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Direct numerical simulation of non-isothermal turbulent wall-jets
KTH, School of Engineering Sciences (SCI), Mechanics.
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
2009 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 21, no 3Article in journal (Refereed) Published
Abstract [en]

Direct numerical simulations of plane turbulent nonisothermal wall jets are performed and compared to the isothermal case. This study concerns a cold jet in a warm coflow with an ambient to jet density ratio of ρa/ρj = 0.4, and a warm jet in a cold coflow with a density ratio of ρa/ρj = 1.7. The coflow and wall temperature are equal and a temperature dependent viscosity according to Sutherland’s law is used. The inlet Reynolds and Mach numbers are equal in all these cases. The influence of the varying temperature on the development and jet growth is studied as well as turbulence and scalar statistics. The varying density affects the turbulence structures of the jets. Smaller turbulence scales are present in the warm jet than in the isothermal and cold jet and consequently the scale separation between the inner and outer shear layer is larger. In addition, a cold jet in a warm coflow at a higher inlet Reynolds number was also simulated. Although the domain length is somewhat limited, the growth rate and the turbulence statistics indicate approximate self-similarity in the fully turbulent region. The use of van Driest scaling leads to a collapse of all mean velocity profiles in the near-wall region. Taking into account the varying density by using semilocal scaling of turbulent stresses and fluctuations does not completely eliminate differences, indicating the influence of mean density variations on normalized turbulence statistics. Temperature and passive scalar dissipation rates and time scales have been computed since these are important for combustion models. Except for very near the wall, the dissipation time scales are rather similar in all cases and fairly constant in the outer region.

Place, publisher, year, edition, pages
2009. Vol. 21, no 3
Keyword [en]
flow simulation, jets, shear turbulence
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-7749DOI: 10.1063/1.3081554ISI: 000264782100032ScopusID: 2-s2.0-64249085661OAI: diva2:12869
QC 20100617Available from: 2007-12-05 Created: 2007-12-05 Last updated: 2012-01-18Bibliographically 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
Trita-MEK, ISSN 0348-467X ; 2007/08
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-4564 (URN)
Public defence
2007-12-14, D3, Huvudbyggnaden, Lindstedtsvägen 5, Stockholm, 10:15
QC 20100621Available from: 2007-12-05 Created: 2007-12-05 Last updated: 2010-06-21Bibliographically approved

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