6,196 research outputs found
Analytical Study of Gravity Effects on Laminar Diffusion Flames
A mathematical model is presented for the description of axisymmetric laminar-jet diffusion flames. The analysis includes the effects of inertia, viscosity, diffusion, gravity and combustion. These mechanisms are coupled in a boundary layer type formulation and solutions are obtained by an explicit finite difference technique. A dimensional analysis shows that the maximum flame width radius, velocity and thermodynamic state characterize the flame structure. Comparisons with experimental data showed excellent agreement for normal gravity flames and fair agreement for steady state low Reynolds number zero gravity flames. Kinetics effects and radiation are shown to be the primary mechanisms responsible for this discrepancy. Additional factors are discussed including elipticity and transient effects
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
Superdiffusion in the Dissipative Standard Map
We consider transport properties of the chaotic (strange) attractor along
unfolded trajectories of the dissipative standard map. It is shown that the
diffusion process is normal except of the cases when a control parameter is
close to some special values that correspond to the ballistic mode dynamics.
Diffusion near the related crisises is anomalous and non-uniform in time: there
are large time intervals during which the transport is normal or ballistic, or
even superballistic. The anomalous superdiffusion seems to be caused by
stickiness of trajectories to a non-chaotic and nowhere dense invariant Cantor
set that plays a similar role as cantori in Hamiltonian chaos. We provide a
numerical example of such a sticky set. Distribution function on the sticky set
almost coincides with the distribution function (SRB measure) of the chaotic
attractor.Comment: 10 Figure
A mathematical model for jet engine combustor pollutant emissions
Mathematical modeling for the description of the origin and disposition of combustion-generated pollutants in gas turbines is presented. A unified model in modular form is proposed which includes kinetics, recirculation, turbulent mixing, multiphase flow effects, swirl and secondary air injection. Subelements of the overall model were applied to data relevant to laboratory reactors and practical combustor configurations. Comparisons between the theory and available data show excellent agreement for basic CO/H2/Air chemical systems. For hydrocarbons the trends are predicted well including higher-than-equilibrium NO levels within the fuel rich regime. Although the need for improved accuracy in fuel rich combustion is indicated, comparisons with actual jet engine data in terms of the effect of combustor-inlet temperature is excellent. In addition, excellent agreement with data is obtained regarding reduced NO emissions with water droplet and steam injection
Synthetic promoter elements obtained by nucleotide sequence variation and selection for activity
Statistics of real eigenvalues in Ginibre's Ensemble of random real matrices
The integrable structure of Ginibre's orthogonal ensemble of random matrices is looked at through the prism of the probability pn,k to find exactly k real eigenvalues in the spectrum of an n×n real asymmetric Gaussian random matrix. The exact solution for the probability function pn,k is presented, and its remarkable connection to the theory of symmetric functions is revealed. An extension of the Dyson integration theorem is a key ingredient of the theory presented
Dynamics of the Chain of Oscillators with Long-Range Interaction: From Synchronization to Chaos
We consider a chain of nonlinear oscillators with long-range interaction of
the type 1/l^{1+alpha}, where l is a distance between oscillators and 0< alpha
<2. In the continues limit the system's dynamics is described by the
Ginzburg-Landau equation with complex coefficients. Such a system has a new
parameter alpha that is responsible for the complexity of the medium and that
strongly influences possible regimes of the dynamics. We study different
spatial-temporal patterns of the dynamics depending on alpha and show
transitions from synchronization of the motion to broad-spectrum oscillations
and to chaos.Comment: 22 pages, 10 figure
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