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Direct numerical simulation of a plane turbulent wall-jet including scalar mixing
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.ORCID iD: 0000-0002-9819-2906
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.ORCID iD: 0000-0002-2711-4687
2007 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 6, 065102- p.Article in journal (Refereed) Published
Abstract [en]

Direct numerical simulation is used to study a turbulent plane wall-jet including the mixing of a passive scalar. The Reynolds and Mach numbers at the inlet are Re=2000 and M=0.5, respectively, and a constant coflow of 10% of the inlet jet velocity is used. The passive scalar is added at the inlet enabling an investigation of the wall-jet mixing. The self-similarity of the inner and outer shear layers is studied by applying inner and outer scaling. The characteristics of the wall-jet are compared to what is reported for other canonical shear flows. In the inner part, the wall-jet is found to closely resemble a zero pressure gradient boundary layer, and the outer layer is found to resemble a free plane jet. The downstream growth rate of the scalar is approximately equal to that of the streamwise velocity in terms of the growth rate of the half-widths. The scalar fluxes in the streamwise and wall-normal direction are found to be of comparable magnitude. The scalar mixing situation is further studied by evaluating the scalar dissipation rate and the mechanical to mixing time scale ratio.

Place, publisher, year, edition, pages
2007. Vol. 19, no 6, 065102- p.
Keyword [en]
Turbulent plane wall-jet, Wall-jet mixing
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-7748DOI: 10.1063/1.2732460ISI: 000247625900015Scopus ID: 2-s2.0-34447313400OAI: oai:DiVA.org:kth-7748DiVA: diva2:12868
Note
QC 20100621Available from: 2007-12-05 Created: 2007-12-05 Last updated: 2010-11-08Bibliographically approved
In thesis
1. Numerical studies of turbulent wall-jets for mixing and combustion applications
Open this publication in new window or tab >>Numerical studies of turbulent wall-jets for mixing and combustion applications
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Direct numerical simulation is used to study turbulent plane wall-jets. The investigation is aimed at studying dynamics, mixing and reactions in wall bounded flows. The produced mixing statistics can be used to evaluate and develop models for mixing and combustion. An aim has also been to develop a simulation method that can be extended to simulate realistic combustion including significant heat release. The numerical code used in the simulations employs a high order compact finite difference scheme for spatial integration, and a low-storage Runge-Kutta method for the temporal integration. In the simulations the inlet based Reynolds and Mach numbers of the wall-jet are Re = 2000 and M=0.5 respectively, and above the jet a constant coflow of 10% of the inlet jet velocity is applied. The development of an isothermal wall-jet including passive scalar mixing is studied and the characteristics of the wall-jet are compared to observations of other canonical shear flows. In the near-wall region the jet resembles a zero pressure gradient boundary layer, while in the outer layer it resembles a plane jet. The scalar fluxes in the streamwise and wall-normal direction are of comparable magnitude. In order to study effects of density differences, two non-isothermal wall-jets are simulated and compared to the isothermal jet results. In the non-isothermal cases the jet is either warm and propagating in a cold surrounding or vice versa. The turbulence structures and the range of scales are affected by the density variation. The warm jet contains the largest range of scales and the cold the smallest. The differences can be explained by the varying friction Reynolds number. Conventional wall scaling fails due to the varying density. An improved collapse in the inner layer can be achieved by applying a semi-local scaling. The turbulent Schmidt and Prandtl number vary significantly only in the near-wall layer and in a small region below the jet center. A wall-jet including a single reaction between a fuel and an oxidizer is also simulated. The reactants are injected separately at the inlet and the reaction time scale is of the same order as the convection time scale and independent of the temperature. The reaction occurs in thin reaction zones convoluted by high intensity velocity fluctuations.

Place, publisher, year, edition, pages
Stockholm: Mekanik, 2007
Series
Trita-MEK, ISSN 0348-467X ; 2007/08
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4564 (URN)
Public defence
2007-12-14, D3, Huvudbyggnaden, Lindstedtsvägen 5, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100621Available from: 2007-12-05 Created: 2007-12-05 Last updated: 2010-06-21Bibliographically approved

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Brethouwer, GeertJohansson, Arne

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