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
Numerical Studies of Turbulent and Separeted Flows
KTH, School of Engineering Sciences (SCI), Mechanics.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , x, 36 p.
Series
Trita-MEK, ISSN 0348-467X ; 2006:12
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-4044OAI: oai:DiVA.org:kth-4044DiVA: diva2:10535
Public defence
2006-06-16, Sal F3, Lindstedtsvägen 26, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100830Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-08-30Bibliographically approved
List of papers
1. The influence of periodic excitation on a turbulent separation bubble
Open this publication in new window or tab >>The influence of periodic excitation on a turbulent separation bubble
2006 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 76, no 1, 1-21 p.Article in journal (Refereed) Published
Abstract [en]

Turbulent separation limits the performance in many engineering applications, for example creating pressure losses in diffuser like flows or stall on aircraft wings. In the present study the turbulent boundary layer flow over a flat plate separating due to an adverse pressure gradient is studied as a model problem and the effect of periodic excitation in both time and space is investigated through direct numerical simulations. Linear stability analysis is used to analyse the sensitivity of the flow with respect to time-periodic excitations. The dependence on position, amplitude and frequency of the forcing is investigated. For a certain frequency range at sufficiently high amplitudes, it is possible to eliminate the separated region. Furthermore, three-dimensional effects are studied by applying a steady spanwise forcing as well as a both time-dependent and spanwise varying forcing. A forcing varying in spanwise direction is shown to be the most effective in eliminating the separated region, whereas two-dimensional time-periodic excitation was not as efficient as it was expected.

Keyword
turbulent boundary layer, separation, periodic excitation, direct numerical-simulation, boundary-layer separation, backward-facing step, flow separation, reattachment, vicinity, mild
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-15487 (URN)10.1007/s10494-005-9004-4 (DOI)000235748700001 ()2-s2.0-33644674514 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Instability characteristics of harmonic disturbances in a turbulent separation bubble
Open this publication in new window or tab >>Instability characteristics of harmonic disturbances in a turbulent separation bubble
Show others...
2005 (English)In: Proceedings of XVII Congresso Aimeta di Meccanica Teorica e Applicata, 2005Conference paper, Published paper (Refereed)
Abstract [en]

The instability characteristics of a turbulent flat plate boundary layer separating under a strong adverse pressure gradient are examined. The analysis is based on the data of direct numerical simulation. A theoretical model of harmonic perturbations is considered, including the contribution of the turbulent part of the flow, to investigate the stability characteristics of the flow. The structure of the organized waves is also investigated by means of Proper Orthogonal Decompositions (POD).

Keyword
separated flow, direct numerical simulation, flow instability, POD
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-24241 (URN)
Conference
Proceedings of XVII Congresso Aimeta di Meccanica Teorica e Applicata, 2005
Note

QC 20100830

Available from: 2010-08-30 Created: 2010-08-30 Last updated: 2016-08-18Bibliographically approved
3. The effect of the sweep angle on the turbulent separation bubble on a flate plate
Open this publication in new window or tab >>The effect of the sweep angle on the turbulent separation bubble on a flate plate
2006 (English)Report (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-24242 (URN)
Note
QC 20100830Available from: 2010-08-30 Created: 2010-08-30 Last updated: 2010-08-30Bibliographically approved
4. Simulations of turbulent flow in a plane asymmetric diffuser
Open this publication in new window or tab >>Simulations of turbulent flow in a plane asymmetric diffuser
2007 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 79, no 3, 275-306 p.Article in journal (Refereed) Published
Abstract [en]

Large-eddy simulations (LES) of a planar, asymmetric diffuser flow have been performed. The diverging angle of the inclined wall of the diffuser is chosen as 8.5 degrees, a case for which recent experimental data are available. Reasonable agreement between the LES and the experiments is obtained. The numerical method is further validated for diffuser flow with the diffuser wall inclined at a diverging angle of 10 degrees, which has served as a test case for a number of experimental as well as numerical studies in the literature (LES, RANS). For the present results, the subgrid-scale stresses have been closed using the dynamic Smagorinsky model. A resolution study has been performed, highlighting the disparity of the relevant temporal and spatial scales and thus the sensitivity of the simulation results to the specific numerical grids used. The effect of different Reynolds numbers of the inflowing, fully turbulent channel flow has been studied, in particular, Re-b = 4,500, Re-b = 9,000 and Re-b = 20,000 with Re-b being the Reynolds number based on the bulk velocity and channel half width. The results consistently show that by increasing the Reynolds number a clear trend towards a larger separated region is evident; at least for the studied, comparably low Reynolds-number regime. It is further shown that the small separated region occurring at the diffuser throat shows the opposite behaviour as the main separation region, i.e. the flow is separating less with higher Re-b . Moreover, the influence of the Reynolds number on the internal layer occurring at the non-inclined wall described in a recent study has also been assessed. It can be concluded that this region close to the upper, straight wall, is more distinct for larger Re-b . Additionally, the influence of temporal correlations arising from the commonly used periodic turbulent channel flow as inflow condition (similar to a precursor simulation) for the diffuser is assessed.

Keyword
turbulent separation, diffuser flow, large-Eddy simulation, dynamic Smagorinsky model, large-eddy simulation, direct numerical-simulation, boundary-layer, separated flow, channel, models
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-16949 (URN)10.1007/s10494-007-9091-5 (DOI)000249405300005 ()2-s2.0-34548592017 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
5. Early turbulent evolution of the Blasius wall jet
Open this publication in new window or tab >>Early turbulent evolution of the Blasius wall jet
2006 (English)In: Journal of turbulence, ISSN 1468-5248, Vol. 7, 1-17 p.Article in journal (Refereed) Published
Abstract [en]

The first direct numerical simulation that is sufficiently large to study the self-similar behaviour of a turbulent wall jet is performed. The investigation is an extension of the simulation performed by Levin et al. (2005, A study of the Blasius wall jet. Journal of Fluid Mechanics, 539, 313-347). The same numerical method is used, but a significantly larger computational domain enables us to follow the development of the flow throughout the transition into its early turbulent evolution. Two-dimensional waves and streamwise elongated streaks, matched to measured disturbances, are introduced in the flow to trigger a natural transition mechanism. The Reynolds number is 3090 based on the inlet velocity and the nozzle height. The simulation provides detailed visualisations of the flow structures and statistics of mean flow and turbulent stresses. A weak subharmonic behaviour in the transition region is revealed by animations of the flow. The averaged data are presented in both inner and outer scalings in order to identify self-similar behaviour. Despite the low Reynolds number and the short computational domain, the turbulent flow exhibits a reasonable self-similar behaviour, which is most pronounced with inner scaling in the near-wall region

Keyword
Direct numerical simulation, Streaks, Transition; Turbulence, Wall jet
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-8904 (URN)10.1080/14685240600854884 (DOI)000242548700001 ()2-s2.0-33845970201 (Scopus ID)
Note
QC 20100830Available from: 2005-12-08 Created: 2005-12-08 Last updated: 2010-12-06Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Herbst, Astrid
By organisation
Mechanics
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 311 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