520 research outputs found
Obituary for Norbert Peters
Obituary for Norbert Peter
Source terms for calculations of vaporizing and burning fuel sprays with non-unity Lewis numbers in gases with temperature-dependent thermal conductivities
Liquid-fueled burners are used in a number of propulsion devices ranging from internal
combustion engines to gas turbines. The structure of spray flames is quite complex and
involves a wide range of time and spatial scales in both premixed and non-premixed
modes (Williams 1965; Luo et al. 2011). A number of spray-combustion regimes can be
observed experimentally in canonical scenarios of practical relevance such as counterflow
diffusion flames (Li 1997), as sketched in figure 1, and for which different microscalemodelling strategies are needed. In this study, source terms for the conservation equations are calculated for heating, vaporizing and burning sprays in the single-droplet combustion regime. The present analysis provides extended formulation for source terms, which include non-unity Lewis numbers and variable thermal conductivities
Numerical framework for transcritical real-fluid reacting flow simulations using the flamelet progress variable approach
An extension to the classical FPV model is developed for transcritical
real-fluid combustion simulations in the context of finite volume, fully
compressible, explicit solvers. A double-flux model is developed for
transcritical flows to eliminate the spurious pressure oscillations. A hybrid
scheme with entropy-stable flux correction is formulated to robustly represent
large density ratios. The thermodynamics for ideal-gas values is modeled by a
linearized specific heat ratio model. Parameters needed for the cubic EoS are
pre-tabulated for the evaluation of departure functions and a quadratic
expression is used to recover the attraction parameter. The novelty of the
proposed approach lies in the ability to account for pressure and temperature
variations from the baseline table. Cryogenic LOX/GH2 mixing and reacting cases
are performed to demonstrate the capability of the proposed approach in
multidimensional simulations. The proposed combustion model and numerical
schemes are directly applicable for LES simulations of real applications under
transcritical conditions.Comment: 55th AIAA Aerospace Sciences Meeting, Dallas, T
Combustion waves in a model with chain branching reaction and their stability
In this paper the travelling wave solutions in the adiabatic model with
two-step chain branching reaction mechanism are investigated both numerically
and analytically in the limit of equal diffusivity of reactant, radicals and
heat. The properties of these solutions and their stability are investigated in
detail. The behaviour of combustion waves are demonstrated to have similarities
with the properties of nonadiabatic one-step combustion waves in that there is
a residual amount of fuel left behind the travelling waves and the solutions
can exhibit extinction. The difference between the nonadiabatic one-step and
adiabatic two-step models is found in the behaviour of the combustion waves
near the extinction condition. It is shown that the flame velocity drops down
to zero and a standing combustion wave is formed as the extinction condition is
reached. Prospects of further work are also discussed.Comment: pages 32, figures 2
Short, synthetic and selectively 13C-labeled RNA sequences for the NMR structure determination of protein-RNA complexes
We report an optimized synthesis of all canonical 2′-O-TOM protected ribonucleoside phosphoramidites and solid supports containing [13C5]-labeled ribose moieties, their sequence-specific introduction into very short RNA sequences and their use for the structure determination of two protein-RNA complexes. These specifically labeled sequences facilitate RNA resonance assignments and are essential to assign a high number of sugar-sugar and intermolecular NOEs, which ultimately improve the precision and accuracy of the resulting structures. This labeling strategy is particularly useful for the study of protein-RNA complexes with single-stranded RNA in solution, which is rapidly an increasingly relevant research area in biolog
Short, synthetic and selectively 13C-labeled RNA sequences for the NMR structure determination of protein–RNA complexes
We report an optimized synthesis of all canonical 2′-O-TOM protected ribonucleoside phosphoramidites and solid supports containing [13C5]-labeled ribose moieties, their sequence-specific introduction into very short RNA sequences and their use for the structure determination of two protein–RNA complexes. These specifically labeled sequences facilitate RNA resonance assignments and are essential to assign a high number of sugar–sugar and intermolecular NOEs, which ultimately improve the precision and accuracy of the resulting structures. This labeling strategy is particularly useful for the study of protein–RNA complexes with single-stranded RNA in solution, which is rapidly an increasingly relevant research area in biology
Temperature and pollution control in flames
We apply control theory for PDEs to flame control. The targeted flame is calculated with complex chemistry. For pollutant control in flames we study both the control of temperature distribution in the flame and flame length at given fuel rate in the flow. Approximate state and sensitivity evaluations as well as mesh adaptation are used to keep the complexity as low as possible and get mesh independent results. In addition, a new recursive semi-deterministic global optimization approach is tested
Numerical generation of multidimensional flamelet databases using an adaptive wavelet method
The Wavelet Adaptive Multiresolution Representation (WAMR) code is used for the numerical time integration of the one-dimensional laminar diffusion flames equations in trans-critical and supercritical conditions, where the thermodynamic and transport properties exhibit large changes. These steep gradients are efficiently captured by the WAMR algorithm with an a-priori defined accuracy and an associated large reduction of the number of degrees of freedom, allowing a highly efficient flamelet database generation critical conditions
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