A note on the radiative directivity patterns of duct acoustic modes

Homicz, Gregory F.; Lordi, J. A.

doi:10.1016/s0022-460x(75)80175-1

Cited by 127 publications

(71 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Strong pressure exerted on manufacturers to produce quieter systems resulted in extensive theoretical, numerical and experimental research work on the problem leading to elaboration of more exact and thorough description of the acoustic field phenomena reflecting the real conditions in which these appliances operate with better accuracy. This was achieved by the use of more complicated mathematical models, accounting for diffraction at the duct outlet and presence of higher wave modes (Levine, Schwinger, 1948;Weinstein, 1969;Snakowska, Wyrzykowski, 1986;Homicz, Lordi, 1975;Joseph, Morfey, 1999), flow of the medium inside the duct (Savkar, 1975;Munt, 1977;1990) or in the whole space (Sinayoko et al, 2010). In each case was accomplished by solving appropriate wave equation (either with or without flow) with adequate boundary conditions.…”

Section: Introductionmentioning

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: Introductionmentioning

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

“…The target solutions of this buffer zone are set to zero to absorb spurious numerical reflections. The far-field directivity from Munt's analytical solution [15] was used in validation, but its amplitude was scaled to that used by Homicz and Lordi [27] so that the results could also be compared in the situation of a uniform background flow. Hence, in terms of comparison with the Munt's solutions [15], only the radiation peak angle, the shadow interference dip angle, and the dynamic range of the pressure were compared.…”

Section: A Setupmentioning

confidence: 99%

Efficient Computation of Spinning Modal Radiation Through an Engine Bypass Duct

Huang

Chen

et al. 2008

AIAA Journal

View full text Add to dashboard Cite

The aim of this work is to accurately and efficiently predict sound radiation out of a duct with flow. The sound propagation inside a generic engine bypass duct, refractions by the shear layer of the exhaust flow, and propagation in the near field are the main focus of the study. The prediction uses either a modified form of linearized Euler equations or an alternative model based on acoustic perturbation equations, which were extended to cylindrical coordinates. The two models were compared on a canonical case of sound propagation out of a semi-infinite duct with flow. Good agreements between the predictions were achieved. The more general case of a generic aircraft engine bypass duct with flow was then investigated with the technique of adaptive mesh refinement to increase the computational efficiency. The results show that both linearized Euler equations and acoustic perturbation equations models can predict the near-field sound propagation and far-field directivity. The acoustic perturbation equations model, however, is more adaptive for its suitability to an arbitrary background mean flow.

show abstract

“…Firstly, a benchmark case, the spinning mode acoustic radiation from an unflanged duct described by Homicz & Lordi [149], is solved to verify the performance of the AMR code. A schematic of the problem is shown in Figure 4.10.…”

Section: Spinning Mode Duct Radiationmentioning

confidence: 99%

Adaptive Mesh Refinement for Computational Aeroacoustics

Huang

Zhang

2005

11th AIAA/CEAS Aeroacoustics Conference

View full text Add to dashboard Cite

This thesis describes a parallel block-structured adaptive mesh refinement (AMR) method that is employed to solve some computational aeroacoustic problems with the aim of improving the computational efficiency. AMR adaptively refines and coarsens a computational mesh along with sound propagation to increase grid resolution only in the area of interest.While sharing many of the same features, there is a marked difference between the current and the established AMR approaches. Rather than low-order schemes generally used in the previous approaches, a high-order spatial difference scheme is employed to improve numerical dispersion and dissipation qualities. To use a highorder scheme with AMR, a number of numerical issues associated with fine-coarse block interfaces on an adaptively refined mesh, such as interpolations, filter and artificial selective damping techniques and accuracy are addressed. In addition, the asymptotic stability and the transient behaviour of a high-order spatial scheme on an adaptively refined mesh are also studied with eigenvalue analysis and pseudospectra analysis respectively. In addition, the fundamental AMR algorithm is simplified in order to make the work of implementation more manageable.Particular emphasis has been placed on solving sound radiation from generic aero-engine bypass geometry with mean flow. The approach of AMR is extended to support a body-fitted multi-block mesh. The radiation from an intake duct is modelled by the linearised Euler equations, while the radiation from an exhaust duct is modelled by the extended acoustic perturbation equations to suppress hydrodynamic instabilities generated in a sheared mean flow. After solving the near-field sound solution, the associated far-field sound directivity is estimated by solving the Ffowcs Williams-Hawkings equation. The overall results demonstrate the accuracy and the efficiency of the presented AMR method, but also reveal some limitations. The possible methods to avoid these limitations are given at the end of this thesis.

show abstract

A note on the radiative directivity patterns of duct acoustic modes

Cited by 127 publications

References 6 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

Efficient Computation of Spinning Modal Radiation Through an Engine Bypass Duct

Adaptive Mesh Refinement for Computational Aeroacoustics

Contact Info

Product

Resources

About