Change search
ReferencesLink to record
Permanent link

Direct link
Experimental studies of turbulent boundary layer separation and control
KTH, Superseded Departments, Mechanics.
2003 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The object ofthe present work is to experimentally study thecase ofa turbulent boundary layer subjected to an AdversePressure Gradient (APG) with separation and reattachment. Thisconstitutes a good test case for advanced turbulence modeling.The work consists ofde sign of a wind-tunnel setup, developmentofP article Image Velocimetry (PIV) measurements and evaluationtechniques for boundary layer flows, investigations ofs calingofb oundary layers with APG and separation and studies oftheturbulence structure ofthe separating boundary layer withcontrol by means ofs treamwise vortices. The accuracy ofP IV isinvestigated in the near-wall region ofa zero pressure-gradientturbulent boundary layer at high Reynolds number. It is shownthat, by careful design oft he experiment and correctly appliedvalidation criteria, PIV is a serious alternative toconventional techniques for well-resolved accurate turbulencemeasurements. The results from peak-locking simulationsconstitute useful guide-lines for the effect on the turbulencestatistics. Its symptoms are identified and criteria for whenthis needs to be considered are presented. Different velocityscalings are tested against the new data base on a separatingAPG boundary layer. It is shown that a velocity scale relatedto the local pressure gradient gives similarity not only forthe mean velocity but also to some extent for the Reynoldsshear-stress. Another velocity scale, which is claimed to berelated to the maximum Reynolds shear-stress, gives the samedegree of similarity which connects the two scalings. However,profile similarity achieved within an experiment is notuniversal and this flow is obviously governed by parameterswhich are still not accounted for. Turbulent boundary layerseparation control by means ofs treamwise vortices isinvestigated. The instantaneous interaction between thevortices and the boundary layer and the change in the boundarylayer and turbulence structure is presented. The vortices aregrowing with the boundary layer and the maximum vorticity isdecreased as the circulation is conserved. The vortices arenon-stationary and subjected to vortex stretching. Themovements contribute to large levels ofthe Reynolds stresses.Initially non-equidistant vortices become and remainequidistant and are con- fined to the boundary layer. Theamount ofi nitial streamwise circulationwas found to be acrucial parameter for successful separation control whereas thevortex generator position and size is ofseco ndary importance.At symmetry planes the turbulence is relaxed to a nearisotropic state and the turbulence kinetic energy is decreasedcompared to the case without vortices.

Keywords:Turbulence, Boundary layer, Separation,Adverse Pressure Gradient (APG), PIV, control, streamwisevortices, velocity scaling.

Place, publisher, year, edition, pages
Stockholm: Mekanik , 2003. , xii, 44 p.
Trita-MEK, ISSN 0348-467X ; 2003:08
Keyword [en]
turbulence, boundary layer, separition, adverse pressure graddient
URN: urn:nbn:se:kth:diva-3565OAI: diva2:9384
Public defence
NR 20140805Available from: 2003-06-26 Created: 2003-06-26Bibliographically approved

Open Access in DiVA

fulltext(574 kB)1638 downloads
File information
File name FULLTEXT01.pdfFile size 574 kBChecksum SHA-1
Type fulltextMimetype application/pdf

By organisation

Search outside of DiVA

GoogleGoogle Scholar
Total: 1638 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: 1017 hits
ReferencesLink to record
Permanent link

Direct link