Flow-induced Acoustic Resonance Research Articles

Flow structure and aerodynamic forces of finned cylinders during flow-induced acoustic resonance

This experimental study investigated the impact of self-excitation of acoustic resonance on the fluctuating lift force, flow structure, and aeroacoustic energy transfer of spirally finned cylinders with crimps in cross-flow. Three different finned cylinders with varying fin pitch-to-root diameter ratios (p/Dr) were compared with their equivalent diameter (Deq) bare cylinders. The study found that self-excitation of acoustic resonance occurred at a lower reduced flow velocity for the finned cylinders. During acoustic resonance excitation, finned cylinders with lower p/Dr experienced an abrupt increase in the fluctuating lift force coefficient and acoustic pressure. The decomposition of the fluctuating lift force with respect to the acoustic pressure showed that the earlier onset of resonance and the abrupt increase in the lift force and acoustic pressure were due to the increased susceptibility to flow-induced acoustic resonance. Phase-locked particle image velocimetry (PIV) measurements of the vorticity field supported this finding by showing a well-organized vorticity field in the wake of these finned cylinders. However, the fins and crimps had a significant effect on the distribution of the acoustic particle velocity field compared to the bare cylinder. The presence of the fins and crimps caused the acoustic particle velocity magnitude to be concentrated within the fins and rapidly decline away from the cylinder base. As a result, the acoustic power generated was lower in the case of the finned cylinders. This ultimately resulted in a lower peak acoustic pressure and fluctuating lift force being generated in the case of the crimped spirally finned cylinders.

Effects of edge geometry on the flow-induced acoustic resonances in closed side branches

The effects of edge geometry on flow-induced acoustic resonances in closed side branches are investigated experimentally. The bilateral round edges of R = 5, 10 mm and chamfered edges of angle = 45° and C = 10 mm, where R and C are the widths of the round and chamfered edges respectively, are investigated. The round and chamfered edges both delay the onset of the acoustic resonance to a higher velocity. However, the round edges enhance the resonance normalized pressure, while the chamfered edges do not. The effects of unilateral round edges, R = 10 mm, are also investigated. The unilateral upstream round edge almost totally dominates the delay and enhancement effects, while the unilateral downstream round edge has little delay effect and suppresses the acoustic resonance partially. Finally, a method to predict the preliminary velocity range of acoustic resonance for closed side branches with round edges is proposed based on the experimental results.

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.

Numerical Study on Acoustic Resonance Excitation in Closed Side Branch Pipeline Conveying Natural Gas

Flow-induced acoustic resonance in the closed side branch of a natural gas pipeline can cause intensive vibration which threatens the safe operation of the pipeline. Accurately modeling this excitation process is necessary for a workable understanding of the genetic mechanism to resolve this problem. A realizable k-ε Delayed Detached Eddy Simulation (DDES) model was conducted in this study to numerically simulate the acoustic resonance problem. The model is shown to accurately capture the acoustic resonance phenomenon and self-excited vibration characteristics with low calculation cost. The pressure pulsation component of the acoustic resonance frequency is gradually amplified and transformed into a narrowband dominant frequency in the process of acoustic resonance excitation, forming a so-called “frequency lock-in phenomenon.” The gas is pressed into and out of the branch in sinusoidal mode during excitation. The first-order frequency, single vortex moves at the branch inlet following the same pattern. A quarter wavelength steady standing wave forms in the branch. The mechanism and characteristics presented in this paper may provide guidelines for developing new excitation suppression methods.

Flow-induced acoustic resonances in closed tandem side branches with large diameter

Flow-induced acoustic resonances in closed tandem side branches with large branch diameter are investigated experimentally. The diameters of the main pipe and branches are 305 mm and 64 mm, respectively. Three single branches with different lengths, L/d = 5.86–8.52, are investigated. The first and second hydrodynamic modes are excited at Strouhal numbers close to 0.4 and 0.8, respectively. The normalized pulsation amplitude of a certain mode decreases in branch length. For tandem branches, the resonances are rarely affected by the distance in the investigated range of Lt/D = 3.28–9.84. The branch number has no effects on dominant frequencies, but the critical velocity increases in branch number. In the delayed regions, the amplitudes in tandem branches are enhanced remarkably due to change in resonance mode. The maximum amplitudes excited by the first acoustic mode in the tandem branches, which are much higher than that in the single branch, are all in delay regions and close.

