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Statistical Vortex-Generator-Jet Model for Turbulent Flow Separation Control
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-8692-0956
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.ORCID iD: 0000-0002-2711-4687
2013 (English)In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 51, no 5, 1119-1129 p.Article in journal (Refereed) Published
Abstract [en]

This contribution describes the development and evaluation of a new statistical modeling approach for active vortex generator jets. Previous experiments from the Technische Universitat Braunschweig and their subsequent evaluation by the present authors showed that the induced flowfield can be reasonably well represented by two-dimensional Lamb-Oseen vortices. Based on that, an analytical expression for the Lamb-Oseen-vortex-model maximum circulation Gamma(max) was derived in terms of the freestream velocity U-infinity, the jet-to-freestream velocity ratio lambda, and the jet skew angle beta, as well as the actuator diameter Phi(VGJ). Based on the parameterized results, universal values for the Lamb-Oseen-vortex-model parameters at the actuator position were determined for the development of the statistical vortex-generator-jet model. The idea behind the statistical modeling approach is that the vortices are represented by their spanwise-averaged velocity correlations, or vortex stresses, that are added to the turbulence stresses in a Reynolds stress turbulence model. The spanwise-averaged vortex stresses are derived by computing the spanwise-averaged second-order statistics of the vortex flowfleld. These vortex-generator-jet model results were compared to the spanwise-averaged vortex stresses from experiments and from fully resolved computational fluid dynamics investigations, and reasonable qualitative as well as quantitative agreement was found.

Place, publisher, year, edition, pages
2013. Vol. 51, no 5, 1119-1129 p.
Keyword [en]
Boundary-Layer, Evolution, Vortices
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-94889DOI: 10.2514/1.J051987ISI: 000318260700009ScopusID: 2-s2.0-84878335974OAI: diva2:526334

QC 20130610. Updated from submitted to published.

Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2013-06-10Bibliographically approved
In thesis
1. Computational fluid-dynamics investigations of vortex generators for flow-separation control
Open this publication in new window or tab >>Computational fluid-dynamics investigations of vortex generators for flow-separation control
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many flow cases in fluid dynamics face undesirable flow separation due to ad-verse pressure gradients on wall boundaries. This occurs, for example, due togeometrical reasons as in a highly curved turbine-inlet duct or on flow-controlsurfaces such as wing trailing-edge flaps within a certain angle-of-attack range.Here, flow-control devices are often used in order to enhance the flow and delayor even totally eliminate flow separation. Flow control can e.g. be achieved byusing passive or active vortex generators (VGs) for momentum mixing in theboundary layer of such flows. This thesis focusses on such passive and activeVGs and their modelling for computational fluid dynamics investigations.

First, a statistical VG model approach for passive vane vortex genera-tors (VVGs), developed at the Royal Institute of Technology Stockholm andthe Swedish Defence Research Agency, was evaluated and further improvedby means of experimental data and three-dimensional fully-resolved computa-tions. This statistical VVG model approach models those statistical vortexstresses that are generated at the VG by the detaching streamwise vortices.This is established by means of the Lamb-Oseen vortex model and the Prandtllifting-line theory for the determination of the vortex strength. Moreover, thisansatz adds the additional vortex stresses to the turbulence of a Reynolds-stresstransport model. Therefore, it removes the need to build fully-resolved three-dimensional geometries of VVGs in a computational fluid dynamics mesh. Usu-ally, the generation of these fully-resolved geometries is rather costly in termsof preprocessing and computations. By applying VVG models, the costs arereduced to that of computations without VVGs. The original and an improvedcalibrated passive VVG model show sensitivity for parameter variations suchas the modelled VVG geometry and the VVG model location on a flat plate inzero- and adverse-pressure-gradient flows, in a diffuser, and on an airfoil withits high-lift system extracted. It could be shown that the passive VG modelqualitatively and partly quantitatively describes correct trends and tendenciesfor these different applications.

In a second step, active vortex-generator jets (VGJs) are considered. They were experimentally investigated in a zero-pressure-gradient flat-plate flow atTechnische Universitä̈t Braunschweig, Germany, and have been re-evaluated for our purposes and a parameterization of the generated vortices was conducted. Dependencies of the generated vortices and their characteristics on the VGJsetup parameters could be identified and quantified. These dependencies wereused as a basis for the development of a new statistical VGJ model. This modeluses the ansatz of the passive VVG model in terms of the vortex model, theadditional vortex-stress tensor, and its summation to the Reynolds stress ten-sor. Yet, it does not use the Prandtl lifting-line theory for the determinationof the circulation but an ansatz for the balance of the momentum impact thatthe VGJ has on the mean flow. This model is currently under developmentand first results have been evaluated against experimental and fully-resolvedcomputational results of a flat plate without pressure gradient.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 51 p.
Trita-MEK, ISSN 0348-467X ; 2012:04
flow-separation control, vane vortex generator, vortex generator jet, zero-pressure-gradient turbulent boundary layer, adverse-pressure-gradient turbulent boundary layer, statistical modelling, turbulence, Reynolds stress- transport model, computational fluid dynamics
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-94879 (URN)978-91-7501-331-2 (ISBN)
Public defence
2012-05-16, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)

QC 20120511

Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2013-06-10Bibliographically approved

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