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Manifold methods for methane combustion
Objective is to develop a new method for studying realistic chemistry in turbulent methane combustion with NO{sub x} mechanism. The realistic chemistry is a simplification to a more detailed chemistry based on the manifold method; accuracy is determined by interaction between the transport process and the chemical reaction. In this new (tree) method, probability density function or partially stirred reactor calculations are performed. Compared with the reduced mechanism, manifold, and tabulation methods, the new method overcomes drawbacks of the reduced mechanism method and preserves the advantages of the manifold method. Accuracy is achieved by specifying the size of the cell
Local existence of analytical solutions to an incompressible Lagrangian stochastic model in a periodic domain
We consider an incompressible kinetic Fokker Planck equation in the flat
torus, which is a simplified version of the Lagrangian stochastic models for
turbulent flows introduced by S.B. Pope in the context of computational fluid
dynamics. The main difficulties in its treatment arise from a pressure type
force that couples the Fokker Planck equation with a Poisson equation which
strongly depends on the second order moments of the fluid velocity. In this
paper we prove short time existence of analytic solutions in the
one-dimensional case, for which we are able to use techniques and functional
norms that have been recently introduced in the study of a related singular
model.Comment: 32 page
General relation for stationary probability density functions
A linear relation between a normalized, time (t) dependent, statistically stationary quantity (z) and the normalized conditional expectation (r) of â2z/ât2 allows r to generally satisfy two conditions subject to the stationarity requirement. Experimental data for both temperature and vorticity in several turbulent flows indicate that this relation appears universal. As a result, the exact expression derived by Pope and Ching [Phys. Fluids A 5, 1529 (1993)] for the probability density function (PDF) of any stationary quantity should generally reduce to the simpler form obtained by Ching [Phys. Rev. Lett. 70, 283 (1993)].J. Mi and R. A. Antoni
Predicting specific impulse distributions for spherical explosives in the extreme near-field using a Gaussian function
Accurate quantification of the blast load arising from detonation of a high explosive has applications in transport security, infrastructure assessment and defence. In order to design efficient and safe protective systems in such aggressive environments, it is of critical importance to understand the magnitude and distribution of loading on a structural component located close to an explosive charge. In particular, peak specific impulse is the primary parameter that governs structural deformation under short-duration loading. Within this so-called extreme near-field region, existing semi-empirical methods are known to be inaccurate, and high-fidelity numerical schemes are generally hampered by a lack of available experimental validation data. As such, the blast protection community is not currently equipped with a satisfactory fast-running tool for load prediction in the near-field. In this article, a validated computational model is used to develop a suite of numerical near-field blast load distributions, which are shown to follow a similar normalised shape. This forms the basis of the data-driven predictive model developed herein: a Gaussian function is fit to the normalised loading distributions, and a power law is used to calculate the magnitude of the curve according to established scaling laws. The predictive method is rigorously assessed against the existing numerical dataset, and is validated against new test models and available experimental data. High levels of agreement are demonstrated throughout, with typical variations of <5% between experiment/model and prediction. The new approach presented in this article allows the analyst to rapidly compute the distribution of specific impulse across the loaded face of a wide range of target sizes and near-field scaled distances and provides a benchmark for data-driven modelling approaches to capture blast loading phenomena in more complex scenarios
Yakhot's model of strong turbulence: A generalization of scaling models of turbulence
We report on some implications of the theory of turbulence developed by V.
Yakhot [V. Yakhot, Phys. Rev. E {\bf 57}(2) (1998)]. In particular we focus on
the expression for the scaling exponents . We show that Yakhot's
result contains three well known scaling models as special cases, namely K41,
K62 and the theory by V. L'vov and I. Procaccia [V. L'vov & I. Procaccia, Phys.
Rev. E {\bf 62}(6) (2000)]. The model furthermore yields a theoretical
justification for the method of extended self--similarity (ESS).Comment: 8 page
Numerical studies towards practical large-eddy simulation
Large-eddy simulation developments and validations are presented for an
improved simulation of turbulent internal flows. Numerical methods are proposed
according to two competing criteria: numerical qualities (precision and
spectral characteristics), and adaptability to complex configurations. First,
methods are tested on academic test-cases, in order to abridge with fundamental
studies. Consistent results are obtained using adaptable finite volume method,
with higher order advection fluxes, implicit grid filtering and "low-cost"
shear-improved Smagorinsky model. This analysis particularly focuses on mean
flow, fluctuations, two-point correlations and spectra. Moreover, it is shown
that exponential averaging is a promising tool for LES implementation in
complex geometry with deterministic unsteadiness. Finally, adaptability of the
method is demonstrated by application to a configuration representative of
blade-tip clearance flow in a turbomachine
When Does Eddy Viscosity Damp Subfilter Scales Sufficiently?
