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Stability analysis of experimental flow fields behind aporous cylinder for the investigation of the large-scale wake vortices
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-3251-8328
(English)Report (Other academic)
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-47334OAI: diva2:454786
QC 20111108Available from: 2011-11-08 Created: 2011-11-08 Last updated: 2011-11-08Bibliographically approved
In thesis
1. Experimental design and vortex analyses in turbulent wake flows
Open this publication in new window or tab >>Experimental design and vortex analyses in turbulent wake flows
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A new experimental setup for studies on wake flow instability and its control that successfully has been designed and manufactured, is introduced and de- scribed. The main body is a dual-sided flat plate with an elliptic leading edge and a blunt trailing edge. Permeable surfaces enable boundary layer suction and/or blowing that introduce the unique feature of adjusting the inlet condition of the wake created behind the plate. This, in combination with a trailing edge that is easily modified, makes it an ideal experiment for studies of different control methods for the wake flow instability as well as extensive parameter studies. Experimental validation of the setup has been performed by means of measurements of the wake symmetry and boundary layer velocity profiles at the trailing edge. Some preliminary results on the Strouhal number versus different inlet conditions are reported.

Additionally, an in-house vortex detection (VD) program has been developed in order to detect, analyse and compare small-scale vortical structures in instantaneous velocity fields from flow measurements. This will be a powerful tool for comparison of wake characteristics for varying inlet conditions and control methods in the new experimental setup. Measurements from three completely separate experimental setups with different geometries and flow cases, have been analysed by the VD-program.


       i.     In order to obtain improved ventilation we have studied the effect of pulsating inflow into a closed volume compared to having the inflow at a constant flow rate. We show that the number of small-scale eddies is significantly increased and that the stagnation zones are reduced in size, which enhances the mixing.


      ii.     Instantaneous velocity fields in the wake behind a porous cylinder subjected to suction or blowing through the entire cylinder surface have also been analysed using the VD-program. The results show that the major change for different levels of blowing or suction is the location of vortices while the most common vortex size and strength are essentially unchanged.


     iii.     Another study on how the geometry of a V-shaped mixer in a pipe flow affects the mixing have also been examined, where no general differences were found between different thicknesses, why a thickness that is favourable from an acoustic point of view can be chosen.


We also propose a new method, using global mode analysis on experimental data, showing that randomly ordered snapshots of the velocity field behind the porous cylinder can be re-ordered and phase-averaged.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. viii, 29 p.
Trita-MEK, ISSN 0348-467X ; 2011:12
bluff bodies, wake flow, experimental design, vortex detection, flow control, asymptotic suction boundary layer
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-46203 (URN)978-91-7501-157-8 (ISBN)
Public defence
2011-11-11, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:30 (English)
Active control of vortex shedding behind bluff bodies
QC 20111108Available from: 2011-11-08 Created: 2011-11-02 Last updated: 2011-11-08Bibliographically approved

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Fallenius, Bengt E. G.Fransson, Jens H. M.
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