodynamically uncoupled cylinders positioned simultaneously side-by-side in the duct, it is observed that the first three acoustic cross-modes are excited. When one cylinder is positioned at the acoustic particle velocity antinode of a specific cross-mode and another cylinder is positioned at its acoustic particle velocity node, i.e., a cylinder that should excite the resonance and another one that should not excite it, respectively; the excitation always takes over and the resonance occurs at a further elevated levels. It is also observed that the acoustic pressure levels in the cases of multiple cylinders are not resulting from a linear superposition of the excited level obtained from each individual cylinder which indicates that the removal of cylinders at certain locations may not be a viable technique to eliminate the acoustic resonance in the case of tube bundles.

Flow-excited acoustic resonance of a Helmholtz resonator: Discrete vortex model compared to experiments

The acoustic resonance in a Helmholtz resonator excited by a low Mach number grazing flow is studied theoretically. The nonlinear numerical model is established by coupling the vortical motion at the cavity opening with the cavity acoustic mode through an explicit force balancing relation between the two sides of the opening. The vortical motion is modeled in the potential flow framework, in which the oscillating motion of the thin shear layer is described by an array of convected point vortices, and the unsteady vortex shedding is determined by the Kutta condition. The cavity acoustic mode is obtained from the one-dimensional acoustic propagation model, the time-domain equivalent of which is given by means of a broadband time-domain impedance model. The acoustic resistances due to radiation and viscous loss at the opening are also taken into account. The physical processes of the self-excited oscillations, at both resonance and off-resonance states, are simulated directly in the time domain. Results show that the shear layer exhibits a weak flapping motion at the off-resonance state, whereas it rolls up into large-scale vortex cores when resonances occur. Single and dual-vortex patterns are observed corresponding to the first and second hydrodynamic modes. The simulation also reveals different trajectories of the two vortices across the opening when the first and second hydrodynamic modes co-exist. The strong modulation of the shed vorticity by the acoustic feedback at the resonance state is demonstrated. The model overestimates the pressure pulsation amplitude by a factor 2, which is expected to be due to the turbulence of the flow which is not taken into account. The model neglects vortex shedding at the downstream and side edges of the cavity. This will also result in an overestimation of the pulsation amplitude.

Passive control of flow-excited acoustic resonance in rectangular cavities using upstream mounted blocks

A passive method for controlling the flow-excited acoustic resonance resulting from subsonic flows over rectangular cavities in channels is investigated. A cavity with length to depth ratio of \(L/D=1\) is tested in air flow of Mach number up to 0.45. When the acoustic resonance is excited, the sound pressure level in the cavity reaches 162 dB. Square blocks are attached to the surface of the channel and centred upstream of the cavity leading edge to suppress the flow-excited acoustic resonance in the cavity. Six blocks of different widths are tested at three different upstream distances. The results show that significant attenuation of up to 30 dB of the excited sound pressure level is achieved using a block with a width to height ratio of 3, while blocks that fill the whole width of the channel amplify the pressure of the excited acoustic resonance. Moreover, it is found that placing the block upstream of the cavity causes the onset of the acoustic resonance to occur at higher flow velocities. In order to investigate the nature of the interactions that lead to suppression of the acoustic resonance and to identify the changes in flow patterns due to the placement of the block, 2D measurements of turbulence intensity in the shear layer and the block wake region are performed. The location of the flow reattachment point downstream of the block relative to the shear layer separation point has a major influence on the suppression level of the excited acoustic resonance. Furthermore, higher attenuation of noise is related to lower span-wise correlation of the shear-layer perturbation.

Visualization study of flow-excited acoustic resonance in closed tandem side branches using high time-resolved particle image velocimetry

Flow-induced acoustic resonance in a piping system containing closed tandem side branches was investigated experimentally. Velocity perturbation was induced at the mouth of a cavity by using two pumps and a block. An unusual acoustic mode change from a higher to a lower mode was observed when the flow rate in the main pipe increased. This phenomenon was examined by high time-resolved particle image velocimetry (PIV). It was found that fluid flows at different points in the cavity have some phase differences between them and that they interact with each other. The relationship between the fluid flows was clarified and the phase difference between the acoustic pressure fluctuations at different points in the cavity was obtained. Using these data, the phase delays of oscillations at different points were two-dimensionally mapped. This two-dimensional phase map was helpful in clarifying the feedback mechanism of self-induced vibrations.

Flow-Sound Interaction Mechanisms in the Wake of Two Side-By-Side Cylinders

The phenomenon of flow-excited acoustic resonance, where periodic flow oscillations are enhanced by a resonant sound field, is a design concern in many engineering applications such as in heat exchangers, piping systems, and cavity flows. This study experimentally examines the phenomenon of flow-excited acoustic resonance for two side-by-side cylinders in a duct with cross-flow. This geometry has been investigated for three cylinder spacing ratios, defined as the center-to-center distance between the cylinders normalized by their diameter, of T/D = 1.25, 1.46 and 2.5, and for a range of acoustic pressure amplitudes. Intermediate and small spacing ratios have been given special attention, as these cases have been found to exhibit bistable flow in the wake in the absence of acoustic resonance. Phase-locked PIV measurements reveal that the self-excited sound field produces a strong oscillatory flow pattern in the cylinder wakes, which is symmetric for large spacing ratios and high acoustic amplitudes, but remains bistable for small spacing ratios, even during very intense acoustic resonances. The aeroacoustic sources and sinks within the flow field, computed using Howe's theory of vortex sound, are compared for the range of spacing ratios and acoustic pressure amplitudes examined in this study.

