Symmetry concepts for the geometric analysis of mixing flows Franjione, J. G.; Ottino, J. M.; Smith, F. T.
Philosophical transactions of the Royal Society of London. Series A: Physical sciences and engineering,
02/1992, Letnik:
338, Številka:
1650
Journal Article
Recenzirano
Much of the recent analysis of chaotic mixing has focused on utilizing tools and techniques imported from dynamical systems theory. However, most techniques require detailed information about the ...velocity field or fluid motion and are restricted to conditions where the ‘degree of chaos’ is small. Symmetries provide a method of analysis without specific reference to exact mathematical expressions. Symmetry concepts are illustrated in terms of a prototypical system called the eggbeater flow. Although a family of 32 different eggbeater flows can be constructed, symmetry arguments reveal that only four of these are independent. These flows serve to illustrate the role of islands in mixing. If a flow possesses symmetry, islands are found in symmetric arrangements, the simplest cases being reflections and rotational symmetries. A knowledge of symmetries provides the basis for systematic methods for destroying islands. These ideas are developed in terms of the eggbeater flows, and are subsequently extended to a class of three-dimensional continuous throughput flows - duct flows - which are of a more practical interest from an engineering viewpoint. Three such duct flows are studied. Using symmetries, we show that these flows are topologically identical to the eggbeater flows, even though their geometries and flow mechanisms are quite different from the eggbeater flows. Lastly, we demonstrate how the same methodology for destroying islands and enhancing mixing in the eggbeater flows can be applied to duct flows.
Regulatory T cells (Tregs) modulate tissue homeostatic processes and immune responses. Understanding tissue-Treg biology will contribute to developing precision-targeting treatment strategies. Here, ...we show that Tregs maintain the tolerogenic state of the testis and epididymis, where sperm are produced and mature. We found that Treg depletion induces severe autoimmune orchitis and epididymitis, manifested by an exacerbated immune cell infiltration CD4 T cells, monocytes, and mononuclear phagocytes (MPs) and the development of antisperm antibodies (ASA). In Treg-depleted mice, MPs increased projections toward the epididymal lumen as well as invading the lumen. ASA-bound sperm enhance sperm agglutination and might facilitate sperm phagocytosis. Tolerance breakdown impaired epididymal epithelial function and altered extracellular vesicle cargo, both of which play crucial roles in the acquisition of sperm fertilizing ability and subsequent embryo development. The affected mice had reduced sperm number and motility and severe fertility defects. Deciphering these immunoregulatory mechanisms may help to design new strategies to treat male infertility, as well as to identify potential targets for immunocontraception.
Phys. Rev. C 107, 024907 (2023) Recently, the PHENIX Collaboration has published second- and third-harmonic
Fourier coefficients $v_2$ and $v_3$ for midrapidity ($|\eta|<0.35$) charged
hadrons in ...0\%--5\% central $p$$+$Au, $d$$+$Au, and $^3$He$+$Au collisions at
$\sqrt{s_{_{NN}}}=200$ GeV utilizing three sets of two-particle correlations
for two detector combinations with different pseudorapidity acceptance Phys.
Rev. C {\bf 105}, 024901 (2022). This paper extends these measurements of
$v_2$ to all centralities in $p$$+$Au, $d$$+$Au, and $^3$He$+$Au collisions, as
well as $p$$+$$p$ collisions, as a function of transverse momentum ($p_T$) and
event multiplicity. The kinematic dependence of $v_2$ is quantified as the
ratio $R$ of $v_2$ between the two detector combinations as a function of event
multiplicity for $0.5$$<$$p_T$$<$$1$ and $2$$<$$p_T$$<$$2.5$ GeV/$c$. A
multiphase-transport (AMPT) model can reproduce the observed $v_2$ in
most-central to midcentral $d$$+$Au and $^3$He$+$Au collisions. However, the
AMPT model systematically overestimates the measurements in $p$$+$$p$,
$p$$+$Au, and peripheral $d$$+$Au and $^3$He$+$Au collisions, indicating a
higher nonflow contribution in AMPT than in the experimental data. The AMPT
model fails to describe the observed $R$ for $0.5$$<$$p_T$$<$$1$ GeV/$c$, but
there is qualitative agreement with the measurements for $2$$<$$p_T$$<$$2.5$
GeV/$c$.
In numerical combustion applications the Flamelet Generated Manifolds technique (FGM) is being used at an increasingly number of occasions. This technique is an approach to reduce the chemistry ...efficiently and accurately. In the present work FGM is coupled to an OpenFOAM-based CFD solver. The multidimensional flame is described by an ensemble of 1D laminar flames generated through a 1D detailed chemistry solver, by taking into account both convective and diffusive contributions as well as the required source terms. The flame structure is parameterized as function of a progress variable and few controlling variables such as the variance of the progress variable and the enthalpy. A manifold, which collects the 1D flame properties, is built from the 1D flame solutions. For the progress variable and each controlling variable, a transport equation is added to the standard flow conservation equations. During runtime, key quantities are retrieved from the manifold by interpolation. The resulting FGM-CFD coupled code has two significant features: the ability to treat heat loss effects and the adoption of turbulence level to describe the flame structure, providing high quality numerical results within practical industrial configurations. In the present work, a backward-facing step configuration with a methane/air mixture is investigated. Some key aspects of reactive phenomena in standard industrial burner configurations, such as the recirculation region development and the flame stabilization, are considered here. Numerical simulations are performed comparing results with experiments available in literature (Banhawy et al. Combust. Flame
50
:153–165,
18
). Both RANS and LES approaches are adopted: improvements with respect to prior available works are highlighted. Moreover, LES data, available for the first time within this configuration, are used to provide a deeper insight of turbulence/combustion interaction.
By experiments and supporting computations we investigate two methods of transport
enhancement in two-dimensional open cellular flows with inertia. First, we introduce
a spatial dependence in the ...velocity field by periodic modulation of the shape of
the wall driving the flow; this perturbs the steady-state streamlines in the direction
perpendicular to the main flow. Second, we introduce a time dependence through
transient acceleration–deceleration of a flat wall driving the flow; surprisingly, even
though the streamline portrait changes very little during the transient, there is still
significant transport enhancement. The range of Reynolds and Reynolds–Strouhal
numbers studied is 7.7les Reles 46.5 and 0.52les ReSrles 12.55 in the spatially dependent
mode and 12les Reles 93 and 0.26les ReSrles 5.02 in the time-dependent mode.
The transport is described theoretically via lobe dynamics. For both modifications, a
curve with one maximum characterizes the various transport enhancement measures
when plotted as a function of the forcing frequency. A qualitative analysis suggests
that the exchange first increases linearly with the forcing frequency and then decreases
as 1/Sr for large frequencies.
Visualization of Three-Dimensional Chaos Fountain, G. O.; Khakhar, D. V.; Ottino, J. M.
Science (American Association for the Advancement of Science),
07/1998, Letnik:
281, Številka:
5377
Journal Article
Recenzirano
Most chaotic mixing experiments have been restricted to two-dimensional, time-periodic flows, and this has shaped advances in theory as well. A prototypical, bounded, three-dimensional flow with a ...moderate Reynolds number is presented; this system lends itself to detailed experimental observation and allows for high-precision computational inspection. The flow structure, captured by means of cuts with a laser sheet (experimental Poincaré section), was visualized with the use of continuously injected fluorescent dye streams and revealed detailed chaotic structures with high-period islands.
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