365 research outputs found
Compressibility effects on the Rayleigh-Taylor instability growth between immiscible fluids
The linearized Navier-Stokes equations for a system of superposed immiscible
compressible ideal fluids are analyzed. The results of the analysis reconcile
the stabilizing and destabilizing effects of compressibility reported in the
literature. It is shown that the growth rate obtained for an inviscid,
compressible flow in an infinite domain is bounded by the growth rates obtained
for the corresponding incompressible flows with uniform and exponentially
varying density. As the equilibrium pressure at the interface
increases (less compressible flow), increases towards the uniform density
result, while as the ratio of specific heats increases (less
compressible fluid), decreases towards the exponentially varying density
incompressible flow result. This remains valid in the presence of surface
tension or for viscous fluids and the validity of the results is also discussed
for finite size domains. The critical wavenumber imposed by the presence of
surface tension is unaffected by compressibility. However, the results show
that the surface tension modifies the sensitivity of the growth rate to a
differential change in for the lower and upper fluids. For the viscous
case, the linearized equations are solved numerically for different values of
and . It is found that the largest differences compared with
the incompressible cases are obtained at small Atwood numbers. The most
unstable mode for the compressible case is also bounded by the most unstable
modes corresponding to the two limiting incompressible cases.Comment: To appear in Physics of Fluid
Non-premixed Flame-Turbulence Interaction in Compressible Turbulent Flow
Nonpremixed turbulent reacting flows are intrinsically difficult to model due
to the strong coupling between turbulent motions and reaction. The large amount
of heat released by a typical hydrocarbon flame leads to significant
modifications of the thermodynamic variables and the molecular transport
coefficients and thus alters the fluid dynamics. Additionally, in nonpremixed
combustion, the flame has a complex spatial structure. Localized expansions and
contractions occur, enhancing the dilatational motions. Therefore, the
compressibility of the flow and the heat release are intimately related.
However, fundamental studies of the role of compressibility on the scalar
mixing and reaction are scarce. In this paper we present results concerning the
fundamental aspects of the interaction between non-premixed flame and
compressible turbulence.Comment: 4 pages, 4 figures; to appear in Proceedings ETC9, Eds: I.P. Castro
and P.E. Hancock, CIMNE, Barcelona, 200
Learning to Embed Words in Context for Syntactic Tasks
We present models for embedding words in the context of surrounding words.
Such models, which we refer to as token embeddings, represent the
characteristics of a word that are specific to a given context, such as word
sense, syntactic category, and semantic role. We explore simple, efficient
token embedding models based on standard neural network architectures. We learn
token embeddings on a large amount of unannotated text and evaluate them as
features for part-of-speech taggers and dependency parsers trained on much
smaller amounts of annotated data. We find that predictors endowed with token
embeddings consistently outperform baseline predictors across a range of
context window and training set sizes.Comment: Accepted by ACL 2017 Repl4NLP worksho
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