Numerical Simulation Of Reactive Flow Research Articles

Numerical Simulation of Reactive Flow in Fractured Carbonate Rocks during Acidization Based on Embedded Discrete Fracture Model

Numerical Simulation of Reactive Flow in Fractured Carbonate Rocks during Acidization Based on Embedded Discrete Fracture Model

Impact of the Partitioning Method on Multidimensional Adaptive-Chemistry Simulations

The large number of species included in the detailed kinetic mechanisms represents a serious challenge for numerical simulations of reactive flows, as it can lead to large CPU times, even for relatively simple systems. One possible solution to mitigate the computational cost of detailed numerical simulations, without sacrificing their accuracy, is to adopt a Sample-Partitioning Adaptive Reduced Chemistry (SPARC) approach. The first step of the aforementioned approach is the thermochemical space partitioning for the generation of locally reduced mechanisms, but this task is often challenging because of the high-dimensionality, as well as the high non-linearity associated to reacting systems. Moreover, the importance of this step in the overall approach is not negligible, as it has effects on the mechanisms’ level of chemical reduction and, consequently, on the accuracy and the computational speed-up of the adaptive simulation. In this work, two different clustering algorithms for the partitioning of the thermochemical space were evaluated by means of an adaptive CFD simulation of a 2D unsteady laminar flame of a nitrogen-diluted methane stream in air. The first one is a hybrid approach based on the coupling between the Self-Organizing Maps with K-Means (SKM), and the second one is the Local Principal Component Analysis (LPCA). Comparable results in terms of mechanism reduction (i.e., the mean number of species in the reduced mechanisms) and simulation accuracy were obtained for both the tested methods, but LPCA showed superior performances in terms of reduced mechanisms uniformity and speed-up of the adaptive simulation. Moreover, the local algorithm showed a lower sensitivity to the training dataset size in terms of the required CPU-time for convergence, thus also being optimal, with respect to SKM, for massive dataset clustering tasks.

Numerical Simulation of Reactive Flow of Two Turbulence Models Based on Probability Density Function

Numerical Simulation of Reactive Flow of Two Turbulence Models Based on Probability Density Function

Modelling compression ignition engines by incorporation of the flamelet generated manifolds combustion closure

Tabulated chemistry models allow to include detailed chemistry effects at low cost in numerical simulations of reactive flows. Characteristics of the reactive fluid flows are described by a reduced set of parameters that are representative of the flame structure at small scales so-called flamelets. For a specific turbulent combustion configuration, flamelet combustion closure, with proper formulation of the flame structure can be applied. In this study, flamelet generated manifolds (FGM) combustion closure with progress variable approach were incorporated with OpenFOAM® source code to model combustion within compression ignition engines. For IC engine applications, multi-dimensional flamelet look-up tables for counter flow diffusive flame configuration were generated. Source terms of non-premixed combustion configuration in flamelet domain were tabulated based on pressure, temperature of unburned mixture, mixture fraction, and progress variable. A new frozen flamelet method was introduced to link one dimensional reaction diffusion space to multi-dimensional Computational Fluid Dynamics (CFD) physical space to fulfill correct modelling of thermal state of the engine at expansion stroke when charge composition was changed after combustion and reaction rates were subsided. Predictability of the developed numerical framework were evaluated for Sandia Spray A (constant volume vessel), Spray B (light duty optical Diesel engine), and a heavy duty Diesel engine experiments under Reynolds averaged Navier Stokes turbulence formulation. Results showed that application of multi-dimensional FGM combustion closure can comprehensively predict key parameters such as: ignition delay, in-cylinder pressure, apparent heat release rate, flame lift-off , and flame structure in Diesel engines.

