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A Wave Expansion Method for Aeroacoustic Propagation
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.ORCID iD: 0000-0002-6813-4764
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Although it is possible to directly solve an entire flow-acoustics problem in one computation, this approach remains prohibitively large in terms of the computational resource required for most practical applications. Aeroacoustic problems are therefore usually split into two parts; one consisting of the source computation and one of the source propagation. Although both these parts entail great challenges on the computational method, in terms of accuracy and efficiency, it is still better than the direct solution alternative. The source usually consists of highly turbulent flows, which for most cases will need to be, at least partly, resolved. Then, acoustic waves generated by these sources often have to be propagated for long distances compared to the wavelength and might be subjected to scattering by solid objects or convective effects by the flow. Numerical methods used solve these problems therefore have to possess low dispersion and dissipation error qualities for the solution to be accurate and resource efficient.

The wave expansion method (WEM) is an efficient discretization technique, which is used for wave propagation problems. The method uses fundamental solutions to the wave operator in the discretization procedure and will thus produce accurate results at two to three points per wavelength. This thesis presents a method that uses the WEM in an aeroacoustic context. Addressing the propagation of acoustic waves and transfer of sources from flow to acoustic simulations. The proposed computational procedure is applied to a co-rotating vortex pair and a cylinder in cross-flow. Overall, the computed results agree well with analytical solutions.

Although the WEM is efficient in terms of the spatial discretization, the procedure requires that a Moore-Penrose pseudo-inverse is evaluated at each unique node-neighbour stencil in the grid. This evaluation significantly slows the procedure. In this thesis, a method with a regular grid is explored to speed-up this process.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , 59 p.
TRITA-AVE, ISSN 1651-7660 ; 2016:86
Keyword [en]
Sound propagation, Sound generation, Aeroacoustics, Aerodynamics, Computational fluid dynamics, Computational aeroacoustics, Numerical methods, Lighthill, Curle, Ffowcs Williams and Hawkings, Frequency-domain propagation, Wave expansion method.
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
URN: urn:nbn:se:kth:diva-196689ISBN: 978-91-7729-215-9 (print)OAI: diva2:1047622
2016-12-15, B1, Brinellvägen 23, Stockholm, 10:30 (English)

QC 20161121

Available from: 2016-11-22 Created: 2016-11-18 Last updated: 2016-12-02Bibliographically approved
List of papers
1. Simulation of aerodynamically generated noise propagation using the wave expansion method
Open this publication in new window or tab >>Simulation of aerodynamically generated noise propagation using the wave expansion method
2016 (English)In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016Conference paper (Other academic)
Abstract [en]

A numerical method to simulate aerodynamically generated sound and its propagation is presented in this paper. The flow is solved using both analytical expressions and numer- ical methods. The aeroacoustic source terms are then defined by using the aeroacoustic analogies of Lighthill, Ffowcs-Williams and Hawkings, Powell and Howe, and are evaluated from the flow solutions. The acoustic propagation with these sources is then performed using the wave expansion method. This is a discretization method suitable for solving wave propagation through inhomogeneous potential flows. Two different cases are considered in the study, a co-rotating vortex pair and the flow around a 2D cylinder at Re=150. The fo- cus of the work presented is to show a robust introduction of aeroacoustic sources in a wave expansion acoustic propagation solution procedure. The numerical results are compared to experimental and numerical results from other studies of the same configurations. 

National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-185032 (URN)
22nd AIAA/CEAS Aeroacoustics Conference, 30 May - 1 June 2016, Lyon, France

QC 20160613

Available from: 2016-04-08 Created: 2016-04-08 Last updated: 2016-11-18Bibliographically approved
2. Assembly speed-up for the wave expansion method using a uniform background mesh
Open this publication in new window or tab >>Assembly speed-up for the wave expansion method using a uniform background mesh
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-196678 (URN)

QC 20161118

Available from: 2016-11-17 Created: 2016-11-17 Last updated: 2016-12-08Bibliographically approved

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