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A new way to describe the transition characteristics of a rotating-disk boundary-layer flow
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-1146-3241
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
2012 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, no 3, 031701- p.Article in journal (Refereed) Published
Abstract [en]

A new method of graphically representing the transition stages of a rotating-disk flow is presented. The probability density function contour map of the fluctuating azimuthal disturbance velocity is used to show the characteristics of the boundary-layer flow over the rotating disk as a function of Reynolds numbers. Compared with the variation of the disturbance amplitude (rms) or spectral distribution, this map more clearly shows the changing flow characteristics through the laminar, transitional, and turbulent regions. This method may also be useful to characterize the different stages in the transition process not only for the rotating-disk flow but also for other flows.

Place, publisher, year, edition, pages
2012. Vol. 24, no 3, 031701- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-93941DOI: 10.1063/1.3696020ISI: 000302224600001Scopus ID: 2-s2.0-84859347277OAI: oai:DiVA.org:kth-93941DiVA: diva2:524741
Funder
Swedish Research CouncilStandUp
Note

QC 20120503

Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Experimental study of the rotating-disk boundary-layer flow
Open this publication in new window or tab >>Experimental study of the rotating-disk boundary-layer flow
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Rotating-disk flow has been investigated not only as a simple model of cross flow instability to compare with swept-wing flow but also for industrial flow applications with rotating configurations. However the exact nature of laminar-turbulent transi- tion on the rotating-disk flow is still major problem and further research is required for it to be fully understood, in particular, the laminar-turbulent transition process with absolute instability. In addition the studies of the rotating-disk turbulent boundary- layer flow are inadequate to understand the physics of three-dimensional turbulent boundary-layer flow.

In present thesis, a rotating-rotating disk boundary-layer flow has been inves- tigated experimentally using hot-wire anemometry. A glass disk with a flat surface has been prepared to archieve low disturbance rotating-disk environment. Azimuthal velocity measurements using a hot-wire probe have been taken for various conditions. To get a better insight into the laminar-turbulent transition region, a new way to describe the process is proposed using the probability density function (PDF) map of azimuthal fluctuation velocity.

The effect of the edge of the disk on the laminar-turbulent transition process has been investigated. The disturbance growth of azimuthal fluctuation velocity as a function of Reynolds number has a similar trend irrespective of the various edge conditions.

The behaviour of secondary instability and turbulent breakdown has been in- vestigated. It has been found that the kinked azimuthal velocity associated with secondary instability just before turbulent breakdown became less apparent at a cer- tain wall normal heights. Furthermore the turbulent breakdown of the stationary mode seems not to be triggered by its amplitude, however, depend on the appearance of the travelling secondary instability.

Finally, the turbulent boundary layer on a rotating disk has been investigated. An azimuthal friction velocity has been directly measured from the azimuthal velocity profile in the viscous sub-layer. The turbulent statistics normalized by the inner and outer sclaes are presented. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 50 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:12
Keyword
Fluid mechanics, boundary layer, rotating disk, laminar-turbulent transition, convective instability, absolute instability, secondary instability, crossflow instability, hot-wire anemometry.
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-95147 (URN)978-91-7501-409-8 (ISBN)
Presentation
2012-06-08, Seminar room, Brinellvägen 32, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2010-3886
Note
QC 20120529Available from: 2012-05-29 Created: 2012-05-14 Last updated: 2012-05-29Bibliographically approved
2. Studies of the rotating-disk boundary-layer flow
Open this publication in new window or tab >>Studies of the rotating-disk boundary-layer flow
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rotating-disk boundary layer is not only a simpler model for the study of cross-flow instability than swept-wing boundary layers but also a useful simplification of many industrial-flow applications where rotating configurations are present. For the rotating disk, it has been suggested that a local absolute instability, leading to a global instability, is responsible for the small variation in the observed laminar-turbulent transition Reynolds number however the exact nature of the transition is still not fully understood. This thesis aims to clarify certain aspects of the transition process. Furthermore, the thesis considers the turbulent rotating-disk boundary layer, as an example of a class of three-dimensional turbulent boundary-layer flows.

The rotating-disk boundary layer has been investigated in an experimental apparatus designed for low vibration levels and with a polished glass disk that gave a smooth surface. The apparatus provided a low-disturbance environment and velocity measurements of the azimuthal component were made with a single hot-wire probe. A new way to present data in the form of a probability density function (PDF) map of the azimuthal fluctuation velocity, which gives clear insights into the laminar-turbulent transition region, has been proposed. Measurements performed with various disk-edge conditions and edge Reynolds numbers showed that neither of these conditions a↵ect the transition process significantly, and the Reynolds number for the onset of transition was observed to be highly reproducible.

Laminar-turbulent transition for a ‘clean’ disk was compared with that for a disk with roughness elements located upstream of the critical Reynolds number for absolute instability. This showed that, even with minute surface roughness elements, strong convectively unstable stationary disturbances were excited. In this case, breakdown of the flow occurred before reaching the absolutely unstable region, i.e. through a convectively unstable route. For the rough disk, the breakdown location was shown to depend on the amplitude of individual stationary vortices. In contrast, for the smooth (clean-disk) condition, the amplitude of the stationary vortices did not fix the breakdown location, which instead was fixed by a well-defined Reynolds number. Furthermore, for the clean-disk case, travelling disturbances have been observed at the onset of nonlinearity, and the associated disturbance profile is in good agreement with the eigenfunction of the critical absolute instability.

Finally, the turbulent boundary layer on the rotating disk has been investigated. The azimuthal friction velocity was directly measured from the azimuthal velocity profile in the viscous sublayer and the velocity statistics, normalized by the inner scale, are presented. The characteristics of this three-dimensional turbulent boundary-layer flow have been compared with those for the two-dimensional flow over a flat plate and close to the wall they are found to be quite similar but with rather large differences in the outer region. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. viii, 58 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:27
Keyword
Fluid mechanics, laminar-turbulent transition, convective instability, absolute instability, secondary instability, hot-wire anemometry
National Category
Other Physics Topics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-158973 (URN)978-91-7595-416-5 (ISBN)
Public defence
2015-01-30, F3, Lindstedsv. 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 76324
Note

QC 20150119

Available from: 2015-01-19 Created: 2015-01-16 Last updated: 2015-01-19Bibliographically approved

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