Heat release effects on shear-layer growth and entrainment

Hermanson, James C.; Mungal, M. G.; Dimotakis, Paul E.

doi:10.2514/3.9666

Cited by 31 publications

(5 citation statements)

References 21 publications

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“…There are deep incursions of freestream fluid into the mixing layer, suggesting that the intermittency at the edges of the mixing layer is lower in the RRM-type inflow case, when compared to the WN-type simulation. Qualitatively at least the structures present in the RRM-type inflow simulation bear remarkable similarity to those observed in a low heat release experimental visualisation [24].…”

Section: Flow Structuresupporting

confidence: 70%

Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

Huang

McMullan

2021

Theor. Comput. Fluid Dyn.

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In this paper, the mixing and combustion at low-heat release in a turbulent mixing layer are studied numerically using large eddy simulation. The primary aim of this paper is to successfully replicate the flow physics observed in experiments of low-heat release reacting mixing layers, where a duty cycle of hot structures and cool braid regions was observed. The nature of the imposed inflow condition shows a dramatic influence on the mechanisms governing entrainment, and mixing, in the shear layer. An inflow condition perturbed by Gaussian white noise produces a shear layer which entrains fluid through a nibbling mechanism, which has a marching scalar probability density function where the most probable scalar value varies across the layer, and where the mean-temperature rise is substantially over-predicted. A more sophisticated inflow condition produced by a recycling and rescaling method results in a shear layer which entrains fluid through an engulfment mechanism, which has a non-marching scalar probability density function where a preferred scalar concentration is present across the thickness of the layer, and where the mean-temperature rise is predicted to a good degree of accuracy. The latter simulation type replicates all of the flow physics observed in the experiment. Extensive testing of subgrid-scale models, and simple combustion models, shows that the WALE model coupled with the Steady Laminar Flamelet model produces reliable predictions of mixing layer diffusion flames undergoing with fast chemistry.

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Section: Flow Structuresupporting

confidence: 70%

Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

Huang

McMullan

2021

Theor. Comput. Fluid Dyn.

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“…Even the centreline-based metric in figure 11 captured this trend, because of the influence of the shear layer vortices on the potential core. The reduction in entrainment of higher-density fluid into a lower-density vortical structure has been seen in a number of prior reactive shear layer studies, both experimental (Hermanson, Mungal & Dimotakis 1987;Hasselbrink & Mungal 2001) and computational (Karagozian & Marble 1986). Figure 21 further demonstrates that, for a relatively weak convectively unstable shear layer, as for the equidensity JICF with J = 41 in figure 21(a), accelerating vorticity rollup by creating an absolutely unstable shear layer (figure 21b) did appear to improve mixing.…”

Section: Comparison Of Centreplane-and Cross-section-based Unmixednessmentioning

confidence: 50%

Transverse jet mixing characteristics

et al. 2016

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This experimental study explores and quantifies mixing characteristics associated with a gaseous round jet injected perpendicularly into cross-flow for a range of flow and injection conditions. The study utilizes acetone planar laser-induced fluorescence imaging to determine mixing metrics in both centreplane and cross-sectional planes of the jet, for a range of jet-to-cross-flow momentum flux ratios (2 J 41), density ratios (0.35 S 1.0) and injector configurations (flush nozzle, flush pipe and elevated nozzle), all at a fixed jet Reynolds number of 1900. For the majority of conditions explored, there is a direct correspondence between the nature of the jet's upstream shear layer instabilities and structure, as documented in detail in Getsinger et al. (J. Fluid Mech., vol. 760, 2014, pp. 342-367), and the jet's mixing characteristics, consistent with diffusion-dominated processes, but with a few notable exceptions. When quantified as a function of distance along the jet trajectory, mixing metrics for jets in cross-flow with an absolutely unstable upstream shear layer and relatively symmetric counter-rotating vortex pair cross-sectional structure tend to show better local molecular mixing than for jets with convectively unstable upstream shear layers and generally asymmetric cross-sectional structures. Yet the spatial evolution of mixing with downstream distance can be greater for a few specific convectively unstable conditions, apparently associated with the initiation and nature of shear layer rollup as a trigger for improved mixing. A notable exception to these trends concerns conditions where the equidensity jet in cross-flow has an upstream shear layer that is already absolutely unstable, and the jet density is then reduced in comparison with that of the cross-flow. Here, density ratios below unity tend to mix less well than for equidensity conditions, demonstrated to result from differences in the nature of higher-density cross-flow entrainment into lower-density shear layer vortices.

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“…Exceptions would include the case where the stoichiometric mixture fraction is dramatically different from the entrainment ratio of the shear layer, which would lead to a flame that resides on the either outside edge of the shear layer, or exhibiting asymmetry. [17][18][19] If the flame is located nominally within the shear layer and has similar thickness, the flame tends to stabilize the shear layer, although transition to absolute instability occurs at a similar level of counterflow. This provides encouragement that global instability may be achievable in reacting shear layers with realizable counterflow levels.…”

Section: Discussionmentioning

confidence: 99%

“…1070-6631/2014/26(5)/054102/11/$30.00 C 2014 AIP Publishing LLC 26, 054102-1 reduces entrainment, [17][18][19][20][21][22] there is an opportunity to use linear theory to identify reacting shear layer configurations that are absolutely unstable. A reacting shear layer in an absolute instability regime will likely have enhanced entrainment characteristics, providing an opportunity to increase combustion intensity.…”

Section: Introductionmentioning

confidence: 99%

On the influence of internal density variations on the linear stability characteristics of planar shear layers

Hajesfandiari

Forliti

2014

Physics of Fluids

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Articles you may be interested inObservation and modeling of mixing-layer development in high-energy-density, blast-wave-driven shear flowa) Phys. Plasmas 21, 056306 (2014);Planar shear layers are known to be sensitive to density variation within the vorticity region. The current study will expand on the available literature on the stability characteristics of shear layers with density variation through consideration of new regimes in terms of the velocity and density profiles. Both spatial and spatio-temporal linear analyses were considered. In addition to the maximum density change within the shear layer, the effect of density to vorticity thickness ratio, and transverse shifting of the density profile relative to the velocity profile were considered. For a shear layer experiencing combustion, these effects relate to the relative position and thickness of the flame in the shear layer. Thick density profiles have a stabilizing affect that imposes essentially a low-pass attenuator modulation on the spatial stability. The shear layer is destabilized through the presence of an intense yet thin density reduction that overlaps with the peak vorticity profile, a condition that may be present near the shear layer origination point. The velocity ratio at which the flow transitions between absolute and convective instability is dependent on the magnitude of the density reduction in the shear layer as well as the relative density profile thickness and transverse location. The results generally indicate that the instability of the planar shear layer is strongly influenced by the characteristics of the density-weighted vorticity distribution within the shear layer. C 2014 AIP Publishing LLC. [http://dx.

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Heat release effects on shear-layer growth and entrainment

Cited by 31 publications

References 21 publications

Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

Transverse jet mixing characteristics

On the influence of internal density variations on the linear stability characteristics of planar shear layers

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