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.

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.

PIV Measurements of Aeroacoustic Sources of a Shallow Cavity in a Pipeline

2014 ◽  
Author(s):  
S. Mohamed ◽  
S. Ziada
Keyword(s):  
Finite Element ◽  
Sound Field ◽  
Sound Waves ◽  
Element Analysis ◽  
Flow Measurements ◽  
Advantages And Disadvantages ◽  
Fully Developed Turbulent Flow ◽  
Shallow Cavity ◽  
Plane Sound ◽  
High Reynolds

The aeroacoustic sources generated by flow over a cylindrical shallow cavity in a pipeline are examined in the presence of plane sound waves at various Strouhal numbers and sound intensities. The cavity is exposed to high Reynolds number fully developed turbulent flow. Extensive PIV flow measurements are performed to characterize the unsteady velocity and vorticity fields at various time instants within the sound cycle. Finite element analysis is used to obtain the particle velocity field of the sound field. The results of the PIV flow measurements and those of the finite element simulations are combined into Howe’s aeroacoustic integrand to compute the spatial and temporal distributions of the aeroacoustic sources resulting from the cavity shear layer interaction with the sound field. The results are compared with the measured aeroacoustic source strength obtained by means of the Sound Wave Method (SWM) [1]. The advantages and disadvantages of both techniques are discussed.

Investigation of Diametral Acoustic Modes in a Model of a Steam Control Gate Valve

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Oleksandr Barannyk ◽  
Peter Oshkai
Keyword(s):  
Gate Valve ◽  
Acoustic Pressure ◽  
Three Dimensional ◽  
Turbulent Pipe Flow ◽  
Mode Shapes ◽  
Main Pipeline ◽  
Scaled Model ◽  
Axisymmetric Cavity ◽  
Acoustic Modes ◽  
Shallow Cavity

The objective of the present study is to provide an insight into mechanism of coupling between turbulent pipe flow and partially trapped diametral acoustic modes associated with a shallow cavity formed by the seat of a steam control gate valve. First, the effects of the internal pipe geometry immediately upstream and downstream of the shallow cavity on the characteristics of partially trapped diametral acoustic modes were investigated. The mode shapes were calculated numerically by solving a Helmholtz equation in a three-dimensional domain corresponding to the internal geometry of the pipe and the cavity. Second, the set of experiments were performed using a scaled model of a gate valve mounted in a pipeline that contained converging–diverging sections in the vicinity of the valve. Acoustic pressure measurements at three azimuthal locations at the floor of the cavity were performed for a range of geometries of the converging–diverging section and inflow velocities. The experimentally obtained pressure data were then used to scale the amplitude of the pressure in the numerical simulations. The present results are in good agreement with the results reported in earlier studies for an axisymmetric cavity mounted in a pipe with a uniform cross-section. The resonant response of the system corresponded to the second diametral mode of the cavity. Excitation of the dominant acoustic mode was accompanied by pressure oscillations corresponding to other acoustic modes. As the angle of the converging–diverging section of the main pipeline in the vicinity of the cavity increased, the trapped behavior of the acoustic diametral modes diminished, and additional antinodes of the acoustic pressure wave were observed in the main pipeline.

A turbulent mixing layer constrained by a solid surface. Part 2. Measurements in the wall-bounded flow

1984 ◽  
Vol 139 ◽  
pp. 347-361 ◽  
Author(s):  
D. H. Wood ◽  
P. Bradshaw
Keyword(s):  
Shear Stress ◽  
Shear Layer ◽  
Normal Stress ◽  
Mixing Layer ◽  
Turbulent Energy ◽  
Free Shear Layer ◽  
Calculation Methods ◽  
Turbulent Mixing Layer ◽  
High Reynolds ◽  
The Individual

The single- and two-point measurements made in a high-Reynolds-number single-stream mixing layer growing to encounter a wind-tunnel floor on its high-velocity side that were described by Wood & Bradshaw (1982) have been extended to the wall-bounded flow. It is shown that the expected large amplification of the normal-stress components in the plane of the wall does not occur until after the mixing layer reaches the surface. There is some evidence that the double-roller component of the large-eddy structure of the original free shear layer is being re-established in the wall-bounded flow after having been stretched and weakened by the initial effect of the wall. The triple-product terms appearing in the turbulent-energy and shear-stress equations are altered in a way that cannot be reproduced by models used in current calculation methods. It appears that all the pressure-fluctuation terms in the individual normal-stress and shear-stress transport equations respond in a non-monotonic manner to the imposition of the wall. The implications for calculation methods suitable for predicting the change from an initially unaffected free shear layer to a wall-bounded flow are discussed.

