On the Influence of the Combustion Model on the Result of Turbulent Flames Numerical Simulations

2012 ◽  
Author(s):  
Bogdan Gherman ◽  
Florin Gabriel Florean ◽  
Cristian Cârlănescu ◽  
Ionuţ Porumbel
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Stokes Equations ◽  
Reaction Diffusion ◽  
Turbulent Flames ◽  
Reaction Diffusion Equations ◽  
Combustion Model ◽  
One Dimensional ◽  
Turbulent Reactive Flows ◽  
The Impact

The paper is aimed at evaluating the impact of the combustion model on the accuracy of the results of the numerical simulations of turbulent reactive flows. For this, two numerical simulations of the well known Sandia Flame D case are carried out: a three-dimensional RANS integration of the Navier–Stokes equations using the Eddy Dissipation combustion Model (EDM), and a one-dimensional one, where simplified reaction–diffusion equations are numerically integrated over the radial direction, while the axial convection is modeled by empirical laws. The one-dimensional simulation, however, is based on a more physics related combustion model, the Linear Eddy Mixing model, which also controls the radial turbulent mixing and the large scale radial convection. The results of the two numerical simulations are compared to experimental data in the literature, showing a significantly better accuracy of the Linear Eddy Mixing (LEM) numerical simulation.

scholarly journals Analytical and Numerical Feasibility Analysis of a Contra-Rotary Ramjet Engine

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 163
Author(s):  
Tomasz Laube ◽  
Janusz Piechna
Keyword(s):  
Numerical Simulations ◽  
Stokes Equations ◽  
Analytical Data ◽  
Combustion Process ◽  
Flow Characteristics ◽  
Combustion Model ◽  
Similar Data ◽  
High Rotational Speed ◽  
Jet Engine ◽  
Ramjet Engine

A new idea for a contra-rotary ramjet engine is presented. To define the theoretical limits of the non-typical, contra-rotary ramjet engine configuration, its analytical model was developed. The results obtained from that model and the analytical results were compared with those received from numerical simulations. The main weakness of existing rotary ramjet engine projects is the very high rotational speed of the rotor required for achieving supersonic inlet flow. In this paper, a new idea for a contra-rotary ramjet engine (CORRE) is presented and analyzed. This paper presents the results of analytical analysis and numerical simulations of a jet engine system with two rotors rotating in opposite directions. Contra-rotating rotors generate a supersonic air velocity at the inlet to the compressor at two times slower rotor’s speed. To determine the flow characteristics, combustion process, and engine efficiency of the double-rotor engine, a numerical solution of the average Navier-Stokes equations was used with the k-eps turbulence model and the non-premixed combustion model. The results of numerical simulations of flow and the combustion process inside the contra-rotary jet engine achieving a shockwave compression are shown and compared with similar data for a single-rotor engine design and analytical data. This paper presents only the calculation results of the flow processes and the combustion process, indicating the advantages of the proposed double-rotor design. The results of the numerical analysis were presented on the contours and diagrams of the pressure and flow velocity, temperature distribution, and mass fraction of the fuel.

A PARALLEL SOLVER FOR REACTION–DIFFUSION SYSTEMS IN COMPUTATIONAL ELECTROCARDIOLOGY

2004 ◽  
Vol 14 (06) ◽  
pp. 883-911 ◽  
Author(s):  
PIERO COLLI FRANZONE ◽  
LUCA F. PAVARINO
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Reaction Diffusion ◽  
Ionic Currents ◽  
Reaction Diffusion Equations ◽  
Reaction Diffusion Equation ◽  
Fiber Direction ◽  
Axially Symmetric ◽  
Reaction Diffusion Systems ◽  
Cardiac Model

In this work, a parallel three-dimensional solver for numerical simulations in computational electrocardiology is introduced and studied. The solver is based on the anisotropic Bidomain cardiac model, consisting of a system of two degenerate parabolic reaction–diffusion equations describing the intra and extracellular potentials of the myocardial tissue. This model includes intramural fiber rotation and anisotropic conductivity coefficients that can be fully orthotropic or axially symmetric around the fiber direction. The solver also includes the simpler anisotropic Monodomain model, consisting of only one reaction–diffusion equation. These cardiac models are coupled with a membrane model for the ionic currents, consisting of a system of ordinary differential equations that can vary from the simple FitzHugh–Nagumo (FHN) model to the more complex phase-I Luo–Rudy model (LR1). The solver employs structured isoparametric Q1finite elements in space and a semi-implicit adaptive method in time. Parallelization and portability are based on the PETSc parallel library. Large-scale computations with up to O(107) unknowns have been run on parallel computers, simulating excitation and repolarization phenomena in three-dimensional domains.

scholarly journals Can the Impact of Aerosols on Deep Convection be Isolated from Meteorological Effects in Atmospheric Observations?