Numerical modelling and analysis of reactive flow and wormhole formation in fractured carbonate rocks

Combining the two-scale continuum model and the discrete fracture network model, a continuum-based model is developed that calculates the reactive flow of acid in carbonate rock with a complex fracture network. The locations of fractures in the model are explicitly defined and the method can capture complex geometric relationships. The governing equations are discretized by the finite-volume method, where the diffusion term and convection term are discretized using the two-point flux approximation (TPFA) scheme and the upwind scheme, respectively. The physical domain is discretized by Delaunay triangulation. To keep the robustness and efficiency of the TPFA scheme, the optimization algorithm is used to move the centroid node of the control volume to improve the orthogonality of the grids. Numerical simulations of reactive flow in 2D fractured porous media, in cases with simple and complex fracture arrays, under linear and radial flow conditions, are presented. In particular, a sensitivity analysis of the dissolution process with respect to the presence of fractures, fracture aperture, fracture distribution, and acid injection rate, is conducted.

A three-dimensional mathematical model for the anode of a direct ethanol fuel cell

In this paper, we develop a mathematical model to analyze a direct ethanol fuel cell (DEFC). The three-dimensional model is able to predict the flow on all layers of the fuel cell and allow a better analysis of physical and chemical phenomena that occur inside it. In addition, the calculation of mole fraction of species allows one to observe that the diffusion layer has great influence on mass transfer of fuel between the input channel and the catalyst layer. Numerical simulation of reactive flow was made based on the central finite difference method. The equations were integrated in time using the simplified Runge-Kutta multistage scheme. The results obtained are in agreement with the experimental data found in the literature, for different feed concentrations of ethanol and for different operating temperatures of the cell. In this way, the paper contributes to the development of a model for direct ethanol fuel cells, taking into account all losses overpotentials at the anode and the cathode, providing a better understanding of the physical and chemical behavior inside the cell, and on the conversion of chemical energy into electrical energy.

Impact of variable geometry combustor on performance and emissions from miniature gas turbine engine

The scope of this study is the experimental and theoretical research into the developed concept of variable geometry combustion chamber for miniature gas turbine engine. The aims are to investigate the combustion performance and NOX/CO emissions from combustion chamber and to demonstrate advantages of proposed design over standard, fixed geometry combustor.Experimental studies were performed on a specially designed miniature combustion chamber test stand. Standard GTM-120 combustion chamber and proposed combustion chamber with variable dilution holes area were tested. Pressures and temperatures at main combustion sections as well as NOX and CO concentrations in exhaust gases were measured.Theoretical studies involve numerical simulations of reactive flow inside standard and variable geometry combustion chambers. Detailed chemical kinetic mechanisms were used to describe the chemistry involved in the combustion process. The outputs from numerical simulations are coupled with a reduced system represented by cylindrical share flow reactor model in order to examine the impact of the gas analyzer probe and hose on the composition of the exhaust gases.Results of theoretical studies are in good agreement with results obtained experimentally. Both show significant advantages of utilization of the variable geometry combustion chamber in terms of performance and emissions reduction. The NOX reduction by over 40% in comparison to standard geometry combustion chamber and double reduction in CO emissions for variable geometry combustor were noted. Additionally, the results are compared with real GTM-120 engine performance and emissions from bench testing [3]. Based on the experimental data, a set of 3-D performance and emissions maps has been created. The maps are aimed to aid for variable area dilution zone inside a small gas turbine engine control law creation.

Numerical Simulation of Reactive Flows in Ramjet Type Combustors and Associated Validation Experiments

Twenty years ago, a review listed the main challenges to overcome to accurately predict the reactive flow fields in ramjet combustion chambers. These issues were grouped into five topics: flow organization, combustion phenomena, stability and performance, unsteady combustion and heat transfer. The aim of this paper is to give a brief overview of the numerical and experimental studies that have been carried out since this inventory in the specific program named “Research Ramjet” to improve CFD codes. First, the experimental setup designed to obtain a better understanding and to build-up an experimental database in order to validate numerical simulations is described. Then, the progress made with regard to these technical issues is presented. Significant improvements came from the implementation of Large Eddy Simulations. However, some challenges still remain, including the prediction of the overall performance parameters and the combustion instabilities.

