Aeroacoustic Source Distribution Around Four Cylinders Orientated in a Square

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

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

Analysis of the Noise Level Generated by Axial Flow Fan Composed of Radial-Bladed Centrifugal Rotor

2014 ◽  
Author(s):  
S. S. Borges ◽  
R. Barbieri ◽  
P. S. B. Zdanski
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Axial Flow ◽  
Acoustic Resonance ◽  
Pressure Level ◽  
Resonance Mode ◽  
Numerical Techniques ◽  
Cooling Systems ◽  
Centrifugal Fans ◽  
Motor Cooling

The objective of this work is to present, by means of experimental, analytical and numerical techniques that sound pressure level generated by radial-bladed centrifugal fans of electric motor cooling systems may be expressed by a logarithmical ratio of the peripheral velocity of rotor, volumetric flow and efficiency of the fan. The proposed methodology proved to be efficient and simple in the prediction of generated noise by radial-bladed centrifugal fans of TEFC motors with accuracy of ± 3 dB. In addition, the acoustic resonance mode of the fan cavity were determined by means of numerical simulations, which its results were validated through experiments using waterfall spectrum.

Experimental and Numerical Investigation of Blades Effect on Aerodynamic Performance of Small Axial Flow Fan

2011 ◽  
Author(s):  
Li Zhang ◽  
Yingzi Jin ◽  
Yi Zhao ◽  
Pin Liu
Keyword(s):  
Flow Field ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Pressure Level ◽  
Aerodynamic Noise ◽  
Blade Number ◽  
Small Axial Flow Fan ◽  
Fan Blade

To explore the effect of blade numbers on aerodynamic performance and noise of small axial flow fan, the steady flow field and the unsteady flow field of fan models with 6 different blade numbers (such as 5, 7, 9, 11, 13, 15) are numerically calculated. Then the internal flow distribution, static characteristic and aerodynamic noise are analyzed among six different fan models. The analysis results show: (1)Total pressure and efficiency generally maintain the trend of first increasing and then decreasing with increasing blade numbers, and it is the maximum when fan blade number is 11. The flow rate coupled with the maximum efficiency has never changed with increasing the blade numbers. (2)With increasing blade numbers, overall sound pressure level of the aerodynamic noise is gradually decreasing near the outlet of fan tip, while it is first decreasing and then increasing before decreasing again at 1 meter away from the central axis of the impeller along the outlet. When fan blade number is 11, overall sound pressure level of the aerodynamic noise is the greatest. Furthermore, the aerodynamic performance tests of fan models with 6 different blade numbers are carried out, the results of between the tests and the numerical calculations are roughly consistent. The research results will provide the proof of the parameter optimization and the structure design for high performance and low noise small axial fans.

Investigation of turbulence-induced quadrupole source acoustic characteristics of a three-dimensional hydrofoil

2020 ◽  
Vol 34 (14) ◽  
pp. 2050145
Author(s):  
Rennian Li ◽  
Wenna Liang ◽  
Wei Han ◽  
Hui Quan ◽  
Rong Guo ◽  
...  
Keyword(s):  
Vortex Shedding ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Three Dimensional ◽  
Sound Field ◽  
Leading Edge ◽  
Pressure Level ◽  
Acoustic Characteristics ◽  
Eddy Simulation ◽  
Unsteady Fluid

In order to investigate the turbulence-induced acoustic characteristics of hydrofoils, the flow and sound field for a model NH-15-18-1 asymmetric hydrofoil were calculated based on the mixed method of large eddy simulation (LES) with Lighthill analogy theory. Unsteady fluid turbulent stress source around the hydrofoil were selected as the inducements of quadrupole sound. The average velocity along the mainstream direction was calculated for different Reynolds numbers [Formula: see text]. Compared to experimental measurements, good agreement was seen over a range of [Formula: see text]. The results showed that the larger the [Formula: see text], the larger the vortex intensity, the shorter the vortex initial shedding position to the leading edge of the hydrofoil, and the higher the vortex shedding frequency [Formula: see text]. The maximum sound pressure level (SPL) of the hydrofoil was located at the trailing edge and wake of the hydrofoil, which coincided with the velocity curl [Formula: see text] distribution of the flow field. The maximum SPL of the sound field was consistent with the location of the vortex shedding. There were quadratic positive correlations between the total sound pressure level (TSPL) and the maximum value of the vortex intensity [Formula: see text] and velocity curl, which verified that shedding and diffusion of vortices are the fundamental cause of the generation of the quadrupole source noise.

