Suppression of Acoustic Resonance in Rectangular Cavities Using Spanwise Control Cylinder

2015 ◽  
Author(s):  
Ahmed Omer ◽  
Atef Mohany
Keyword(s):  
Shear Layer ◽  
Vortex Shedding ◽  
Passive Control ◽  
Acoustic Resonance ◽  
Control Technique ◽  
Resonance Excitation ◽  
Base Case ◽  
Detached Eddy Simulation ◽  
Free Shear Layer ◽  
Aspect Ratios

Flow over cavities can be a significant source of noise in many engineering applications when a coupling occurs between the flow instabilities at the cavity mouth and one of the acoustic cross-modes in the accommodating enclosure. In this paper, a passive noise control technique using a spanwise cylinder located at the cavity upstream edge is investigated experimentally for two different cavities with aspect ratios of L/D = 1.0 and 1.67, where L is the cavity length and D is the cavity depth. The effect of both the location of the cylinder and its diameter on the flow-excited acoustic resonance is investigated in air flow with Mach number up to 0.45. This passive control technique is found to be effective in suppressing the acoustic resonance excitation when compared to the base case where no cylinder is attached. It is observed that using the optimum cylinder location and diameter reduces the acoustic pressure to less than 140 Pa, compared to the base case with values exceeding 2000 Pa. Moreover, a shift in the onset of acoustic resonance to higher velocities is observed. Localized hot-wire measurements of the free shear layer at the cavity mouth during the off-resonance conditions reveal that attaching a spanwise cylinder at the cavity upstream edge reduces the spanwise correlation of the free shear layer which, in turns, reduces its susceptibility to acoustic excitation. To further understand the interaction between the cylinder’s vortex shedding and the free shear layer at the cavity mouth, a numerical simulation of the flow field using a detached eddy simulation (DES) model has been carried out. The simulation shows that the suppression occurs due to a disturbance of the cavity shear layer by the vortex shedding from the cylinder which results in altering the impingement point at the downstream edge of the cavity, and thereby weakening the feedback cycle that controls the acoustic resonance excitation.

The Effect of Upstream Edge Geometry on the Acoustic Resonance Excitation in Shallow Rectangular Cavities

2014 ◽  
Author(s):  
Ahmed Omer ◽  
Nadim Arafa ◽  
Atef Mohany ◽  
Marwan Hassan
Keyword(s):  
Flow Instability ◽  
Acoustic Resonance ◽  
Resonance Mode ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Base Case ◽  
Pressure Amplitude ◽  
Cavity Depth ◽  
Edge Geometry ◽  
Aspect Ratios

The flow-excited acoustic resonance phenomenon is created when the flow instability oscillations are coupled with one of the acoustic modes, 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 cavity with two different aspect ratios of L/D = 1 and 1.67, where L is the cavity length and D is the cavity depth, and for Mach number less than 0.5. The acoustic resonance modes of the cavity are self-excited. 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 acoustic pressure is measured with a flush-mounted microphone on the cavity floor and the velocity fluctuation of the separated shear layer before the onset of acoustic resonance is measured with a hot-wire probe. The results for each upstream cavity edge are compared with the base case when square cavity edge is used. It is observed that when chamfered edges are used, the amplitude of the first acoustic resonance mode is highly intensified with values reaching around 5000 Pa (compared to 2000 Pa for the base case) and a clear shift in its onset of resonance to higher flow velocities is observed. Similar trend is observed when round edges are used. The amplitude of the generated pressure of the first acoustic resonance mode is amplified with values exceeding 4000 Pa and a delay in its onset of acoustic resonance is observed as well. Most of the spoiler edges are found to be effective in suppressing the pressure amplitude of the excited acoustic resonance. However, the performance of each spoiler depends on its specific geometry (i.e. thickness, height, and angle) relative to the cavity aspect ratio. A summary of the results is presented in this paper.

