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Simulation of Sound Absorption by Scattering Bodies Treated with Acoustic Liners Using a Time-Domain Boundary Element Method
| Content Provider | Semantic Scholar |
|---|---|
| Author | Pizzo, Michelle E. Hu, Fang Q. Nark, Douglas M. |
| Copyright Year | 2018 |
| Abstract | Reducing aircraft noise is a major objective in the field of computational aeroacoustics. When designing next generation quiet aircraft, it is important to be able to accurately and efficiently predict the acoustic scattering by an aircraft body from a given noise source. Acoustic liners are an effective tool for achieving aircraft noise reduction and are characterized by a frequency-dependent impedance (or admittance, defined as the inverse of impedance) value. Converted into the timedomain using Fourier transforms, an impedance boundary condition can be used to simulate the acoustic wave scattering by geometric bodies treated with acoustic liners. Two different acoustic liner models will be discussed in which the liner impedance is specified at a given frequency. Both impedance and admittance boundary conditions will be derived for each model and coupled with a time-domain boundary integral equation to model acoustic scattering by a flat plate consisting of both un-lined and lined surfaces. The scattering solution will be obtained iteratively using both spatial and temporal basis functions and the stability will be demonstrated through eigenvalue analysis. Introduction Reducing aircraft noise is a major objective in the field of computational aeroacoustics. When designing next generation quiet aircraft, it is important to be able to accurately and efficiently predict the acoustic scattering by an aircraft body from a given noise source [1] [2] [3] [4]. Acoustic scattering problems can be modeled using boundary element methods (BEMs) by reformulating the linear convective wave equation as a boundary integral equation (BIE), both in the frequency-domain and the time-domain; BEMs reduce the spatial dimension by one allowing for the integration over a surface instead of a volume [5] [6] [7] [8] [9] [10]. Frequency-domain solvers are the most commonly used and researched within literature; they have a reduced computational cost [11] and allow for modeling time-harmonic fields at a single frequency [10] [11] [12]. Moreover, frequencydomain solvers eliminate the growth of KelvinHelmholtz instabilities caused by the velocity shear of two interacting fluids, and allow for an impedance boundary condition to be imposed more naturally [12]. Despite the benefits of frequency-domain solvers, there are several distinct advantages to using time-domain solvers [1] [13]. For example, time-domain solvers allow for the simulation and study of broadband sources and time-dependent transient signals whereas studying broadband sources in the frequency-domain carry a high computational cost. Time-domain solvers also allow for the scattering solution at all frequencies to be obtained within a single computation and avoid needing to invert a large dense linear system as is required in the frequency-domain. Moreover, a time-domain solution is more naturally coupled with a nonlinear computational fluids dynamics simulation of noise sources. Time-domain BIEs (TD-BIEs) unfortunately have an intrinsic numerical instability due to resonant frequencies, which result from non-trivial solutions in the interior domain. TD-BIE solvers also carry a high computational cost. In recent years, numerical techniques for modeling acoustic wave scattering using TD-BIEs have been under development [1] [2] [3] [4]. It has been shown that stability can be realized through implementing a Burton-Miller type reformulation of the TD-BIE and computational cost can be reduced using fastalgorithms and high performance computing. In the present study, a time-domain BEM (TDBEM) is used to solve a Burton-Miller type TD-BIE reformulated from the convective wave equation. The scattering solution is obtained using temporal and spatial basis functions and a March-On-in-Time scheme in which a sparse matrix is solved iteratively. Scattering problems are considered for geometric bodies consisting of both rigid and soft surfaces – surfaces in which an acoustic liner is applied. Typically composed of an array of Helmholtz resonators, acoustic liners are used for dissipating the incident acoustic wave and are |
| File Format | PDF HTM / HTML |
| DOI | 10.2514/6.2018-3456 |
| Alternate Webpage(s) | http://vsgc.odu.edu/wp-content/uploads/2019/05/Michelle-Rodio.pdf |
| Alternate Webpage(s) | https://doi.org/10.2514/6.2018-3456 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