Combined Effects of Steam Wetness and Pressure on Characteristics of Acoustic Resonance Amplitude in Closed Side Branch

AbstractSteam piping and components in many industrial applications such as power plants sometimes experience structural vibration and fatigue damage caused by flow-induced acoustic resonance in piping with closed side branches. The state of steam in the steam piping can be not only dry (superheated) steam but also wet steam (i.e., a two-phase flow comprising a mixture of saturated steam and saturated water). From our prior research on the general characteristics of acoustic resonance under wet steam flows, the maximum pressure amplitudes under low-pressure wet steam were significantly lower than those under dry steam, which is considered to be caused by the presence of a liquid phase. Here, we investigate how the steam wetness and steam pressure affect the maximum pressure amplitude since practical steam piping may be exposed to various conditions. Experiments on acoustic resonance in a single side branch were conducted under high-quality wet steam flows with a steam pressure of up to 0.8 MPa and a steam quality of 0.9 < x < 1.0 as parameters. For our experimental conditions, it was confirmed that the steam pressure and steam state had little impact on the critical Strouhal number, whereas the maximum amplitudes under wet steam were markedly lower than those under dry steam. Different dependences of the maximum amplitude on the Reynolds number were confirmed for dry steam and wet steam. Moreover, the reduction of the maximum pressure amplitude under wet steam was affected by both the void fraction and the density ratio.

Frequency lock-in mechanism in flow-induced acoustic resonance of a cylinder in a flow duct

The vortex sound interaction in acoustic resonance induced by vortex shedding from a cylinder in a flow duct is numerically studied based on a nonlinear physical model, which consists of three meshless sub-models describing the vortex shedding, sound generation and propagation within the duct. In addition, the acoustic particle velocity near the separation point of the shear layer is solved and added onto the Kutta condition of the vortex shedding, which takes the acoustic feedback effect into consideration and makes the vortex sound interaction bi-directional. The predicted results of resonant frequency and amplitude are found to be in conformity with previous experiment data, especially, a continuous description of the onset–sustain–cease of lock-in phenomenon is well captured. The lock-in phenomenon is depicted as a vigorous competition between the vortex shedding frequency and the inherent frequency of the acoustic -mode . The mutual capturing behaviour of these two frequencies is dominated by . Moreover, cannot always be locked onto within the whole lock-in region, which is in marked contrast to the previous understanding. In this aspect, two lock-in regions, the synchronous region and the -mode dominant region, are defined according to the relevance of and . The maximum resonant sound appears at the end of the synchronous region. The present model not only predicts the proper characteristics of frequency lock-in as observed in experiments, but also helps to provide a more detailed understanding of the underlying lock-in mechanism.

Effects of branch length and chamfer on flow-induced acoustic resonance in closed side branches

The flow-induced acoustic resonance phenomenon may produce excessive vibrations of components in pipe systems. In this study, the effects of branch length and edge geometry on the acoustic resonance characteristics of closed side branches are investigated experimentally. Three different aspect ratios of L/d = 8, 10 and 12, where L is the branch length and d is the branch diameter, are investigated with Mach number up to 0.28. The results show that, for all the tested configurations, the second hydrodynamic mode only excites the first acoustic mode due to the small diameter of the side branches. The maximum normalized pulsation amplitude at the first acoustic mode decreases in branch length. The influence of branch length on the Strouhal numbers at onset of resonance is weak. It is about 0.55 for the first hydrodynamic mode in the case of sharp edge. The maximum normalized pulsation amplitudes are excited at a Strouhal number close to 0.4. Two different chamfers of angle 45° and C = 2.5 and 5 mm, where C is the width of the chamfered edge, are investigated. The results illustrate that the maximum normalized pulsation amplitude and the Strouhal number at onset of resonance both decrease significantly in chamfer width, which indicates chamfering is an effective method to attenuate undesirable acoustic resonance induced by closed side branches in pipe system.

Flow visualization study of flow-induced acoustic resonance in closed side branches

The phenomenon of flow-induced acoustic resonance is encountered when an acoustic mode of a side branch is coupled with the flow instability oscillations, which may generate undesirable vibrations of components in pipe systems. In particular, flow-induced acoustic resonance has caused some problems in nuclear power plants. In this study, the characteristics of the flow-induced acoustic resonance in square closed side branches are investigated experimentally. Three different aspect ratios of L/b = 5, 6 and 7, where L is the branch height and b is the branch width, are investigated with Mach number up to 0.22. The flow structures in different acoustic and hydrodynamic modes are visualized using a high speed camera, and the frequencies counted by visual measurement agree well with the frequencies measured by dynamic pressure sensors. The effects of side branch height on the amplitude and frequency characteristics of the acoustic resonance are demonstrated. The results indicate that the maximum normalized pulsation amplitudes in different resonance modes decreases in branch height, acoustic mode and hydrodynamic mode. The branch height has little influence on the Strouhal number at onset of resonance, which is about 0.55 for the first hydrodynamic mode and 0.95 for the second hydrodynamic mode in this work. The maximum normalized fluctuating pressure at the first acoustic mode occurs at a Strouhal number close to 0.43. The hysteresis phenomenon in the evolution of the fluctuating pressure as a function of the velocity is analyzed.