Numerical Simulation of Reactive Flows in Overexpanded Supersonic Nozzle with Film Cooling

Reignition phenomena occurring in a supersonic nozzle flow may present a crucial safety issue for rocket propulsion systems. These phenomena concern mainly rocket engines which use H2gas (GH2) in the film cooling device, particularly when the nozzle operates under over expanded flow conditions at sea level or at low altitudes. Consequently, the induced wall thermal loads can lead to the nozzle geometry alteration, which in turn, leads to the appearance of strong side loads that may be detrimental to the rocket engine structural integrity. It is therefore necessary to understand both aerodynamic and chemical mechanisms that are at the origin of these processes. This paper is a numerical contribution which reports results from CFD analysis carried out for supersonic reactive flows in a planar nozzle cooled with GH2film. Like the experimental observations, CFD simulations showed their ability to highlight these phenomena for the same nozzle flow conditions. Induced thermal load are also analyzed in terms of cooling efficiency and the results already give an idea on their magnitude. It was also shown that slightly increasing the film injection pressure can avoid the reignition phenomena by moving the separation shock towards the nozzle exit section.

Differential diffusion effects in numerical simulations of laminar, axi-symmetric H2/N2–air diffusion flames

The accuracy of a new methodology to include differential diffusion in numerical simulations of reactive flows is illustrated for a set of laminar, axi-symmetric H2/N2–air diffusion flames. From the comparison of the calculations with the experimental data it is observed that when differential diffusion effects are properly taken into account in the transport equations in physical space, simulation results agree well with the experimental data. Ignoring differential diffusion effects is not acceptable, due to lack of H2 diffusion close to the jet inlet. Overall, differential diffusion has a strong influence on the stabilization of the flame as well as on the chemical species concentrations.

Simulation of Viscous and Reactive Hypersonic Flows Behaviour in a Shock Tube Facility: TVD Schemes and Flux Limiters Application

Work performed in this study concerns mainly the analysis and the wisely use of TVD type schemes (total variation diminishing) for numerical simulation of reactive flows, these schemes are first presented in scalar equation. Their extension to Euler equations for a reactive gas mixture is conducted through the approximate extended solver of Riemann problem. A comparative study of specific variants of TVD schemes has been made in the case of one-dimensional unsteady flow for an inert and reactive gas mixture, which represents the classical instance of a shock tube. The purpose of this investigation is to highlight the general behaviour (order of accuracy) and performance of TVD schemes with various flux limiters for the simulation of reactive flows and in particular, to make possible the capture of the shock wave together with waves expansion for choosing the appropriate scheme to apply eventually in simulation of hypersonic viscous flow in chemical non equilibrium.

Numerical simulation of reactive flow in non-equilibrium behind a strong shock wave during re-entry into earth’s atmosphere

In this paper, we study the phenomena of thermo-chemical imbalance in a reactive mono-dimensional flow composed of a mixture of (79% nitrogen N2 and 21% oxygen O2 ). We are interested in modeling the physicochemical process that may be encountered in hypersonic flows, as vibrational excitation, dissociation and ionization, also the formation of chemical species to higher temperatures behind a detached strong shock. We put a special emphasis on vibrational relaxation model of CVD coupling. At these high temperatures, collisions electrons-atoms become very effective, taking in account the radiation that requires knowledge and modeling of all physicochemical processes (collisional and radiative). The mathematical model of flows at the atmospheric reentry is governed by Euler stationary equations coupled with the chemical kinetics and the radiative transfer equations. Our computational code is based on the finite differences method that used to discretize and resolve the obtained numerical model, where an appropriate mesh is selected in the relaxation zone in order to determine the flow parameters at each grid position

A dynamic adaptive chemistry scheme with error control for combustion modeling with a large detailed mechanism

