Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Optimal initial perturbations in streamwise corner-flow
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-5913-5431
Show others and affiliations
2013 (English)Report (Other academic)
Abstract [en]

Localised optimal initial perturbations are studied to gain an understanding of the global stability properties of streamwise corner-flow. A self-similar and a modified base-flow are considered. The latter mimics a characteristic deviation from the self-similar solution, commonly observed in experiment. Poweriterations in terms of subsequent direct and adjoint linearised Navier-Stokes solution sweeps are employed to converge optimal solutions for two optimisation times. The optimal response manifests as a wave packet that initially gains energy through the Orr mechanism and continues growing exponentially thereafter. The study at hand represents the first global stability analysis of streamwise corner-flow and confirms key observations made in theoretical and/or experimental work on the subject. Namely, the presence of an inviscid instability mechanism in the near-corner region and a destabilising effect of the characteristic mean-flow deformation found in experiment.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , 13 p.
Keyword [en]
Corner flow, optimal initial condition, power iteration, adjoint
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-123194OAI: oai:DiVA.org:kth-123194DiVA: diva2:625320
Note

QC 20130604

Available from: 2013-06-04 Created: 2013-06-04 Last updated: 2015-11-25Bibliographically approved
In thesis
1. Stability and transition of three-dimensional boundary layers
Open this publication in new window or tab >>Stability and transition of three-dimensional boundary layers
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A focus has been put on the stability characteristics of different flow types existing on air vehicles. Flow passing over wings and different junctions on an aircraft face numerous local features, ranging from different pressure gradients, to interacting boundary layers. Primarily, stability characteristics of flow over a wing subject to negative pressure gradient is studied. The current numerical study conforms to an experimental study conducted by Saric and coworkers, in their Arizona State University wind tunnel experiments. Within that framework, a passive control mechanism has been tested to delay transition of flow from laminar to turbulence. The same control approach has been studied here, in addition to underling mechanisms playing major roles in flow transition, such as nonlinear effects and secondary instabilities.

Another common three-dimensional flow feature arises as a result of streamlines passing through a junction, the so called corner-flow. For instance, this flow can be formed in the junction between the wing and fuselage on a plane. A series of direct numerical simulations using linear Navier-Stokes equations have been performed to determine the optimal initial perturbation. Optimal refers to a perturbation which can gain the maximum energy from the flow over a period of time. Power iterations between direct and adjoint Navier- Stokes equations determine the optimal initial perturbation. In other words this method seeks to determine the worst case scenario in terms of perturbation growth. Determining the optimal initial condition can help improve the design of such surfaces in addition to possible control mechanisms.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. viii, 20 p.
Series
Trita-MEK, ISSN 0348-467X ; 2013:14
Keyword
Receptivity, stability, optimal growth, three-dimensional boundary layers, crossflow instability, roughness control, freestream turbulence, secondary instability
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-123175 (URN)978-91-7501-808-9 (ISBN)
Presentation
2013-06-13, E3, Osquars Backe 14, KTH, Stockholm, 10:19 (English)
Opponent
Supervisors
Projects
RECEPT
Funder
EU, FP7, Seventh Framework Programme, 76274
Note

QC 20130604

Available from: 2013-06-04 Created: 2013-06-04 Last updated: 2013-06-10Bibliographically approved
2. On stability, transition and turbulence in three-dimensional boundary-layer flows
Open this publication in new window or tab >>On stability, transition and turbulence in three-dimensional boundary-layer flows
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A lot has changed since that day on December 17, 1903 when the Wright brothers made the first powered manned flight. Even though the concepts behind flying are unaltered, appearance of stat-of-the-art modern aircrafts has undergone a massive evolution. This is mainly owed to our deeper understanding of how to harness and optimize the interaction between fluid flows and aircraft bodies. Flow passing over wings and different junctions on an aircraft faces numerous local features, for instance, acceleration or deceleration, laminar or turbulent state, and interacting boundary layers. In our study we aim to characterize some of these flow features and their physical roles.

Primarily, stability characteristics of flow over a wing subject to a negative pressure gradient are studied. This is a common condition for flows over swept wings. Part of the current numerical study conforms to existing experimental studies where a passive control mechanism has been tested to delay laminarturbulent transition. The same flow type has also been considered to study the receptivity of three-dimensional boundary layers to freestream turbulence. The work entails investigation of effects of low-level freestream turbulence on crossflow instability, as well as interaction with micron-sized surface roughness elements.

Another common three-dimensional flow feature arises as a resultof stream-lines passing through a junction, the so-calledcorner-flow. For instance, thisflow can be formed in the junction between the wing and fuselage on aplane.A series of direct numerical simulations using linear Navier-Stokes equationshave been performed to determine the optimal initial perturbation. Optimalrefers to perturbations which can gain the maximum energy from the flow overa period of time. In other words this method seeks to determine theworst-casescenario in terms of perturbation growth. Here, power-iterationtechnique hasbeen applied to the Navier-Stokes equations and their adjoint to determine theoptimal initial perturbation.

Recent advances in super-computers have enabled advance computational methods to increasingly contribute to design of aircrafts, in particular for turbulent flows with regions of separation. In this work we investigate theturbulentflow on an infinite wing at a moderate chord Reynolds number of Re= 400,000 using a well resolved direct numerical simulation. A conventional NACA4412 has been chosen for this work. The turbulent flow is characterizedusing statistical analysis and following time history data in regions with interesting flow features.

In the later part of this work, direct numerical simulation has been chosen as a tool to mainly investigate the effect of freestream turbulence on the transition mechanism of flow from laminar to turbulent around a turbine blade.

 

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2015. xvi, 49 p.
Keyword
Receptivity, stability, optimal growth, three-dimensional bound- ary layers, crossflow instability, roughness control, freestream turbulence, sec- ondary instability, transition, turbulence
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-177617 (URN)978-91-7595-783-8 (ISBN)
Public defence
2015-12-14, Sal F3, Lindstedsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20151125

Available from: 2015-11-25 Created: 2015-11-24 Last updated: 2015-11-25Bibliographically approved

Open Access in DiVA

fulltext(898 kB)276 downloads
File information
File name FULLTEXT01.pdfFile size 898 kBChecksum SHA-512
cf019a08fa9d50fdeee91a006a788d7b7ec0d5644e50a9d8b885c7d708a97dbb691b06d6c329dad6654ee3864d6aa77b37927c5b7149f349133a6965d1207504
Type fulltextMimetype application/pdf

Authority records BETA

Hanifi, ArdeshirHenningson, Dan

Search in DiVA

By author/editor
Schmidt, Oliver T.Hosseini, Seyed M.Rist, UlrichHanifi, ArdeshirHenningson, Dan
By organisation
Stability, Transition and ControlLinné Flow Center, FLOW
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
Total: 276 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

urn-nbn

Altmetric score

urn-nbn
Total: 147 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf