Coherent structures and turbulent molecular mixing in gaseous planar shear layers

Meyer, Terrence R.; Dutton, J. C.; Lucht, Robert P.

doi:10.1017/s002211200600019x

Cited by 19 publications

(17 citation statements)

References 41 publications

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“…Using the cold-chemistry technique, where NOfluorescence is quenched when mixed with oxygen, Clemens and Paul [13] found values for the mixed fluid fraction of δ m /δ t = 0.45 at a convective Mach number of 0.35, and a value of δ m /δ t = 0.48 at a convective Mach number of 0.82. For top-stream velocities below 50 m/s, Meyer et al [16] found decreasing mixing with increasing top-stream velocity (Reynolds number) with values ranging from δ m /δ t = 0.58 at U 1 = 29.5 m/s and U 2 = 12.8 m/s to δ m /δ t = 0.55 at U 1 = 50.5 m/s and U 2 = 12.8 m/s using an improved dual-tracer cold-chemistry technique. These data show a decrease in mixing with increasing top-stream velocity that, if extrapolated, would give mixing efficiencies close to the fast-chemistry results.…”

Section: Mixing With Expansion-ramp Injectionmentioning

confidence: 99%

“…One flow geometry that can produce efficient mixing between two streams is the shear or mixing layer [5][6][7][8][9][10][11][12][13][14][15][16]. The geometry can be tailored to mitigate pressure gradients in the flow and minimize total-pressure losses.…”

Section: Introductionmentioning

confidence: 99%

“…However, such techniques cannot discriminate the amount of fluid that is mixed below the resolution of the optical system and detector [7,25] and measurements of passive scalar dispersion can overestimate the amount of molecular mixing in a gas by 40% [13], or more, in liquid-phase flows [7]. To compensate for spatial-resolution limitations of fluorescence techniques, investigators have taken advantage of the large quenching variation of NO fluorescence with the bath gas [13][14][15][16]. Collisional quenching of NO fluorescence acts similarly to a fast chemical reaction with no heat release and provides a measure of mixing on the molecular scale, similar to the chemically reacting "flip" experiment employed here.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Bergthorson

Johnson

Bonanos

et al. 2009

Flow Turbulence Combust

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The mixing and flowfield of a complex geometry, similar to a rearwardfacing step flow but with injection, is studied. A subsonic top-stream is expanded over a perforated ramp at an angle of 30 • , through which a secondary stream is injected. The mass flux of the second stream is chosen to be insufficient to provide the entrainment requirements of the shear layer, which, as a consequence, attaches to the lower guidewall. Part of the flow is directed upstream forming a re-entrant jet within the recirculation zone that enhances mixing and flameholding. A control-volume model of the flow is found to be in good agreement with the variation of the overall pressure coefficient of the device with variable mass injection. The flowfield response to changing levels of heat release is also quantified. While increased heat release acts somewhat analogously to increased mass injection, fundamental differences in the flow behaviour are observed. The hypergolic hydrogen-fluorine chemical reaction employed allows the level of molecular mixing in the flow to be inferred. The amount of mixing is found to be higher in the expansion-ramp geometry than in classical freeshear layers. As in free-shear layers, the level of mixing is found to decrease with increasing top-stream velocity. Results for a similar configuration with supersonic flow in the top stream are reported in Part II of this two-part series.

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Section: Mixing With Expansion-ramp Injectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Bergthorson

Johnson

Bonanos

et al. 2009

Flow Turbulence Combust

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show abstract

“…Experimental studies in the past 40 years acquired abundant evidence and data supporting the dynamical role of CS. CS control entrainment and mixing of species (Dimotakis & Brown 1976, Dutton & Lucht 2006, and contribute comparable amount to the Reynolds stresses and heat flux as does random turbulence (Hussain & Zaman 1985, Antonia et al 1986). The Reynolds stresses may take negative values in the region of positive mean-flow gradient, indicating that closure models of the mean-flow gradient type are inappropriate.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear dynamics of large-scale coherent structures in turbulent free shear layers

Zhuang

2015

J. Fluid Mech.

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Fully developed turbulent free shear layers exhibit a high degree of order, characterized by large-scale coherent structures in the form of spanwise vortex rollers. Extensive experimental investigations show that such organised motions bear remarkable resemblance to instability waves, and their main characteristics, including the length scales, propagation speeds and transverse structures, are reasonably well predicted by linear stability analysis of the mean flow. In this paper, we present a mathematical theory to describe the nonlinear dynamics of coherent structures. The formulation is based on the triple decomposition of the instantaneous flow into a mean field, coherent fluctuations and small-scale turbulence but with the mean-flow distortion induced by nonlinear interactions of coherent fluctuations being treated as part of the organised motion. The system is closed by employing gradient type of models for the time-and phase-averaged Reynolds stresses of fine-scale turbulence. In the high-Reynolds-number limit, the nonlinear non-equilibrium critical-layer theory for laminar-flow instabilities is adapted to turbulent shear layers by accounting for (a) the enhanced non-parallelism associated with fast spreading of the mean flow, and (b) the influence of small-scale turbulence on coherent structures. The combination of these factors with nonlinearity leads to an interesting evolution system, consisting of the coupled amplitude and vorticity equations, in which non-parallelism contributes the so-called translating critical-layer effect. Numerical solutions of the evolution system capture vortex roll-up, which is the hallmark of turbulent mixing layer, and the predicted amplitude development mimics the qualitative feature of oscillatory saturation that has been observed in a number of experiments. A fair degree of quantitative agreement is obtained with one set of experimental data.

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“…One of the most significant results is a detection of a sharp increase of mixing rates caused by the onset of small-scale turbulence within large-scale coherent motions [14]. This effect that was studied experimentally and numerically, demonstrates complex nonlinear dynamics of mixing (see, e.g., [8,11,15,16,17,18]). However, it is not clear how such mixing states are attained, and the ambiguity is exacerbated by the differences in experimental results.…”

Section: Introductionmentioning

confidence: 96%

Mixing at the External Boundary of a Submerged Turbulent Jet

Eidelman¹,

Elperin²,

Kleeorin³

et al. 2009

Springer Proceedings in Physics

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We study experimentally and theoretically mixing at the external boundary of a submerged turbulent jet. In the experimental study we use Particle Image Velocimetry and an Image Processing Technique based on the analysis of the intensity of the Mie scattering to determine the spatial distribution of tracer particles. An air jet is seeded with the incense smoke particles which are characterized by large Schmidt number and small Stokes number. We determine the spatial distributions of the jet fluid characterized by a high concentration of the particles and of the ambient fluid characterized by a low concentration of the tracer particles. In the data analysis we use two approaches, whereby one approach is based on the measured phase function for the study of the mixed state of two fluids. The other approach is based on the analysis of the two-point second-order correlation function of the particle number density fluctuations generated by tangling of the gradient of the mean particle number density by the turbulent velocity field. This gradient is formed at the external boundary of a submerged turbulent jet. We demonstrate that PDF of the phase function of a jet fluid penetrating into an external flow and the two-point second-order correlation function of the particle number density do not have universal scaling and cannot be described by a power-law function. The theoretical predictions made in this study are in a qualitative agreement with the obtained experimental results.

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Coherent structures and turbulent molecular mixing in gaseous planar shear layers

Cited by 19 publications

References 41 publications

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Nonlinear dynamics of large-scale coherent structures in turbulent free shear layers

Mixing at the External Boundary of a Submerged Turbulent Jet

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