Large eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. The very essence is that the LES-solution contains only scales of size â„Î, where Î denotes some user-chosen length scale. This property enables us to perform a LES when it is not feasible to compute the full, turbulent solution of the Navier-Stokes equations. Therefore, in case the large eddy simulation is based on an eddy viscosity model we determine the eddy viscosity such that any scales of size <Î are dynamically insignificant. In this paper, we address the following two questions: how much eddy diffusion is needed to (a) balance the production of scales of size smaller than Î; and (b) damp any disturbances having a scale of size smaller than Î initially. From this we deduce that the eddy viscosity Îœe has to depend on the invariants q = Âœtr(S^2) and r =ââ
tr(S^3) of the (filtered) strain rate tensor S. The simplest model is then given by Îœe = 3/2(Î/Ï)^2|r|/q. This model is successfully tested for a turbulent channel flow (ReÏ = 590).
Brane-world Kaluza-Klein reductions and Branes on the Brane
We present a systematic study of a new type of consistent ``Brane-world
Kaluza-Klein Reduction,'' which describe fully non-linear deformations of
co-dimension one objects that arise as solutions of a large class of gauged
supergravity theories in diverse dimensions, and whose world-volume theories
are described by ungauged supergravities with one half of the original
supersymmetry. In addition, we provide oxidations of these Ansatze which are in
general related to sphere compactified higher dimensional string theory or
M-theory. Within each class we also provide explicit solutions of brane
configurations localised on the world-brane. We show that at the Cauchy horizon
(in the transverse dimension of the consistently Kaluza-Klein reduced
world-brane) there is a curvature singularity for any configuration with a
non-null Riemann curvature or a non-vanishing Ricci scalar that lives in the
world-brane. Since the massive Kaluza-Klein modes can be consistently
decoupled, they cannot participate in regulating these singularities.Comment: latex, 30 page
Path lengths in turbulence
By tracking tracer particles at high speeds and for long times, we study the
geometric statistics of Lagrangian trajectories in an intensely turbulent
laboratory flow. In particular, we consider the distinction between the
displacement of particles from their initial positions and the total distance
they travel. The difference of these two quantities shows power-law scaling in
the inertial range. By comparing them with simulations of a chaotic but
non-turbulent flow and a Lagrangian Stochastic model, we suggest that our
results are a signature of turbulence.Comment: accepted for publication in Journal of Statistical Physic
In vivo and in vitro proinflammatory effects of particulate air pollution (PM10).
Epidemiologic studies have reported associations between fine particulate air pollution, especially particles less than 10 mm in diameter (PM10), and the development of exacerbations of asthma and chronic obstructive pulmonary disease. However, the mechanism is unknown. We tested our hypothesis that PM10 induces oxidant stress, causing inflammation and injury to airway epithelium. We assessed the effects of intratracheal instillation of PM10 in rat lungs. The influx of inflammatory cells was measured in bronchoalveolar lavage (BAL). Airspace epithelial permeability was assessed as total protein in bronchoalveolar lavage fluid (BALF) in vivo. The oxidant properties of PM10 were determined by their ability to cause changes in reduced glutathione (GSH) and oxidized glutathione (GSSG). We also compared the effects of PM10 with those of fine (CB) and ultrafine (ufCB) carbon black particles. Six hours after intratracheal instillation of PM10, we noted an influx of neutrophils (up to 15% of total BAL cells) in the alveolar space, increased epithelial permeability, an increase in total protein in BALF from 0.39 +/- 0.01 to 0.62 +/- 0.01 mg/ml (mean +/- SEM) and increased lactate dehydrogenase concentrations in BALF. An even greater inflammatory response was observed after intratracheal instillation of ufCB, but not after CB instillation. PM10 had oxidant activity in vivo, as shown by decreased GSH in BALF (from 0.36 +/- 0.05 to 0.25 +/- 0.01 nmol/ml) after instillation. BAL leukocytes from rats treated with PM10 produced greater amounts of nitric oxide, measured as nitrite (control 3.07 +/- 0.33, treated 4.45 +/- 0.23 mM/1 x 10(6) cells) and tumor necrosis factor alpha (control 21.0 +/- 3.1, treated 179.2 +/- 29.4 unit/1 x 10(6) cells) in culture than BAL leukocytes obtained from control animals. These studies provide evidence that PM10 has free radical activity and causes lung inflammation and epithelial injury. These data support our hypothesis concerning the mechanism for the adverse effects of particulate air pollution on patients with airway diseases
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