Turbulent Free Shear Layer Mixing and Combustion

Home
/
Papers
/
Turbulent Free Shear Layer Mixing and Combustion

Turbulent Free Shear Layer Mixing and Combustion

29 Jul 1991-pp 265-340

TL;DR: In this article, the dependence of turbulent free-shear-layer growth, mixing, and chemical reactions are discussed, with the aid of some direct consequences deducible from large-scale organization of the flow as well as from some recent models.

read less

Abstract: : Some experimental data on turbulent free-shear-layer growth, mixing, and chemical reactions are reviewed. The dependence of these phenomena on such fluid and flow parameters as Reynolds number, Schmidt number, and Mach number are discussed, with the aid of some direct consequences deducible from the large-scale organization of the flow as well as from some recent models. The mixing of two or more fluids that are entrained into a turbulent region is an important process from both a scientific and an applications vantage point. Species can be transported by turbulence to produce a more uniform distribution than some initial mean profile. This process is sometimes also referred to as mixing, without regard to whether the transported species are mixed on a molecular scale or not. If the issue of mixing arises in the context of chemical reactions and combustion, however, we recognize that only fluid mixed on a molecular scale can contribute to chemical product formation and associated heat release. The discussion in this paper will be limited to molecular mixing.

...read moreread less

Citations

PDF

Open Access

More filters

Journal Article•DOI•

The mixing transition in turbulent flows

[...]

Paul E. Dimotakis¹•Institutions (1)

California Institute of Technology¹

25 Apr 2000-Journal of Fluid Mechanics

TL;DR: In this paper, the authors proposed a Taylor Reynolds number of ReT = u[prime prime or minute] [lambda]T/v [greater, similar] 100-140 for turbulent mixing.

...read moreread less

Abstract: Data on turbulent mixing and other turbulent-flow phenomena suggest that a (mixing) transition, originally documented to occur in shear layers, also occurs in jets, as well as in other flows and may be regarded as a universal phenomenon of turbulence. The resulting fully-developed turbulent flow requires an outer-scale Reynolds number of Re = U[delta]/v [greater, similar] 1–2 × 104, or a Taylor Reynolds number of ReT = u[prime prime or minute] [lambda]T/v [greater, similar] 100–140, to be sustained. A proposal based on the relative magnitude of dimensional spatial scales is offered to explain this behaviour.

...read moreread less

546 citations

Cites background or methods or result from "Turbulent Free Shear Layer Mixing a..."

...An illustration of this transition can be found in the laser-inducedfluorescence images in figure 5, of the jet-fluid concentration in the plane of symmetry of liquid-phase turbulent jets (Dimotakis, Miake-Lye & Papantoniou 1983). Unmixed reservoir fluid (black) can be seen throughout the turbulent region and, in particular, all the way to the jet axis in the lower Reynolds number image (a) at Re ' 2.5 × 10(3). The imaged field spans 0 < z/dj < 35, where dj is the jet-nozzle diameter and, here, z is the streamwise coordinate. This is not the case in the higher Reynolds number (b) image at Re ' 10(4) (imaged field spans 0 < z/dj < 200), in which jet fluid of varying concentrations can be seen to be more volume-filling within the turbulent region. Seitzman et al. (1990) investigated the outer entrainment and mixing region, using laser-induced-fluorescence images of OH radicals in a H2–air turbulent diffusion flame....
[...]
...Specifically, the ratio N = λL λν , (25a) which measures the extent of the uncoupled range of spatial scales, i.e. the number of viscous scales within a Taylor scale, is given by N≈ 0.1Re1/4, (25b) † This calculation is discussed in Miller & Dimotakis (1991), where, for the purpose of estimating diffusion-layer thicknesses (transition from high-to-low values of the diffusing scalar; not the full high-low-high cycle), half this estimate, i.e. λν ≈ π/kν ' 25λK , was used. where the (approximate) prefactor of 0.1 was estimated for a turbulent jet....
[...]
...…of spatial scales, i.e. the number of viscous scales within a Taylor scale, is given by N≈ 0.1Re1/4, (25b) † This calculation is discussed in Miller & Dimotakis (1991), where, for the purpose of estimating diffusion-layer thicknesses (transition from high-to-low values of the diffusing…...
[...]
...I would like to acknowledge the work and discussions on this topic with P. L. Miller, and his assistance with the text, as well as the critical reading and suggestions by D. I. Pullin....
[...]
...The data, in the form of the normalized scalar fluctuation variance, are plotted in figure 6 (Miller 1991, figure 7.2)....
[...]

Journal Article•DOI•

Direct Simulation of a Self-Similar Turbulent Mixing Layer

[...]

Michael M. Rogers¹, Robert D. Moser•Institutions (1)

Ames Research Center¹

01 Feb 1994-Physics of Fluids

TL;DR: In this article, three direct numerical simulations of incompressible turbulent plane mixing layers have been performed and all the simulations were initialized with the same two velocity fields obtained from a direct numerical simulation of a turbulent boundary layer with a momentum thickness Reynolds number of 300.

...read moreread less

Abstract: Three direct numerical simulations of incompressible turbulent plane mixing layers have been performed. All the simulations were initialized with the same two velocity fields obtained from a direct numerical simulation of a turbulent boundary layer with a momentum thickness Reynolds number of 300 computed by Spalart (J. Fluid Mech. 187, 61, 1988). In addition to a baseline case with no additional disturbances, two simulations were begun with two-dimensional disturbances of varying strength in addition to the boundary layer turbulence. After a development stage, the baseline case and the case with weaker additional two-dimensional disturbances evolve self-similarly, reaching visual thickness Reynolds numbers of up to 20 000. This self-similar period is characterized by a lack of large-scale organized pairings, a lack of streamwise vortices in the 'braid' regions, and scalar mixing that is characterized by 'marching' Probability Density Functions (PDFs). The case begun with strong additional two-dimensional disturbances only becomes approximately self-similar, but exhibits sustained organized large-scale pairings, clearly defined braid regions with streamwise vortices that span them, and scalar PDFs that are 'nonmarching.' It is also characterized by much more intense vertical velocity fluctuations than the other two cases. The statistics and structures in several experiments involving turbulent mixing layers are in better agreement with those of the simulations that do not exhibit organized pairings.

...read moreread less

491 citations

Journal Article•DOI•

Compressibility Effects on Turbulence

[...]

Sanjiva K. Lele

01 Jan 1994-Annual Review of Fluid Mechanics

405 citations

The mixing transition in turbulent flows

[...]

P Aul E. D Imotakis

01 Jan 2000

308 citations

Journal Article•DOI•

Historical Survey on Enhanced Mixing in Scramjet Engines

[...]

John M. Seiner¹, S. M. Dash, D. C. Kenzakowski•Institutions (1)

University of Mississippi¹

01 Nov 2001-Journal of Propulsion and Power

TL;DR: In this paper, the authors reviewed several methods used by the scramjet community to enhance mixing of fuel with oxidizer to achieve high combustion efe ciency with reduced length combustors.

...read moreread less

Abstract: Select methods are reviewed that have been used by the scramjet community to enhance mixing of fuel with oxidizer to achieve high combustion efe ciency with reduced length combustors. The review also includes research on enhanced supersonic free shear layer mixing from the jet noise reduction community. This latter community has considered concepts involving acoustic excitation or passive excitation of shear layer instabilities to minimize noise production. Several of these concepts are amendable to active control for system optimization.

...read moreread less

274 citations