The Effect of Sound Pressure on the Aeroacoustic Sources Around Two Ducted Tandem Cylinders

2010 ◽  
Author(s):  
Shane Leslie Finnegan ◽  
Craig Meskell ◽  
Samir Ziada
Keyword(s):  
Flow Velocity ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Pressure Level ◽  
Acoustic Energy ◽  
Source Distribution ◽  
Main Stream ◽  
Tandem Cylinders ◽  
Mainstream Flow

An empirical investigation of the spatial distribution of aeroacoustic sources around two tandem cylinders subject to ducted flow and forced transverse acoustic resonance is described. The work builds on a previous investigation by the authors and utilises Howe’s theory of aerodynamic sound. The influence of the sound pressure level in the duct on the strength and location of the aeroacoustic sources in the flow was the main focus of the investigation and experiments to resolve the aeroacoustic source distribution were concentrated at a low main-stream flow velocity (before acoustic-Strouhal coincidence), at a medium mainstream flow velocity (just after acoustic-Strouhal coincidence) and at a high mainstream flow velocity (substantially higher than acoustic-Strouhal coincidence). The sound pressure level was found to have a considerable effect on the “lock-in”’ range of the cylinders which widened as the sound pressure level increased. A proposed normalisation of the net acoustic energy transfer per spanwise location appears to show good metric for the distribution of the aeroacoustic sources in the flow field. Using this, it was found that the amplitude of the sound pressure had a negligible influence on the aeroacoustic sources in the wake and the gap region for all the tested cases apart from the lowest flow velocity. This particular case showed indications that the aeroacoustic source strength and location could be altered for certain changes in sound pressure level.

Computational investigation of noise interaction for a nano counter-rotating rotor in a static condition

2018 ◽  
Vol 07 (01n02) ◽  
pp. 1850004
Author(s):  
Zhen Liu ◽  
Chen Bu ◽  
Xiangxu Kong ◽  
Dong Yang ◽  
Bingfei Li
Keyword(s):  
Flow Field ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Static Condition ◽  
Pressure Level ◽  
Tip Vortex ◽  
Field Analysis ◽  
Aeroacoustic Noise ◽  
Eddy Simulation ◽  
Coaxial Rotor

The interaction between the upper and lower rotors greatly influences the aeroacoustic characteristics of a counter-rotating nano-coaxial rotor. To study this influence, a numerical investigation was carried out. The unsteady flow field of a single upper rotor was first studied with a large-eddy simulation computational fluid dynamics method coupled with a sliding-mesh technique. The Ffowcs Williams–Hawking equation method was used to investigate the aeroacoustic characteristics of the upper rotor based on the flow field. An experimental setup was established to validate the computational approach. The experimental results matched well with the computational results. Additionally, results show that the peak value of the total sound pressure level appeared near the blade tip, which verified that the tip vortex was one of the most important sources of rotor noise. Then the aeroacoustic noise of the nano-coaxial rotor was studied numerically. It was found that the total sound pressure level of the nano-coaxial rotor was greater than that of the upper rotor. Flow field analysis showed that the shedding vortices of the upper rotor interacted with the lower rotor, resulting in a blade–vortex interaction. It was evident that the aeroacoustic noise was enhanced by the interference between the upper and lower rotors.

Effect of Blade Numbers on Aerodynamic Performance and Noise of Small Axial Flow Fan

2011 ◽  
Vol 199-200 ◽  
pp. 796-800
Author(s):  
Li Zhang ◽  
Ying Zi Jin
Keyword(s):  
Flow Field ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Pressure Level ◽  
Aerodynamic Noise ◽  
Blade Number ◽  
Small Axial Flow Fan ◽  
Fan Blade

To more fully explore the effect of blade numbers on aerodynamic performance and noise of small axial flow fan, some solutions are adopted to obtain the parameters’ distribution of the flow field.Firstly, the standard k-ε turbulence model is used to calculate the steady flow field of six different fan blades(such as 5,7,9,11,13,15) , and the SIMPLE algorithm is applied to couple vecolity and pressure. Secondly, the large eddy simulation in conjunction with the FH-W noise model are used to compute the unsteady flow field and noise. Finally, the experimental results verify that the calculation methods of steady flow field and unsteady flow field are correct. The conclusions show: (1)Total pressure and efficiency generally maintain the trend of firstly increasing and then decreasing with increasing the blade numbers, and it is the greatest when fan blade number is 11. The flow rate coupled with the maximum efficiency has never changed with increasing the blade numbers. (2)With the increasing blades, overall sound pressure level of the aerodynamic noise is gradually decreasing near the outlet of fan tip, while it is firstly decreasing and then increasing before decreasing again 1 meter away from the central axis of the impeller along the outlet. When fan blade number is 11, overall sound pressure level of the aerodynamic noise is the greatest.