2018 ◽  
Vol 75 (10) ◽  
pp. 3347-3363 ◽  
Author(s):  
Wojciech W. Grabowski
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Cloud Condensation Nuclei ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Phase Iii ◽  
Moist Convection ◽  
Atmospheric Measurements ◽  
The Impact ◽  
Meteorological Effects

Influence of pollution on dynamics of deep convection continues to be a controversial topic. Arguably, only carefully designed numerical simulations can clearly separate the impact of aerosols from the effects of meteorological factors that affect moist convection. This paper argues that such a separation is virtually impossible using observations because of the insufficient accuracy of atmospheric measurements and the fundamental nature of the interaction between deep convection and its environment. To support this conjecture, results from numerical simulations are presented that apply modeling methodology previously developed by the author. The simulations consider small modifications, difficult to detect in observations, of the initial sounding, surface fluxes, and large-scale forcing tendencies. All these represent variations of meteorological conditions that affect deep convective dynamics independently of aerosols. The setup follows the case of daytime convective development over land based on observations during the Large-Scale Biosphere–Atmosphere (LBA) field project in Amazonia. The simulated observable macroscopic changes of convection, such as the surface precipitation and upper-tropospheric cloudiness, are similar to or larger than those resulting from changes of cloud condensation nuclei from pristine to polluted conditions studied previously using the same modeling case. Observations from Phase III of the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) are also used to support the argument concerning the impact of the large-scale forcing. The simulations suggest that the aerosol impacts on dynamics of deep convection cannot be isolated from meteorological effects, at least for the daytime development of unorganized deep convection considered in this study.

Reflood Oxidation Model Based on Reaction-Diffusion Equations

2010 ◽  
Author(s):  
Xiaoqiang He ◽  
Hongxing Yu ◽  
Guangming Jiang
Keyword(s):  
Metal Layer ◽  
Reaction Diffusion ◽  
Reaction Diffusion Equations ◽  
Diffusion Equations ◽  
Severe Accident ◽  
Model Based ◽  
Oxidation Model ◽  
The Impact ◽  
Relap5 Code ◽  
Good Agreement

An important accident management measure in PWRs is the injection of water to cool the degrading core, in which process the temperature and hydrogen production will significantly increase due to enhanced oxidation after shattering of zircaloy fuel rod. This phenomenon can be described by Zr oxidation model and shattering model. The process of Zr oxidation is usually represented by parabolic rate correlations. But, after consumption of primary β-Zr, or in steam starvation conditions, the correlation approach is restricted. Besides, using this approach, it is impossible to obtain detailed oxygen distribution in the cladding which impacts the detailed mechanical behavior, such as shattering of cladding. The shattering of cladding is mainly contributed by deep cracks penetrating the oxide layer as well as the adjacent metallic. In SCDAP/RELAP5, the shattering criterion is relevant to the thickness of β-Zr, the cladding temperature, and the cooldown rate. After shattering of cladding, the oxide scale is simply removed. This shattering criterion deviates from the experiment of Chung and Kassner when the maximum cladding temperature exceeds 1560 K, and the model can’t reveal the impact of the cladding surface temperature before cooldown on cladding conditions after shattered. An oxidation model based on reaction-diffusion equations at the temperature range from 923K to 2098K is developed in this study. By comparison with experimental data, the model shows reasonable results. Based on the oxidation model, the advanced shattering criterion is adopted, and a new empirical model to describe the cladding conditions after shattered is proposed. In present shattering model, R(T, m), which is the ratio between the area of new crack surfaces in the metal layer and the area of outer cladding surface, is the function of T (the temperature of the cladding surface before cooldown) and m (the thickness of the metal layer). With the help of single-rod QUENCH experiment, the preliminary expression of R(T, m) is obtained, and the results are in a good agreement qualitatively with the observation in this experiment. Further activities should focus on the impact of m and T on R(T, m), which needs more detailed single-rod experiments. Those developed models can be implemented into the SCDAP/RELAP5 code easily and used in the severe accident analysis in the future.

scholarly journals T-ReX: a graph-based filament detection method

2020 ◽  
Vol 637 ◽  
pp. A18 ◽  
Author(s):  
Tony Bonnaire ◽  
Nabila Aghanim ◽  
Aurélien Decelle ◽  
Marian Douspis
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Spanning Trees ◽  
Filamentary Structure ◽  
Underlying Distribution ◽  
Galaxy Surveys ◽  
Automatic Retrieval ◽  
Diffuse Part ◽  
Distribution Of Points ◽  
The Impact

Numerical simulations and observations show that galaxies are not uniformly distributed in the universe but, rather, they are spread across a filamentary structure. In this large-scale pattern, highly dense regions are linked together by bridges and walls, all of them surrounded by vast, nearly-empty areas. While nodes of the network are widely studied in the literature, simulations indicate that half of the mass budget comes from a more diffuse part of the network, which is made up of filaments. In the context of recent and upcoming large galaxy surveys, it becomes essential that we identify and classify features of the Cosmic Web in an automatic way in order to study their physical properties and the impact of the cosmic environment on galaxies and their evolution. In this work, we propose a new approach for the automatic retrieval of the underlying filamentary structure from a 2D or 3D galaxy distribution using graph theory and the assumption that paths that link galaxies together with the minimum total length highlight the underlying distribution. To obtain a smoothed version of this topological prior, we embedded it in a Gaussian mixtures framework. In addition to a geometrical description of the pattern, a bootstrap-like estimate of these regularised minimum spanning trees allowed us to obtain a map characterising the frequency at which an area of the domain is crossed. Using the distribution of halos derived from numerical simulations, we show that the proposed method is able to recover the filamentary pattern in a 2D or 3D distribution of points with noise and outliers robustness with a few comprehensible parameters.

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