Calculation of Sound Propagation in Nonuniform Flows:  Suppression of Instability Waves

Agarwal, Anurag; Morris, Philip J.; Mani, Ramani

doi:10.2514/1.619

Cited by 100 publications

(36 citation statements)

References 9 publications

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“…The Discontinuous Galerkin Method has been applied for solving the Linearised Euler Equations [9]. However, issues related to impedance boundary conditions [10] and linear instabilities [11] are still under investigation.…”

Section: Introductionmentioning

confidence: 99%

A High-Order Finite Element Method for the Linearised Euler Equations

Hamiche¹,

Gabard²,

Bériot³

2016

Acta Acustica united with Acustica

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SummarySound propagation in complex non-uniform mean flows is an important feature of turbofan exhaust noise radiation. The Linearised Euler Equations are able to represent the strong shear layer refraction effects on the sound field, as well as multiple length scales. Frequency domain solvers are suitable for tonal noise and considered a way to avoid linear instabilities, which may occur with time domain solvers. However, the classical Finite Element Method suffers from dispersion error and high memory requirements. These shortcomings are particularly critical for high frequencies and for the Linearised Euler Equations, which involve up to five unknowns. In this paper, a high-order Finite Element Method is used to solve the Linearised Euler Equations in the frequency domain in order to overcome those issues. The model involves high-order polynomial shape functions, unstructured triangular meshes, numerical stabilisation and Perfectly Matched Layers. The acoustic radiation from a straight circular semi-infinite hard-wall duct with several mean flow configurations is computed. Comparisons with analytic solutions demonstrate the method accuracy. The acoustic and vorticity waves are well represented, as well as the refraction of the sound field across the jet shear layer. The high-order approach allows to use coarse meshes, while maintaining a sufficient accuracy. The benefits in terms of memory requirements are significant when compared to standard low-order Finite Element Method.

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Section: Introductionmentioning

confidence: 99%

A High-Order Finite Element Method for the Linearised Euler Equations

Hamiche¹,

Gabard²,

Bériot³

2016

Acta Acustica united with Acustica

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“…A similar modification for LEE can be found in the literature [16]. To soothe the concerns [13] raised over the nonphysical modification, an alternative model based on acoustic perturbation equations (APE) [17,18] was employed in this work. The original APE model was modified for axisymmetric applications.…”

Section: = @Wmentioning

confidence: 99%

“…The unstable components develop exponentially to finally corrupt the desired acoustic solutions. It was a common practice to avoid the numerical instabilities by solving the problem in the frequency domain [3,13,14]. To use the current time-domain code, the LEE model was "degraded" by removing several terms that are singular in a sheared background flow [7].…”

Section: = @Wmentioning

confidence: 99%

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Efficient Computation of Spinning Modal Radiation Through an Engine Bypass Duct

Huang

Chen

et al. 2008

AIAA Journal

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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.

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“…This formulation is not without problems as hydrodynamic instabilities, which would be limited physically by nonlinear effects, can be triggered and can overwhelm the acoustic solution. Agarwal et al [39] have developed a frequency domain solution method that overcomes this problem.…”

Section: Radiation and Propagationmentioning

confidence: 99%

An Aeroacoustic Analysis of Wind Turbines

Morris

Long²,

Brentner

2004

42nd AIAA Aerospace Sciences Meeting and Exhibit

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This paper describes computational aeroacoustic methods that are being applied to predict the noise radiated by wind turbines. Since the wind turbine noise problem is very challenging, only some of the important noise sources and mechanisms are being considered. These are airfoil self-noise, the effects of blade rotation, and the propagation of sound over large distances. Two aspects of airfoil self-noise are being studied. The first is the relatively low frequency noise generated by deep stall and the second is trailing edge noise. The noise associated with blade rotation includes the effects of blade rotation on the blade aerodynamics, incoming gusts, incoming atmospheric turbulence and wind shear. The unsteady flow simulations are coupled to the radiated noise field with the permeable surface Ffowcs Williams -Hawkings formulation. For longrange noise propagation predictions, methods based on solutions of the linearized Euler equations or the Parabolic Equation approximation are discussed. Alternative methods for the implementation of boundary conditions for the propagation studies are also included.

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Calculation of Sound Propagation in Nonuniform Flows: Suppression of Instability Waves

Cited by 100 publications

References 9 publications

A High-Order Finite Element Method for the Linearised Euler Equations

A High-Order Finite Element Method for the Linearised Euler Equations

Efficient Computation of Spinning Modal Radiation Through an Engine Bypass Duct

An Aeroacoustic Analysis of Wind Turbines

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