AEROACOUSTIC RESPONSE OF ISOLATED CYLINDER(S) IN CROSS-FLOW AT DIFFERENT LOCATIONS INSIDE A RECTANGULAR DUCT

ABSTRACT: The flow-excited acoustic resonance of single and multiple isolated cylinders in cross-flow is investigated experimentally. The effect of the cylinder(s) proximity to the acoustic particle velocity nodes of the first three acoustic cross-modes is presented. During the experiments, the acoustic cross-modes of the duct hosing the cylinders are self-excited. For the case of single cylinder, it is observed that although the cylinder′s location doesn′t significantly affect the process of vortex shedding, it affects the mechanism of the flow-excited acoustic resonance and the generated acoustic pressure. When the cylinder is shifted away from the acoustic particle velocity anti-node of a certain acoustic cross-mode, a combination of cross-modes is excited with intensities that seem to be proportional to the ratio of the acoustic particles velocities of these modes at the cylinder′s location. For the case of two and three isolated cylinders positioned simultaneously side-by-side in the duct, it is observed that when the cylinders are positioned at different acoustic particle velocity anti-nodes of different cross-modes, the intensities of the excited acoustic resonance of these cross-modes are amplified compared to those with single cylinder. Nevertheless, when one cylinder is positioned at the acoustic particle velocity anti-node of certain cross-modes and another cylinder is positioned at it′s acoustic particle velocity node, i.e a cylinder that should excite the resonance and another one that should suppress it, respectively; the excitation always takes over and the resonance occurs. Moreover, as the cylinder moves closer to the duct′s wall, the Strouhal number value decrease due to the interference between the wake of the cylinder and the duct′s wall. Therefore, the acoustic resonance for this case occurs at slightly higher flow velosities.

Numerical and experimental investigation of flow-acoustic resonance of side-by-side cylinders in a duct

The phenomenon of flow-excited acoustic resonance is a design concern in many engineering applications, especially when wakes of bluff bodies are encountered in ducts, piping systems, heat exchangers, and other confined systems. In this paper, the case of self-excited acoustic resonance of two side-by-side cylinders in a duct with cross-flow is investigated both numerically and experimentally for a single spacing ratio of T/D=2.5, where D is the diameter of the cylinders and T is the centre-to-centre distance between them. The numerical investigation is performed using a finite-volume method at a Reynolds number of 3.0×104 to simulate the unsteady flow field, which is then coupled with an imposed resonant sound field of the first acoustic cross-mode of the duct calculated through the use of Finite Element Analysis (FEA). The experimental investigation has been performed using phase-locked Particle Image Velocimetry (PIV) of the flow field during the occurrence of a self-excited acoustic resonance condition in the duct. The results of both methods reveal that the flow-excited acoustic resonance produces a strong oscillatory flow pattern in the cylinder wakes, with strong in-phase vortex shedding being synchronized by the acoustic resonance. The distribution and strength of the aeroacoustic sources and sinks within the flow field have been computed by means of Howe׳s theory of aerodynamic sound for both the experimental and numerical cases, with the results of the two methods comparing favourably, showing comparable trends in the oscillating flow fields, and very similar trends in the distribution of net acoustic power.

Discussion of “Flow-Excited Acoustic Resonance Excitation Mechanism, Design Guidelines and Counter Measures,” (Ziada, S., and Lafon, P., 2014, ASME Appl. Mech. Rev., 66(1), p. 010802)

The authors have done extensive research in gathering historical background on the subject of flow excited acoustic resonance. They have provided extensive discussion to justify creative formulations for predicting the onset of resonance and estimating the associated maximum pressure amplitudes. Their approach makes use of reported experimental studies plus some of their own to make charts that should be useful for some common industrial problems. An independent scaling approach is offered in this review to verify the dominant parameters and variables employed by the authors in their predictive methods. It was found that for low Mach number flows, a specific Reynolds number (Re) dependence was missing. However, since it is known that the Strouhal dependence is very weak on Reynolds numbers up to about 105, the absence of specific Re dependence is probably inconsequential. Another concern was that interaction between the acoustics and vortex shedding or shear layer instabilities could affect the eigenfrequencies. A simple model showed that this is possible, but Quad Cities experience cited by the authors indicated one case where it was not important. The Rolls-Royce Vertical Lift System example with coaxial closed side-branches could have had a significant interaction with the annular liquid mass on eigenmodes. The mass effect resulting from the annular space connecting both branches could act less like an oscillating shear layer and more like a Helmholtz resonator. This could have a significant effect on the natural frequency of either or both branch pipes. Although that effect is not specifically considered here, if it was significant, it would be naturally embraced in a scale model based on the scaling laws presented in this review.

