3,119 research outputs found
Multiple-scale turbulence modeling of boundary layer flows for scramjet applications
As part of an investigation into the application of turbulence models to the computation of flows in advanced scramjet combustors, the multiple-scale turbulence model was applied to a variety of flowfield predictions. The model appears to have a potential for improved predictions in a variety of areas relevant to combustor problems. This potential exists because of the partition of the turbulence energy spectrum that is the major feature of the model and which allows the turbulence energy dissipation rate to be out of phase with turbulent energy production. The computations were made using a consistent method of generating experimentally unavailable initial conditions. An appreciable overall improvement in the generality of the predictions is observed, as compared to those of the basic two-equation turbulence model. A Mach number-related correction is found to be necessary to satisfactorily predict the spreading rate of the supersonic jet and mixing layer
Cosmology with Ricci-type dark energy
We consider the dynamics of a cosmological substratum of pressureless matter
and holographic dark energy with a cutoff length proportional to the Ricci
scale. Stability requirements for the matter perturbations are shown to single
out a model with a fixed relation between the present matter fraction
and the present value of the equation-of-state
parameter of the dark energy. This model has the same number of free parameters
as the CDM model but it has no CDM limit. We discuss the
consistency between background observations and the mentioned
stability-guaranteeing parameter combination.Comment: 6 pages, 3 figures, submitted to the Proceedings of the CosmoSurII
conference, Valpara\'iso, Chile, 27 - 31 May 201
Density perturbations in an Universe dominated by the Chaplygin gas
We study the fate of density perturbations in an Universe dominate by the
Chaplygin gas, which exhibit negative pressure. We show that it is possible to
obtain the value for the density contrast observed in large scale structure of
the Universe by fixing a free parameter in the equation of state of this gas.
The negative character of pressure must be significant only very recently.Comment: Latex file, 5 page
Generalized Chaplygin gas with and the cosmological model
The generalized Chaplygin gas model is characterized by the equation of state
. It is generally stated that the case is equivalent to a model with cosmological constant and dust (). In this work we show that, if this is true for the background equations,
this is not true for the perturbation equations. Hence, the mass spectrum
predicted for both models may differ.Comment: Latex file, 4 pages, 2 figures in eps forma
global monopole revisited
In this paper the global monopole is reexamined. We provide an exact
solution for the modified field equations in the presence of a global monopole
for regions outside its core, generalizing previous results. Additionally, we
discuss some particular cases obtained from this solution. We consider a setup
consisting of a possible Schwarzschild black hole that absorbs the topological
defect, giving rise to a static black hole endowed with a monopole's charge.
Besides, we demonstrate how the asymptotic behavior of the Higgs field far from
the monopole's core is shaped by a class of spacetime metrics which includes
those ones analyzed here. In order to assess the gravitational properties of
this system, we analyse the geodesic motion of both massive and massless test
particles moving in the vicinity of such configuration. For the material
particles we set the requirements they have to obey in order to experience
stable orbits. On the other hand, for the photons we investigate how their
trajectories are affected by the gravitational field of this black hole.Comment: 16 pages, 1 figure and 1 table. Minor changes to match published
version in EPJ
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