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.

scholarly journals Instability patterns between counter-rotating disks

2003 ◽  
Vol 10 (3) ◽  
pp. 281-288 ◽  
Author(s):  
F. Moisy ◽  
T. Pasutto ◽  
M. Rabaud
Keyword(s):  
Aspect Ratio ◽  
Shear Layer ◽  
Particle Image ◽  
Shear Layer Instability ◽  
Free Shear Layer ◽  
Rotating Disks ◽  
Height Ratio ◽  
Aspect Ratios ◽  
Image Velocimetry ◽  
Local Reynolds Number

Abstract. The instability patterns in the flow between counter-rotating disks (radius to height ratio R/h from 3.8 to 20.9) are investigated experimentally by means of visualization and Particle Image Velocimetry. We restrict ourselves to the situation where the boundary layers remain stable, focusing on the shear layer instability that occurs only in the counter-rotating regime. The associated pattern is a combination of a circular chain of vortices, as observed by Lopez et al. (2002) at low aspect ratio, surrounded by a set of spiral arms, first described by Gauthier et al. (2002) in the case of high aspect ratio. Stability curve and critical modes are measured for the whole range of aspect ratios. From the measurement of a local Reynolds number based on the shear layer thickness, evidence is given that a free shear layer instability, with only weak curvature effect, is responsible for the observed patterns. Accordingly, the number of vortices is shown to scale as the shear layer radius, which results from the competition between the centrifugal effects of each disk.

Theoretical and Numerical Study of Vortex-Wake Flow Generated From Stack of Rectangular Bodies

2007 ◽  
Author(s):  
Khaled Alhussan
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Numerical Study ◽  
The Body ◽  
Fluid Particle ◽  
Wake Flow ◽  
Free Shear Layer ◽  
Complex Flow ◽  
Discrete Vortex

Flow over external bodies has been studied extensively because of their many practical applications. For example, flow past a rectangular bodies, usually experiences strong flow oscillations and boundary layer separation in the wake region behind the body. As a fluid particle flows toward the leading edge of a rectangular body, the pressure of the fluid particle increases from the free stream pressure to the stagnation pressure. The boundary layer separates from the surface forms a free shear layer and is highly unstable. This shear layer will eventually roll into a discrete vortex and detach from the surface. A periodic flow motion will develop in the wake as a result of boundary layer vortices being shed alternatively from either side of the rectangular shapes. The periodic nature of the vortex shedding phenomenon can sometimes lead to unwanted structural vibrations, especially when the shedding frequency matches one of the resonant frequencies of the structure. The work to be presented herein is a theoretical and numerical analysis of the complex fluid mechanism that occurs over stack of rectangular bodies for different number of rectangular bodies, specifically with regard to the vortex shedding and generation of wake. A number of important conclusions follow from the current research. First, study of the actual flow configuration over rectangular bodies offers some insight into the complex flow phenomena. Second, the characteristics of the vortex and wakes change considerably with the number of bodies.

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)

2013 ◽  
Vol 66 (1) ◽  
Author(s):  
Frederick J. Moody
Keyword(s):  
Shear Layer ◽  
Scaling Laws ◽  
Experimental Studies ◽  
Acoustic Resonance ◽  
Design Guidelines ◽  
Historical Background ◽  
Scale Model ◽  
Resonance Excitation ◽  
Maximum Pressure ◽  
Extensive Discussion

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.

Prediction of acoustic resonance phenomena for weapon bays using detached eddy simulation

2005 ◽  
Vol 109 (1102) ◽  
pp. 631-638 ◽  
Author(s):  
R. M. Ashworth
Keyword(s):  
Shear Layer ◽  
Hybrid Method ◽  
Acoustic Resonance ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Vortical Structures ◽  
Eddy Simulation ◽  
Resonance Phenomena ◽  
Cavity Configuration ◽  
Unsteady Rans

AbstractIt is argued that acoustic resonance phenomena in open cavities such as weapons bays cannot be adequately predicted through numerical solution of Reynolds averaged Navier-Stokes (RANS) equations. The requirement to resolve the growth of the shear layer instability from the lip of the cavity inevitably implies that turbulence further downstream is resolved while also being modelled thus making RANS over dissipative. Large eddy simulation (LES) models only unresolved scales and a hybrid method combining RANS near walls with LES in the cavity appears a practical alternative to pure RANS. This paper compares computations of the M219 cavity configuration made with unsteady RANS and with the hybrid method known as detached eddy simulation (DES). It is shown that whilst unsteady RANS and DES give very similar predictions for the 1stand 3rdmodes of the acoustic resonance the 2ndmode (which is dominant near the centre of the cavity) is absent in the RANS results but well predicted by DES. The 2ndmode is thought to arise from an interaction with vortical structures in the shear layer which are suppressed in the highly dissipative RANS method. The 4thmode, which is much weaker than the other three modes, is over-predicted by DES and under-predicted by a smaller amount in RANS.