Flow-Excited Acoustic Resonance Excitation Mechanism, Design Guidelines, and Counter Measures

The excitation mechanism of acoustic resonances has long been recognized, but the industry continues to be plagued by its undesirable consequences, manifested in severe vibration and noise problems in a wide range of industrial applications. This paper focuses on the nature of the excitation mechanism of acoustic resonances in piping systems containing impinging shear flows, such as flow over shallow and deep cavities. Since this feedback mechanism is caused by the coupling between acoustic resonators and shear flow instabilities, attention is focused first on the nature of various types of acoustic resonance modes and then on the aeroacoustic sound sources, which result from the interaction of the inherently unstable shear flow with the sound field generated by the resonant acoustic modes. Various flow-sound interaction patterns are discussed, in which the resonant sound field can be predominantly parallel or normal to the mean flow direction and the acoustic wavelength can be an order of magnitude longer than the length scale of the separated shear flow or as short as the cavity length scale. Since the state of knowledge in this field has been recently reviewed by Tonon et al. (2011, “Aeroacoustics of Pipe Systems With Closed Branches”, Int. J. Aeroacoust., 10(2), pp. 201–276), this article focuses on the more practical aspects of the phenomenon, including various flow-sound interaction patterns and the resulting aeroacoustic sources, which are relevant to industrial applications. A general design guide proposal and practical means to alleviate the excitation mechanism are also presented. These are demonstrated by two examples of recent industrial case histories dealing with acoustic fatigue failure of the steam dryer in a boiling water reactor (BWR) due to acoustic resonance in the main steam piping and acoustic resonances in the roll posts of the Short Take-Off and Vertical Lift Joint Strike Fighter (JSF).

Closure to “Discussion of ‘Flow-Excited Acoustic Resonance: Excitation Mechanism, Design Guidelines and Counter Measures,’” (Ziada, S., and Lafon, P., 2014, Appl. Mech. Rev., 66(1), p. 010802)

Closure to “Discussion of ‘Flow-Excited Acoustic Resonance: Excitation Mechanism, Design Guidelines and Counter Measures,’” (Ziada, S., and Lafon, P., 2014, Appl. Mech. Rev., 66(1), p. 010802)

Flow-Sound Interaction Mechanism of Two Side-by-Side Cylinders in Cross-Flow

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 = 2.5, is investigated, where D is the diameter of the cylinders and T is the center-tocenter distance between them. The unsteady flow field is simulated using a finite-volume method at a Reynolds number of 30000. 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 the vortex shedding from the cylinders occurs at a single frequency with a Strouhal number of 0.217. Moreover, a symmetric wake structure downstream of the two cylinders is observed. However, when acoustic resonance is initiated the symmetric wake structure downstream of the cylinders is eliminated and the vortex shedding from both cylinders becomes antisymmetric. Moreover, two main aeroacoustic sources located just downstream of each cylinder are observed. The numerical results are compared with the experimental results presented in a previous investigation and favourable agreement is obtained.

Excitation source of a side-branch shear layer

The excitation source of flow-induced acoustic resonances in closed side-branches is characterized experimentally for circular pipes excited by turbulent flow in the main pipe. The shear layer at the branch junction is modeled by an unsteady complex source which is dependent on the Strouhal number and the acoustic particle velocity at the shear layer. The amplitude and phase of this source are determined experimentally and presented in the form of a dimensionless complex source term. This determined shear layer source term and the acoustic description of the piping system are then combined in a semi-empirical model to predict the frequency and pulsation amplitude of flow-excited acoustic resonance. The model results exemplify important experimental observations of flow excited side-branch resonances; including the occurrence of the lock-in phenomenon, the excitation of resonance by the single and double vortex modes of the shear layer, and nonlinear saturation at large pulsation amplitude due to vortex damping. The dependence of the pulsation amplitude on the Strouhal number, the static test pressure and on friction and radiation losses is also reproduced by the model. Finally, the effect of the acoustic particle velocity distribution at the branch junction on the shear layer source term is quantified.

Flow-Excited Acoustic Resonance in Industry

The excitation mechanism of acoustic resonances has long been recognized, but the industry continues to be plagued by its undesirable consequences; manifested in severe vibration and noise problems in a wide range of industrial applications. This paper focuses on the nature of the acoustic resonance excitation mechanism for the case of closed side branches because of its relative importance to industrial applications. Design charts are presented for the Strouhal number at the onset of acoustic resonance and for the acoustic source strength representing the integral effect of the shear layer at the mouth of the side branch. Because these design charts are developed from tests of cylindrical pipes conveying turbulent flow at high Reynolds numbers, they can be used in industrial applications to predict the onset flow velocity and the intensity of acoustic resonances in side branches. Two industrial examples involving flow-excited acoustic resonance of closed side branches are presented. The first example deals with acoustic fatigue failure of the steam dryer in a boiling water reactor due to acoustic resonance in the main steam piping system, whereas the second example considers acoustic resonances in the roll posts of the short take-off vertical lift (STOVL) joint strike fighter. In both examples, effective means to alleviate the acoustic resonance mechanism are discussed.