Flow-Acoustic Coupling in T-Junctions: Effect of T-Junction Geometry

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
S. Ziada ◽  
K. W. McLaren ◽  
Y. Li
Keyword(s):  
Shear Layer ◽  
Flow Velocity ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Coupling Mechanism ◽  
Cross Sectional ◽  
Acoustic Coupling ◽  
Pipe Expansion ◽  
Junction Geometry ◽  
Acoustic Resonances

The flow-acoustic coupling mechanism in a T-junction, which combines flows from two branches, forming the “cross-bar” of the T-junction, into one pipe, forming the “stem” of the T-junction, is investigated experimentally. The T-junction has a step pipe expansion at its inlets. The shear layer separating from this step expansion is found to excite intense acoustic resonances over multiple ranges of flow velocity. The excited acoustic mode is confined to the branch pipes and has an acoustic pressure node at the centerline of the T-junction. The length of the expansion section of the T-junction is found to control the frequency of the shear layer oscillation and therefore determines the ranges of flow velocity over which acoustic resonances are excited. Introducing asymmetry in the T-junction expansion length has shown little influence on the excitation of acoustic resonance. An additional T-junction arrangement made of rectangular cross-sectional ducts is also investigated to facilitate a flow visualization study of unsteady flow structures in the T-junction during acoustic resonance, and thereby improve understanding of the acoustic resonance mechanism and the nature of the aero-acoustic sources in the T-junction.

scholarly journals The effect of flow oscillations on cavity drag

1987 ◽  
Vol 177 ◽  
pp. 501-530 ◽  
Author(s):  
M. Gharib ◽  
A. Roshko
Keyword(s):  
Shear Layer ◽  
Critical Value ◽  
Momentum Transport ◽  
Momentum Balance ◽  
Free Shear Layer ◽  
Periodic Oscillations ◽  
Axisymmetric Cavity ◽  
Flow Oscillations ◽  
The Mean ◽  
Cavity Width

An experimental investigation of flow over an axisymmetric cavity shows that self-sustained, periodic oscillations of the cavity shear layer are associated with low cavity drag. In this low-drag mode the flow regulates itself to fix the mean-shear-layer stagnation point at the downstream corner. Above a critical value of the cavity width-to-depth ratio there is an abrupt and large increase of drag due to the onset of the ‘wake mode’ of instability. It is also shown by measurement of the momentum balance how the drag of the cavity is related to the state of the shear layer, as defined by the mean momentum transport $\rho\overline{u}\overline{v}$ and the Reynolds stress $\rho\overline{u^{\prime}v^{\prime}}$, and how these are related to the amplifying oscillations in the shear layer. The cavity shear layer is found to be different, in several respects, from a free shear layer.

Physical Modal for Acoustic Resonance Based on the Circular Cavity Structure in the Compressor

2021 ◽  
Author(s):  
Zhao Fengtong ◽  
Chen Jianfei ◽  
Yang Mingsui ◽  
Sha Yundong ◽  
Luan Xiaochi
Keyword(s):  
Resonance Frequency ◽  
Calculation Method ◽  
Three Dimensional ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Acoustic Mode ◽  
Resonance Phenomenon ◽  
Present Calculation ◽  
Three Dimensional Model ◽  
Cavity Structure

Abstract On the basis of the rectangular cavity plate model, the Parker resonance phenomenon is investigated by using the present calculation method, which verifies the effectiveness of the numerical calculation method adopted in the paper. Acoustic resonance occurs in the multistage compressor. The acoustic resonance frequency will be locked in a specific range which presents no variation in the rotating speed. The propagation status of the sound source of the acoustic resonance frequency should be from back to forward with a helical shape. The research method of the characteristics and mechanism of the acoustic resonance is proposed based on the annular cavity structure with the numerical simulation. The calculation models of the flow field and the sound field are established. The criterion of the sound resonating with the cavity and the characteristic condition when acoustic resonance occurred in the annular cavity structure is confirmed. The theoretical model of the acoustic resonance which is developed in the paper will be useful for the the three-dimensional model investigation into the acoustic resonance in the compressor, which can provide the better exhibition of the coupling relationship between the acoustic mode in the cavity and the vibration mode of the structure when the acoustic resonance occurs.

Study on acoustic and flow-induced noise characteristics of L-shaped duct with a shallow cavity

2020 ◽  
Vol 68 (3) ◽  
pp. 209-225
Author(s):  
Masaaki Mori ◽  
Kunihiko Ishihara
Keyword(s):  
Air Conditioning ◽  
Sound Field ◽  
Frequency Range ◽  
Acoustic Characteristics ◽  
Inflow Velocity ◽  
Aerodynamic Sound ◽  
Noise Characteristics ◽  
Flow Induced Noise ◽  
Shallow Cavity ◽  
Conditioning Equipment

An aerodynamic sound generated by a flow inside a duct is one of the noise pro- blems. Flows in ducts with uneven surfaces such as grooves or cavities can be seen in various industrial devices and industrial products such as air-conditioning equipment in various plants or piping products. In this article, we have performed experiments and simulations to clarify acoustic and flow-induced sound characteris- tics of L-shaped duct with a shallow cavity installed. The experiments and simula- tions were performed under several inflow velocity conditions. The results show that the characteristics of the flow-induced sound in the duct are strongly affected by the acoustic characteristics of the duct interior sound field and the location of the shallow cavity. Especially, it was found that the acoustic characteristics were af- fected by the location of the shallow cavity in the frequency range between 1000 Hz and 1700 Hz.

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