Experimental Investigation for Effects of Steam Wetness and Static Pressure on Acoustic Resonance Frequency at Side Branch Piping under Wet Steam Flow

Flow-induced acoustic resonances in steam piping with closed side branches cause severe structural vibration and fatigue damage of piping and components in many industrial applications such as power plants. The steam state in the steam piping of power plants is not only dry steam but also wet steam. From our previous experiments under low-pressure wet steam flow, the resonance frequencies, which is important parameter to predict acoustic resonance, under wet steam obtained by the theoretical equation and assuming a saturated sound speed were within ±6% of the measured values. However, the static pressure in practical steam piping is often higher than that in our previous experiments. In this study, we conducted experiments on acoustic resonance in a single side branch under a high-quality wet steam flow with the static pressure as parameters to investigate the effects of the static pressure on acoustic resonance frequency under wet steam flow.

Flow-Induced Acoustic Resonance in a Closed Side Branch Under a Low-Pressure Wet Steam Flow

Flow-Induced Acoustic Resonance in a Closed Side Branch Under a Low-Pressure Wet Steam Flow

多管体系での分岐部音響共鳴における湿り蒸気流中の圧力振幅特性

Flow-induced acoustic resonances in piping with closed side branches or T-junctions are one of the phenomena causing severe structural vibration and fatigue damage of piping and components in many engineering applications such as power plants. In the United States, the steam dryer of the boiling water reactor was damaged by high-cycle fatigue due to acoustic-induced vibration under a power uprating condition. Practical piping systems of power plants often have a steam flow, and moreover, the steam state can be not only dry steam but also wet steam, including nearly saturated conditions. Although many researchers have investigated acoustic resonances at side branches and T-junctions, it is considered that acoustic resonances under a wet steam flow have not yet been clarified since previous studies were mainly conducted under an air flow, and there have been few previous experiments performed under a steam flow, particularly a wet steam flow. The objective in this study is to investigate acoustic resonances in closed side branches with tandem- and coaxial-type arrangements under a wet steam flow. Experiments under a low-pressure condition for dry and wet steam flows were conducted and the results were compared. As a result, it is clarified that the effect of branch arrangements (single, tandem, coaxial) on the resonance amplitude under steam flow. In addition, differences in the amplitude response between dry and wet steam were evaluated.

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.

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.

Wake flow-induced acoustic resonance around a long flat plate in a duct

Flows around long thin blunt flat plates generate acoustic resonances when the sound frequency generated by the vortex shedding becomes close to the frequency of the acoustic mode around the plate. After their mutual capturing, the sound intensity strongly increases. To better understand this phenomenon, here we investigate the interaction between flow and flow-induced acoustic resonance around a long flat plate in a duct. Three acoustic resonance modes were observed as the flow velocity was increased. The acoustic resonance behavior is studied as a function of the shapes of the leading and trailing edges (semicircular and square) and the length of the plate (39 ≤ L/d ≤ 71). The Reynolds numbers based on the plate thickness and free-stream flow velocity ranged from 3300 to 21,300. The influence of the leading edge separation bubble and the trailing edge wake flow on the acoustic resonance is scrutinized by examining the velocity profiles, power spectra, and pressure sound level. The nonlinear behavior of the flow components in the wake is shown at monochromatic sound in the resonance regime. The difference in flow conditions around the plate for the diverse shapes of leading and trailing edges leads to the different efficiency of the sound-flow interaction, which originates the different sound level. It was found that the configuration with a semicircular leading edge and a semicircular trailing edge is the best one for generating aeroacoustic resonance. Possible physical explanations are proposed.

Development of Boiling Water Reactor Steam Dryer Loading Evaluation Methods Through Scale Model Tests Under Actual Steam Conditions

