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Linear stability of plane wakes and liquid jets: global and local approach
KTH, School of Engineering Sciences (SCI), Mechanics.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , viii, 54 p.
Series
Trita-MEK, ISSN 0348-467X ; 2009:04
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-10188ISBN: 978-91-7415-259-3 (print)OAI: oai:DiVA.org:kth-10188DiVA: diva2:210107
Presentation
2009-04-16, Seminarierum S40, Teknikringen 8, KTH, 10:15 (English)
Opponent
Supervisors
Available from: 2009-04-01 Created: 2009-03-30 Last updated: 2010-11-02Bibliographically approved
List of papers
1. Global linear stability of confined wakes with co-flow
Open this publication in new window or tab >>Global linear stability of confined wakes with co-flow
(English)Manuscript (Other academic)
Abstract [en]

The global stability of confined wakes is studied numerically, using 2D global modes. The wake inlet velocity is varied, and the main focus lies in wakes with co-flow (base bleed). The density and viscosity are assumed to be constant in and outside the wake. We find that for wake Reynolds number 100, the confinement is stabilising in general. The frequency of the unstable mode increases, and wavelength decreases with confinement. By comparing with an artificial, more slowly developing wake, we conclude that the dampening effect is due to the mean flow development. For higher Reynolds numbers this effect decreases. The critical inlet velocities for which the wake becomes unstable are almost identical for unconfined and confined wakes at $Re=400$. Also, the present results are compared with results for an inviscid parallel wake found in literature, since the inlet profile is very similar to the inviscid profile. The confined wake is found to be more stable than its inviscid counterpart, while the unconfined wake is more unstable than the inviscid wake. The reason to both can be explained by the mean flow development.

 

 

 

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-10184 (URN)
Note
QC 20101102Available from: 2009-04-01 Created: 2009-03-30 Last updated: 2010-11-02Bibliographically approved
2. Stabilisation of a plane liquid sheet by gas flow: experiments and theory
Open this publication in new window or tab >>Stabilisation of a plane liquid sheet by gas flow: experiments and theory
Show others...
(English)Manuscript (Other academic)
Abstract [en]

The stability of a plane liquid jet is studied experimentally and theoretically. The main emphasis is on the effect of the surrounding air. Co-blowing with a gas velocity of the same order of magnitude as the liquid velocity is studied. Experimental results are obtained and the growth rates of the disturbances are found to be within 20\% of the values obtained from local spatial stability analysis. The effect of different parameters of the gas flow on the stability of the jet is scrutinized and it is concluded that the predicted disturbance growth is mostly sensitive to the shear from the air on the liquid surface and the velocity difference between the water and the air.

The overall disturbance growth and wavelength scales with the difference between the gas and liquid velocity.

 

 

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-10186 (URN)
Note
QC 20101102Available from: 2009-04-01 Created: 2009-03-30 Last updated: 2010-11-02Bibliographically approved
3. On the global stability of a plane liquid jet surrounded by gas: problem formulation and preliminary results
Open this publication in new window or tab >>On the global stability of a plane liquid jet surrounded by gas: problem formulation and preliminary results
(English)Manuscript (Other academic)
Abstract [en]

The global stability of a liquid sheet in gas is studied. The global 3D stability problem for a 2D base flow is formulated, including surface tension of the interface, and the viscosity and density of both phases. The implementational requirements are clarified, and met by using a parallel code for eigenvalue computations based on the mathematical software libraries PARPACK and ScaLAPACK. Preliminary eigenvalue spectra and eigenmodes are presented for the case of water jet surrounded by air.

 

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-10187 (URN)
Note
QC 20101102Available from: 2009-04-01 Created: 2009-03-30 Last updated: 2010-11-02Bibliographically approved

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