Similarity Variables for Sound Radiation in a Uniform Flow

Chapman, C. J.

doi:10.1006/jsvi.1999.2800

Cited by 43 publications

(35 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This model is commonly used to describe radiation of sound from the inlet of a jet engine (the duct outlet on the turbofan side), during the steady flight of a plane and is called "the inlet problem" in the literature. In this case the solution can be obtained by applying the Prandtl-Glauert (Lidoine et al, 2001) transformation and the so-called similarity variables (Chapman, 2000), which transform the convected wave equation into its ordinary form. Recently, radiation out of the duct inlet was considered in the paper by Sinayoko et al (2010) for the uniform distribution of monopole, dipole and also the so-called "equal energy per mode" sound sources, under the assumption that the sources were incoherent, so the phase relations and interference effects could be neglected and the analysis of the far field was carried out for the root mean square pressure, • the flow is assumed to be uniform in some selected parts of space, but its velocity differs.…”

Section: The Inlet and Outlet Problemmentioning

confidence: 99%

Experimental Verification of the Theoretical Model of Sound Radiation from an Unflanged Duct with Low Mean Flow

Gorazd

Jurkiewicz

Snakowska

2012

Archives of Acoustics

View full text Add to dashboard Cite

The paper deals with experimental verification of results provided by theoretical approach to the problem of sound radiation from an unflanged duct with mean flow of the medium taking into account existence of all allowable wave modes and, in particular, occurrence of the so-called unstable wave, which results in decay of radiation on and in vicinity of the duct axis. The flow is assumed to be uniform with the source of flow located inside the duct, which is the case frequently occurring in industrial systems. Mathematical considerations, accounting for multimodal and multifrequency excitation and diffraction at the duct outlet, are based on the model of the semi-infinite unflanged hard duct with flow. In the experimental set-up a fan, mounted inside the duct served as the source of flow and noise at the same time modelled as an array of uncorrelated sources of broadband noise, what led to the axisymmetrical shape of the sound pressure directivity characteristics. The theoretical analysis was carried out for the root mean square acoustic pressure in the far-field conditions. Experimental results are presented in the form of the measured pressure directivity characteristics obtained for uniform flow directed inwards and outwards the duct compared to this observed for the zero-flow case. The directivity was measured in one-third octave bands throughout five octaves (500 Hz -16 kHz) which, for a duct with radius of 0.08 m, corresponds to the range 0.74-23.65 in the reduced frequency ka (Helmholtz number) domain. The results obtained are consistent with theoretical solutions presented by Munt and Savkar, according to whom the weakening of the on-axis and close-to-axis radiation should take place in the presence of medium flow. Experimental results of the present paper indicate that this effect is observed even for the Mach number as low as 0.036.

show abstract

Section: The Inlet and Outlet Problemmentioning

confidence: 99%

Experimental Verification of the Theoretical Model of Sound Radiation from an Unflanged Duct with Low Mean Flow

Gorazd

Jurkiewicz

Snakowska

2012

Archives of Acoustics

View full text Add to dashboard Cite

show abstract

“…Note that this Green's function is only suitable for subsonic uniform mean flow because the factor  must be a real number [28].…”

Section: Acoustic Velocity Integral Formulations For Monopole and mentioning

confidence: 99%

“…On the other hand, the Lorentz or Prandtl-Glauert transformation [33,34] is an alternative method to analyze sound propagation in uniform mean flow. Investigations have indicated that a moving background flow with high Mach numbers has a significant effect on sound generation and propagation [28,[30][31][32]35], implying that the classic exponent law of radiated acoustic power [1][2][3] is only valid approximately for low-Mach-number flows and should be corrected at high Mach numbers. In a quiescent acoustic medium, acoustic power can be computed once the distribution of the acoustic pressure is known on a closed far-field surface with an enough distance between sources and observers.…”