Interaction Between Acoustic Resonance and Fluidelastic Instability in a Normal Triangular Tube Array

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Flow Velocity ◽  
Acoustic Field ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Acoustic Resonance ◽  
Pressure Level ◽  
Structural Damping ◽  
Duct Acoustics ◽  
Fluidelastic Instability ◽  
Independent Parameters

The interaction between acoustic resonance and damping controlled fluidelastic instability (FEI) in a normal triangular tube array (P∕d=1.32) has been investigated. The duct acoustics were excited with speakers placed adjacent to the tube array to artificially replicate flow-induced acoustic resonance. The paper deals with the effect on the rms level of tube vibration of three independent parameters: imposed acoustic sound pressure level, freestream flow velocity, and structural damping. A fall in the FEI vibration amplitude with increasing sound pressure level in the tube array has been observed. In addition, the imposed acoustic field delays the onset of damping controlled fluidelastic instability. The effects of flow velocity and structural damping in conjunction with acoustic resonance on the rms of tube displacement are discussed. While the current study has clearly captured the phenomenon of interaction between the fluidelastic motion at approximately 10Hz and the acoustic field at approximately 1kHz, it is not apparent what the physical mechanism at work might be.

Effect of Fins on Vortex Shedding Noise Generated From a Circular Cylinder in Cross Flow

2010 ◽  
Author(s):  
Hiromitsu Hamakawa ◽  
Yuji Kouno ◽  
Eiichi Nishida
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Finned Tube ◽  
Pressure Level ◽  
Spanwise Direction ◽  
Equivalent Diameter ◽  
Karman Vortex ◽  
Bare Tube

In the present paper, the effect of twist-serrated fins around a bare tube on the Aeolian tone was experimentally investigated. These fins were mounted spirally around a bare tube and had the same geometry as those actually used in boiler tubes. We measured the intensity of velocity fluctuation, spectrum of velocity fluctuation, coherence of Karman vortex in the spanwise direction, dynamic lift force, and sound pressure level of the aerodynamic noise generated from finned tubes with various fin pitches. An Aeolian tone induced by Karman vortex shedding was observed in the case of a finned tube, although the complicated fin was mounted around a bare tube. A decrease in the pitch of the fin effectively caused an increase in the equivalent diameter, which acted as the characteristic length of a cylinder with fins. The equivalent diameter depended on the Reynolds number. We modified a relation to calculate the characteristic diameter of the finned tube, which in turn was used to calculate the Strouhal number. The coherent scales in the spanwise direction for the cases with various fin pitches were slightly larger than that of a simple circular cylinder. It is known that the sound pressure level of the Aeolian tone depends on the coherent scale of the Karman vortex in the spanwise direction. However, when the pitch of the fins decreased, the peak level of the sound pressure spectrum decreased. A correlation analysis between the flow field and Aeolian tone was carried out.

scholarly journals Study on the influence of blade outlet cutting on hydraulic noise of centrifugal pump with low specific speed

2020 ◽  
Vol 12 (9) ◽  
pp. 168781402096063
Author(s):  
Xiaorui Cheng ◽  
Tianpeng Li ◽  
Peng Wang
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sound Field ◽  
Pressure Level ◽  
Field Calculation ◽  
Impeller Blade ◽  
Low Specific Speed ◽  
Specific Speed

In order to study the influence of blade outlet cutting width on hydrodynamic excitation noise of the centrifugal pump with low specific speed, five schemes are used to perform V-shaped cutting on the outlet of the impeller blade are studied in this study. Based on Lighthill acoustic analogy, combining computational fluid dynamics and computational acoustics, RNG k-ε turbulence model is used to calculate internal unsteady flow field of the centrifugal pump, and the acoustic solution is based on the flow field calculation. The results show that the pressure pulsation can reflect the sound pressure level to a certain extent; proper cutting of the blade outlet can improve the flow state of the rear cavity of the centrifugal pump and make the flow uniform; the V-shaped cutting of the blade outlet also can reduce the dynamic and static interference between the impeller outlet and the volute tongue, effectively reducing the sound pressure level of the internal sound field, when the blade outlet cutting width is a/ b2 = 33.33%, the inlet sound pressure level and the outlet sound pressure level are decreased by 4.8% and 7.2%, respectively. In terms of internal sound field, the sound pressure level at the outlet of the pump is obviously higher than that at the inlet.

Experimental Investigation of the Acoustic Power Around Two Tandem Cylinders

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

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

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