Measurement of the Excitation Source of an Axisymmetric Shallow Cavity Shear Layer

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
S. Mohamed ◽  
H. R. Graf ◽  
S. Ziada
Keyword(s):  
Shear Layer ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Turbulent Pipe Flow ◽  
The Self ◽  
Free Shear Layer ◽  
Axisymmetric Cavity ◽  
Shallow Cavity ◽  
High Reynolds

The interaction of a cavity shear layer with the sound field of an acoustic mode can generate an aeroacoustic source which is capable of initiating and sustaining acoustic resonances in the duct housing the cavity. This aeroacoustic source is determined experimentally for an internal axisymmetric cavity exposed to high Reynolds number, fully developed turbulent pipe flow without the need to resolve the details of neither the unsteady flow field nor the flow-sound interaction process at the cavity. The experimental technique, referred to here as the standing wave method (SWM), employs six microphones distributed upstream and downstream of the cavity to evaluate the fluctuating pressure difference generated by the oscillating cavity shear layer in the presence of an externally imposed sound wave. The results of the aeroacoustic source are in good agreement with the concepts of free shear layer instability and the fluid-resonant oscillation behavior. The accuracy of the measurement technique is evaluated by means of sensitivity tests. In addition, the measured source is used to predict the self-excited acoustic resonance of a shallow cavity in a pipeline. Comparison of the predicted and measured results shows excellent prediction of the self-excited acoustic resonance, including the resonance frequency, the lock-in velocity range, and the amplitude of the self-generated acoustic resonance.

Numerical Analysis of Sweeping Jets for Active Flow Control Application

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Shawn Aram
Keyword(s):  
Flow Control ◽  
Shear Layer ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Detached Eddy Simulation ◽  
Free Shear Layer ◽  
Separation Line ◽  
Eddy Simulation ◽  
Wide Range

Abstract It has become apparent recently that the fluidic oscillators, also known as sweeping jets, can be used to create a combination of steady (streamwise vortices) and unsteady (spanwise vortices) forcing mechanisms which have the potential to fulfill many of the promises of active separation control. The fluidic oscillators contain no moving parts, but produce an unsteady component via a natural feedback loop inherent to their geometry. The oscillations are entirely self-induced and self-sustaining. Their simple and robust design and their effectiveness over a wide range of flow conditions make them more attractive than other flow control devices, such as synthetic jets and plasma actuators. Figure 1 shows the instantaneous jet generated in quiescent environment using the Improved Delayed Detached Eddy Simulation (IDDES) model, where the Large Eddy Simulation (LES) branch of the IDDES model is able to capture the turbulence structures properly. An instantaneous iso-surface of vorticity magnitude, colored by streamwise velocity for flow over a wall-mounted hump is depicted in Figure 2. As expected, a massive flow separation occurs behind the hump in the uncontrolled condition (Figure 2 (a)), with a nearly two-dimensional free shear layer at the edge of the separation line. Breakdown of the shear layer by an array of sweeping jets located slightly downstream of the separation line is seen in Figure 2 (b), which is followed by the elimination of the separation region behind hump. The three-dimensional structures generated by the sweeping jets are smaller and closer to the hump wall than those produced by the steady jets shown in Figure 2 (c). Presence of a large region of reversed flow near the hump wall in its aft section is also seen in the case of the steady jet. This study indicates a superior effectiveness of sweeping jets on separated flows.

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

2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Liuyi Jiang ◽  
Hong Zhang ◽  
Qingquan Duan ◽  
Yulong Zhang
Keyword(s):  
Natural Gas ◽  
Numerical Study ◽  
Acoustic Resonance ◽  
Side Branch ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Resonance Problem ◽  
Detached Eddy Simulation ◽  
Single Vortex ◽  
Excited Vibration

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.

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