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A Reynolds stress closure description of separation control with vortex generators in a plane asymmetric diffuser
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-2711-4687
2007 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 11, 115108- p.Article in journal (Refereed) Published
Abstract [en]

A way to model the effects of streamwise vortices in a turbulent flow with one homogeneous direction is presented. The Reynolds averaged Navier-Stokes equations are solved with a differential Reynolds stress turbulence model. Assuming that the vortices can be approximated with the Lamb-Oseen model, wall-normal Reynolds stress distributions are calculated, corresponding to the spanwise variances of the estimated velocity distribution downstream of the vortex generators. The Reynolds stress contributions that are due to the vortex generators are added to the Reynolds stresses from the turbulence model so as to mimic the increased mixing due to the vortex generators. Volume forces are applied also in the mean momentum equations to account for the drag of the vortex generators. The model is tested and compared with experimental data from a plane asymmetric diffuser flow which is separating without vortex generators. The results indicate that the model is able to mimic the major features of vortex generator flow control and that the flow case in question is susceptible to separation control. The model results show that the pressure recovery of the diffuser could be increased by almost 10% by applying vortex generators and that, if keeping the shape of the vortex generators fixed, their optimal position is close to the diffuser inlet. Computations also indicated that the time to re-establish the separation zone when the control suddenly is turned off is substantially longer than the time it takes to remove the separation after the control is turned on again. Some work on adapting a differential Reynolds stress turbulence model was necessary in order to make it capable of realistic predictions of the asymmetric diffuser flow in which the vortex generator model is tested. However, the main focus of the article is on the modelling of vortex generator effects.

Place, publisher, year, edition, pages
2007. Vol. 19, no 11, 115108- p.
Keyword [en]
near-wall turbulence, flows, model, simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-6047DOI: 10.1063/1.2800877ISI: 000251325700040Scopus ID: 2-s2.0-36849006329OAI: oai:DiVA.org:kth-6047DiVA: diva2:10632
Note
Uppdaterad från manuskript till artikel: 20100923. QC 20100923Available from: 2006-08-09 Created: 2006-08-09 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Experimental and computational studies of turbulent separating internal flows
Open this publication in new window or tab >>Experimental and computational studies of turbulent separating internal flows
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The separating turbulent flow in a plane asymmetric diffuser with 8.5 degrees opening angle is investigated experimentally and computationally. The considered flow case is suitable for fundamental studies of separation, separation control and turbulence modelling. The flow case has been studied in a specially designed wind-tunnel under well controlled conditions. The average velocity and fluctuation fields have been mapped out with stereoscopic particle image velocimetry (PIV). Knowledge of all velocity components allows the study of several quantities of interest in turbulence modelling such as the turbulence kinetic energy, the turbulence anisotropy tensor and the turbulence production rate tensor. Pressures are measured through the diffuser. The measured data will form a reference database which can be used for evaluation of turbulence models and other computational investigations. Time-resolved stereoscopic PIV is used in an investigation of turbulence structures in the flow and their temporal evolution. A comparative study is made where the measured turbulence data are used to evaluate an explicit algebraic Reynolds stress turbulence model (EARSM). A discussion regarding the underlying reasons for the discrepancies found between the experimental and the model results is made. A model for investigations of separation suppression by means of vortex generating devices is presented together with results from the model in the plane asymmetric diffuser geometry. A short article on the importance of negative production-rates of turbulent kinetic energy for the reverse flow region in separated flows is presented. A detailed description of the experimental setup and PIV measurement procedures is given in a technical report.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. ix, 185 p.
Series
Trita-MEK, ISSN 0348-467X ; 2006:15
Keyword
Fluid mechanics, turbulence, flow separation, turbulence modelling, asymmetric diffuser, boundary layer, PIV, vortex generator, separation control
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4071 (URN)91-7178-416-0 (ISBN)
Public defence
2006-09-08, Salongen, Biblioteket KTH, Osquars backe 31, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100923Available from: 2006-08-09 Created: 2006-08-09 Last updated: 2010-09-23Bibliographically approved

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Johansson, Arne V.

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