The retention factors in pure water for a homologous series of s-triazines were calculated by a numerical method basing on Ościk's equation and were correlated with log kw values obtained by linear and parabolic extrapolation. Chromatographic data (log kw) were compared with the software-calculated partition coefficients in the n-octanol/water system (Alog P, IAlog P, clog P, log PKowin, xlog P, log PACD and log PChem.Off.) as alternative hydrophobicity indices. The effect of organic modifier (methanol and acetonitrile) and its concentration in the mobile phase used for log kw evaluation were investigated. Very good linear correlations were found between log kw values calculated by the numerical method and log PACD, log PChem.Off. and clog P values, independent of organic modifier type.
This work investigates the structure of a diffusion flame in terms of lengthscales, scalar dissipation, and flame orientation by using large eddy simulation. This has been performed for a turbulent, non-premixed, piloted methane/air jet flame (Flame D) at a Reynolds-number of 22,400. A steady flamelet model, which was represented by artificial neural networks, yields species mass fractions, density, and viscosity as a function of the mixture fraction. This will be shown to suffice to simulate such flames. To allow to examine scalar dissipation, a grid of 1.97 × 106 nodes was applied that resolves more than 75% of the turbulent kinetic energy. The accuracy of the results is assessed by varying the grid-resolution and by comparison to experimental data by Barlow, Frank, Karpetis, Schneider (Sandia, Darmstadt), and others. The numerical procedure solves the filtered, incompressible transport equations for mass, momentum, and mixture fraction. For subgrid closure, an eddy viscosity/diffusivity approach is applied, relying on the dynamic Germano model. Artificial turbulent inflow velocities were generated to feature proper one- and two-point statistics. The results obtained for both the one- and two-point statistics were found in good agreement to the experimental data. The PDF of the flame orientation shows the tilting of the flame fronts towards the centerline. Finally, the steady flamelet approach was found to be sufficient for this type of flame unless slowly reacting species are of interest. 相似文献
In a two-phase flow the influence of a dispersed phase on the turbulence properties of a continuous phase, known as turbulence modification, is investigated. An experimental approach is discussed that is suitable for studying the decay of grid-generated turbulence in a vertically orientated wind tunnel with a cross-section large enough to avoid influences from walls. Phase Doppler anemometry is used to characterize both single and two-phase flow by measuring mean axial and radial velocity components, velocity fluctuations, turbulent kinetic energy, and integral time scales. By direct comparison of results from single- and two-phase flows, the feedback of the dispersed phase on the continuous phase can be isolated. The data is used to deduce a source term for particle-induced turbulence production appropriate for a numerical simulation of the flow, based on the Reynolds-averaged Navier-Stokes equations. Although of special importance for a detailed understanding of turbulent two-phase combustion, additional complexity introduced by evaporation and chemical reactions is avoided by using glass beads as dispersed phase. 相似文献
This study reports on experimental investigations on isothermal and reacting swirled non-premixed flows under varying pressure
conditions. In this configuration, a central high speed fuel jet was surrounded by a heated swirling air flow. For the reacting
case natural gas served as fuel whereas for isothermal conditions fuel was replaced by a mixture of helium and air to achieve
Reynolds-similarity. The optically accessible combustor allowed for application of laser diagnostics. Here we report on Laser
Doppler Anemometry and planar laser-induced fluorescence (PLIF) experiments used to characterize the flow field and visualize
selected scalars, respectively. Acetone served as a fluorescence marker for mixture fraction investigations. The hydroxyl
radical was used to provide general features of the reaction zone such as flame shape and mean stabilization. To expose the
influence of pressure on the flame structure three different operating points were investigated varying the combustor pressure
between 2 and 6 bar while the inflow bulk velocities remained the same. Striking features of the present configuration are
a detached flame, multiple recirculation zones, and complex coherent flow structures. 相似文献
In order to evaluate the direct and indirect contributions to the total combustion noise emission, a combustion chamber consisting
of a swirl burner and an exit nozzle of Laval-shape, representing a gas turbine combustor, is investigated by means of experiments
and large eddy simulation. Focused on the isothermal flow case first and encouraged by a good overall agreement between the
LES and the experimental data for the flow field, a first characterisation of the flow with respect to noise sources is performed.
To analyse acoustic properties of the flow, time and length scales are evaluated inside the combustor. Furthermore, the evidence
for the existence of a precessing vortex core (PVC), typical for configurations with swirl, is revealed. Finally, the effect
of the PVC on the flow inside the Laval nozzle is discussed. 相似文献
Chimeric oligonucleotides with incorporated diastereomerically pure dinucleoside(3′,5′)-methylphosphonothioates and their oxo- and seleno- congeners of known absolute configuration are reported. The relation between stability of the hybrid duplexes with complementary DNA and RNA and their structure is analyzed in context of absolute configuration of the P-chiral internucleotide bonds. 相似文献
The inner structure, and the physical behaviour of turbulent premixed flames are usually described, and classified by means of the regime diagram introduced by Borghi and Peters. Thereby properties related to both the flame and the (turbulent) flow are considered. In this work a diagram valid for all physical regimes, comprising suitable requirements for laminar simulations, direct numerical simulation (DNS), large-eddy simulation (LES), and Reynolds averaging based numerical simulation (RANS) is proposed. In particular the diagram describes essential situations within the validity limits of the “Borghi, Peters diagram” which physical phenomena are resolved by the simulation, and which have to be modelled. This information is used for systematic classification of various models by suggesting specific models that are appropriate depending on the regime and numerical resolution, and may provide guidance for numerical simulation methods and model development in turbulent premixed combustion. This might help users as a guideline in choosing appropriate models for a given device, and numerical effort available. The regime diagram suggested by Pitsch and Duchamp de Lageneste, which includes DNS and LES by explicitely accounting for the numerical related variable filterwidth, emerges here as one of the special two-dimensional cases possible. In contrast to the generalized regime diagram, their diagram does not include laminar simulations, and RANS based considerations, while transition between wrinkled and corrugated flamelets is not clearly established. 相似文献