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Interaction of acoustic waves and micron-sized surface roughness elements in a swept-wing boundary layer
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
2016 (English)Report (Other academic)
Abstract [en]

E↵ect of acoustic waves on the control performance of distributed micron-sized roughness elements in a swept-wing boundary layer is investigated through direct numerical simulations. The flow configuration conforms to experiments by Kachanov et al. (2015) who observed either no significant influence of acoustic waves on the transition location or small stabilisation e↵ect. In this work, a base set up for natural transition scenario is first established by introducing unsteady background noise in the boundary layer. The natural transition is then delayed using control roughness elements. Introduction of acoustic waves to the controlled flow promotes the transition location. In all these flow cases, stationary primary crossflow vortices dominate the disturbance environment and unsteady disturbances experience an explosive growth prior to transition. The spatial distribution of the energy production associated with z-type modes shows an increase in the local transfer of energy from the modified mean flow to perturbations. Simulation of flow with control roughness elements and acoustic waves as the only source of unsteady disturbances shows no influence of acoustic wave in transition to turbulence. 

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-196875OAI: oai:DiVA.org:kth-196875DiVA: diva2:1049476
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

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