Change search
ReferencesLink to record
Permanent link

Direct link
Application of biorthogonal eigenfunction system for extraction of Tollmien-Schlichting waves in acoustic receptivity simulations
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0002-5913-5431
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. henning@mech.kth.se.ORCID iD: 0000-0001-7864-3071
2016 (English)Report (Other academic)
Abstract [en]

Acoustic receptivity of a two-dimensional boundary layer on a flat plate with elliptic leading edge is studied through direct numerical simulation (DNS). Sound waves are modelled by a uniform oscillation of freestream boundaries in time which results to an infinite-wavelength acoustic wave. Acoustic disturbances interact with strong streamwise gradients at the leading edge or surface non- homogeneities and create Tollmien-Schlichting (TS) waves inside the boundary layer. Measuring amplitude of TS waves created by sound waves is challenging due to presence of Stokes wave (acoustic boundary layer) with the same temporal frequency of TS waves. In this study biorthogonal eigenfunction system of local linear stability equations has been utilised to extract TS wave amplitudes. This method is based on the concept of using adjoint mode as a projector where the TS amplitude is obtained by projecting the DNS solution onto adjoint TS modes. However, the computed TS wave amplitude employing this method found to be modulated. It is shown that the modulation is due to existence of a small amplitude wave in the DNS data that is not expandable onto the basis of local linear stability equations. 

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016.
National Category
Mechanical Engineering Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-196874OAI: oai:DiVA.org:kth-196874DiVA: diva2:1049473
Note

QC 20161125

Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2016-11-25Bibliographically approved
In thesis
1. On stability and receptivity of boundary-layer flows
Open this publication in new window or tab >>On stability and receptivity of boundary-layer flows
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work is concerned with stability and receptivity analysis as well as studies on control of the laminar-turbulent transition in boundary-layer flows through direct numerical simulations. Various flow configurations are considered to address flow around straight and swept wings. The aim of this study is to contribute to a better understanding of stability characteristics and different means of transition control of such flows which are of great interest in aeronautical applications.

Acoustic receptivity of flow over a finite-thickness flat plate with elliptic leading edge is considered. The objective is to compute receptivity coefficient defined as the relative amplitude of acoustic disturbances and TS wave. The existing results in the literature for this flow case plot a scattered image and are inconclusive. We have approached this problem in both compressible and incompressible frameworks and used high-order numerical methods. Our results have shown that the generally-accepted level of acoustic receptivity coefficient for this flow case is one order of magnitude too high.

The continuous increase of computational power has enabled us to perform global stability analysis of three-dimensional boundary layers. A swept flat plate of FSC type boundary layer with surface roughness is considered. The aim is to determine the critical roughness height for which the flow becomes turbulent. Global stability characteristics of this flow have been addressed and sensitivity of such analysis to domain size and numerical parameters have been discussed.

The last flow configuration studied here is infinite swept-wing flow. Two numerical set ups are considered which conform to wind-tunnel experiments where passive control of crossflow instabilities is investigated. Robustness of distributed roughness elements in the presence of acoustic waves have been studied. Moreover, ring-type plasma actuators are employed as virtual roughness elements to delay laminar-turbulent transition.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 49 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2016:17
Keyword
boundary layer receptivity, acoustic receptivity, swept-wing flow, crossflow vortices, roughness element, global stability analysis, direct numerical simulation, plasma actuator
National Category
Mechanical Engineering Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-196878 (URN)978-91-7729-184-8 (ISBN)
Public defence
2016-12-09, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20161124

Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2016-11-25Bibliographically approved

Open Access in DiVA

fulltext(14284 kB)17 downloads
File information
File name FULLTEXT01.pdfFile size 14284 kBChecksum SHA-512
5c2b23e9378b620757a1b749c56389e6a34c455d3ee18daaf1da03019f6ccaf18341dfcd2ca763f5caa1cd3513cc8fe11800a8bdbfbe9742b6523cb859db1053
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Shahriari, NimaHanifi, ArdeshirHenningson, Dan S.
By organisation
Stability, Transition and ControlLinné Flow Center, FLOWSeRC - Swedish e-Science Research Centre
Mechanical EngineeringFluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
Total: 17 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 71 hits
ReferencesLink to record
Permanent link

Direct link