Section: Introductionmentioning

confidence: 99%

“…As a first step, we consider the case of uniform mean flow in this paper, and earlier investigations in this area can be found in [24][25][26][27][28] [30,31] and frequencydomain [32] acoustic pressure integral formulations for the monopole and dipole sources in uniform mean flow have been deduced. The above-mentioned formulations explicitly account for the effect of the uniform mean flow on both the sound sources and sound propagation.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Vector Aeroacoustics for Uniform Mean Flow: Acoustic Velocity and Vortical Velocity

Mao

et al. 2018

AIAA Journal

View full text Add to dashboard Cite

“…En este campo, Chapman [24] derivó una familia paramétrica de variables de semejanza para la descripción de la radiación sonora en un flujo uniforme. Estas variables, basadas en las transformaciones de tipo Lorentz entre la ecuación de onda y la ecuación de onda convectiva, contienen factores Doppler y las variables generales de PrandtlGlauert, usadas en aerodinámica.…”

Section: B3 Variables De Semejanzaunclassified

Contribución al estudio y caracterización de la generación de ruido de flujo en el sistema de escape.

Verdú¹,

Concepción²

View full text Add to dashboard Cite

The studies of the vehicle noise emissions has been acquired a great relevance over the last few years for two reasons: (1) the increased social sensitivity to environmental contamination phenomena among which acoustic contamination is found, and (2) to the highest market requirements (higher "capability"vehicles at the same time as more comfortable ones: acoustic comfort).Within the complexity of the vehicle acoustic generation phenomena in this doctoral thesis, we will focus on one of the engine contributions: the exhaust noise. This component of noise is the result of two different phenomena: pulsating noise originated in the gas exchange process in the cylinders, and the flow noise induced by the turbulence phenomena developed by the mean flow that goes through the exhaust system. From these two phenomena the core of our study is flow noise and its prediction, under the motivation that as well as the pulsating noise being extensively studied and there being some prediction methods in it, the flow noise is unknown to a great extent. To this we should add, that while the pulsating noise contribution, main source, has been reduced the flow noise contribution has become more and more important in exhaust noise. The relevance of flow noise contribution is associated with its interaction with the acoustics in the system (it could amplify the main source contribution) and the existence of mufflers that work as flow noise generation sources.For the flow noise contribution study, the present doctoral thesis has been structured in six well-defined chapters.In the first chapter there is a summary of the different contributions that can be distinguished in the overall vehicle emitted noise. The importance of the flow noise study is justified from the present state of knowledge in this subject, and also the methodology bases used to perform it.In the second chapter, an experimental procedure for the estimation of the volume velocity fluctuation at the open end of the exhaust tailpipe of an internal combustion engine is presented. The different physical mechanisms involved in the emission process are analysed through the introduction of a realistic emission model. The possibility to consider that the pulsating component of the noise and the flow noise are decoupled to a certain extent is established, which means that this last component is generated by a mean "steady" flow superimposed to a pulsating flow. 8Once the possibility of studying the contribution of flow noise generated during the exhaust process as a steady flow effect has been justified. In the third chapter an experimental technique, sound intensity from in-duct measurements, is presented to analyse it. This technique allows the study of the flow noise generation by the individual component of an exhaust system (useful in the automotive industry) on a cold flow test bench. The proposed technique also allows to separate and to know the contributions in the final radiated noise of the internal and external sources of the muffler.Once the experimental pr...

show abstract

Similarity Variables for Sound Radiation in a Uniform Flow

Cited by 43 publications

References 14 publications

Experimental Verification of the Theoretical Model of Sound Radiation from an Unflanged Duct with Low Mean Flow

Experimental Verification of the Theoretical Model of Sound Radiation from an Unflanged Duct with Low Mean Flow

Vector Aeroacoustics for Uniform Mean Flow: Acoustic Velocity and Vortical Velocity

Contribución al estudio y caracterización de la generación de ruido de flujo en el sistema de escape.

Contact Info

Product

Resources

About