Previous plant measurements and scale model tests have demonstrated that intense fluctuating pressure acted on the steam dryer in boiling water reactors (BWRs) at higher velocity flows than in normal operation. The cause of the dryer loading was considered as flow-induced acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSLs). Acoustic resonance was considered to be generated by the interaction between the sound field and the unstable shear layer across the opening of the side branches of the SRV stub pipes. Some air scale tests have been conducted and they are useful for evaluation of occurrence of acoustic resonance in SRV stub pipes and characteristics of fluctuating pressure in MSLs. However, it is possible that differences in pressure conditions and fluid properties may cause the dryer loading to be underestimated. In the present study, we conducted scale tests under actual steam conditions to evaluate the scale model test methods for BWR dryer loading estimation. The test apparatus consisted of a steam dryer, steam dome and 4 MSLs with 20 SRV stub pipes. We demonstrated that acoustic resonance occurred in the SRV stub pipes and the fluctuating pressure which propagated from the SRVs to the dryer caused fluctuating stress on the steam dryer at the SRV resonance frequency. Acoustic resonance started when Strouhal number decreased below 0.6 in both the scale model air and steam tests. The onset of resonance due to the single vortex mode was not influenced by pressure conditions and fluid properties. The increase of fluctuating pressure due to the double vortex mode which occurred at Strouhal number values from 0.8 to 0.9 could be clearly seen in the scale model steam tests unlike in the air tests. The results showed that the self-excited acoustic resonance was affected by the static pressure and fluid properties for the scale model air tests. However, no significant influence from steam pressure was seen at pressure higher than 3 MPa. Normalized fluctuating pressure was almost the same regardless of pressure. We verified that normalization by dynamic pressure in the main pipe was a reasonable approach for evaluation of fluctuating pressure in the SRV stub pipes. Increase of fluctuating pressure due to the double vortex mode was clearly distinguished in SRV stub pipes but not strong in the MSL pipes and had insignificant impact on the dryer loading.

Study on flow-induced acoustic resonance in symmetrically located side-branches using dynamic PIV technique

Study on flow-induced acoustic resonance in symmetrically located side-branches using dynamic PIV technique

Air/steam flow and steam wetness dependence on acoustic resonance in safety relief valves

Many experimental studies related to the flow-induced acoustic resonance closed side branches have been reported. However, few studies have reported on the effects of air/steam flow and steam wetness dependence on fluctuating pressure amplitude. Therefore, we investigated the effect of air/steam flow and steam wetness dependence on fluctuating pressure amplitude by conducting a high temperature and high pressure tests at the Hitachi Utility Steam Test Leading Facility (HUSTLE). The test section consisted of a main pipe and a side branch. The side branch was mounted on the long straight main pipe. Fluctuating pressures at the end face of the side branches were measured. The following two results were obtained; the first is that the air/steam flow had little effect on the fluctuating pressure amplitude normalized by dynamic pressure and frequency normalized by the resonance frequency; the second is that under the acoustic resonance (St = 0.41) and non-resonance (St = 0.55) conditions, fluctuating pressure and frequency changed little with steam wetness. The steam wetness during the boiling water reactor operation was less than 0.1%; thus, there was no effect of steam wetness on the acoustic pressure amplitude and the frequency under this operating condition.

Aeroacoustic simulation of slender partially covered cavities using a Lattice Boltzmann method

The present investigation focuses on simulation of the aero-acoustic resonance of partially covered cavities with a width much larger than their length or depth, that represent simplified door and trunk lid gaps. These cavities are under influence of a low Mach number flow with a relatively thick boundary layer. Under certain conditions, flow-induced acoustic resonance can occur. The requirements to simulate the resonance behavior using a Lattice Boltzmann method (LBM) model are investigated. Special focus is put on the effect of simulation spanwise width and inflow conditions.In order to validate the simulations, experiments have been conducted on simplified geometries. The configuration consists of a partially covered, rectangular cavity geometry 32×50×250mm3 in size, with opening dimensions of 8×250mm. Cavity flow induced acoustic response is measured with microphones at different spanwise locations inside the cavity. Hot-wire measurements are performed to quantify the boundary layer characteristics. Furthermore, high speed time resolved particle image velocimetry is used to capture the instantaneous velocity field around the opening geometry.Flow simulations show that the turbulent fluctuation content of the boundary layer is important to correctly simulate the flow induced resonance response. A minimum simulation spanwise width is needed to show good resemblance with experimental cavity pressure spectra. When a full spanwise width simulation is employed, base mode and higher modes are retrieved.

Active Control of Flow-Induced Acoustic Resonance Through Surface Perturbation

DOI: 10.2514/1.J051748Asurface perturbation technique was applied to control the flow-induced acoustic resonance inside downstreamcavities.Thetechniquemadeuseofpiezoceramicactuatorsembeddedonthesurfaceofanupstreamtestmodelinacrossflow to generate a controllable motion to alter vortex formation, as well as the subsequent acoustic resonance.Experimentswereconductedusingvariousconfigurations.Itwasobservedthattheflow-inducedacousticresonancecould be effectively reduced after applying a surface perturbation technique. This was caused not only by animpairmentofthevortex-shedding strengthbut alsobyashiftin thesheddingfrequencyresulting fromthecontrolaction. The vortex-strength abatement mechanism was discussed, and the estimation of the frequency-shiftphenomenon as well as its effect on the impairment of acoustic resonance was experimentally assessed.