A new error controlled dynamic adaptive chemistry (EC-DAC) scheme is developed and validated for ignition and combustion modeling with large, detailed, and comprehensively reduced n-heptane and n-decane mechanisms. A fuel oxidation progress variable is introduced to determine the local model reduction threshold by using the mass fraction of oxygen. An initial threshold database for error control is created according to the progress variable in a homogeneous ignition system using a detailed mechanism. The threshold database tabulated by the fuel oxidation progress variable is used to generate a dynamically reduced mechanism with a specified error bound by using the Path Flux Analysis (PFA) method. The method leads to an error-controlled kinetic model reduction according to the local mixture reactivity and improves the computation efficiency. Numerical simulations of the homogeneous ignition of n-heptane/air and n-decane/air mixtures at different initial conditions are conducted with one detailed and one comprehensively reduced mechanism involving 1034 and 121 species, respectively. The results show that the present algorithm of error-controlled adaptive chemistry scheme is accurate. The computation efficiency is improved by more than one-order for both mechanisms. Moreover, unsteady simulations of outwardly propagating spherical n-heptane/air premixed flames demonstrate that the method is rigorous even when transport is included. The successful validation in both ignition and unsteady flame propagation for both detailed and reduced mechanisms demonstrates that this method can be efficiently used in the direct numerical simulation of reactive flow for large kinetic mechanisms.

Equivalent Reaction Constant for Isothermal Reactive Flow with Power-Law Kinetics

The scale difference between chemical reactions and diffusive processes makes the numerical simulation of reactive flows a challenging task. The subscale effects of reactions are hard to capture unless the computational expenses of very fine-grid numerical simulations can be tolerated, which is not practically feasible. A solution is to develop methodologies to account for small-scale effects using coarse-grid simulations. In this article, an equivalent reaction constant for steady-state and isothermal reactive flow with a power-law kinetics is developed. The effects of Peclet number, Thiele modulus, and reaction order are investigated.

Anomalous Reactive Transport in the Framework of the Theory of Chromatography

The anomalous reactive transport considered here is the migration of contaminants through strongly sorbing permeable media without significant retardation. It has been observed in the case of heavy metals, organic compounds, and radionuclides, and it has critical implications on the spreading of contaminant plumes and on the design of remediation strategies. Even in the absence of the well-known fast migration pathways, associated with fractures and colloids, anomalous reactive transport arises in numerical simulations of reactive flow. It is due to the presence of highly pH-dependent adsorption and the broadening of the concentration front by hydrodynamic dispersion. This leads to the emergence of an isolated pulse or wave of a contaminant traveling at the average flow velocity ahead of the retarded main contamination front. This wave is considered anomalous because it is not predicted by the classical theory of chromatography, unlike the retardation of the main contamination front. In this study, we use the theory of chromatography to study a simple pH-dependent surface complexation model to derive the mathematical framework for the anomalous transport. We analyze the particular case of strontium (Sr2+) transport and define the conditions under which the anomalous transport arises. We model incompressible one-dimensional (1D) flow through a reactive porous medium for a fluid containing four aqueous species: H+, Sr2+, Na+, and Cl−. The mathematical problem reduces to a strictly hyperbolic 2 × 2 system of conservation laws for effective anions and Sr2+, coupled through a competitive Langmuir isotherm. One characteristic field is linearly degenerate while the other is not genuinely nonlinear due to an inflection point in the pH-dependent isotherm. We present the complete set of analytical solutions to the Riemann problem, consisting of only three combinations of a slow wave comprising either a rarefaction, a shock, or a shock–rarefaction with fast wave comprising only a contact discontinuity. Highly resolved numerical solutions at large Peclet numbers show excellent agreement with the analytic solutions in the hyperbolic limit. In the Riemann problem, the anomalous wave forms only if: hydrodynamic dispersion is present, the slow wave crosses the inflection locus, and the effective anion concentration increases along the fast path.

Numerical simulation of reactive flow in liquid composite molding using flux-corrected transport (FCT) based finite element/control volume (FE/CV) method

The mold-filling simulation of liquid composite molding (LCM) is of great importance in optimizing this cost-effective polymer-composites manufacturing process. The flow in LCM is a convection-dominated reactive, non-isothermal flow involving a moving boundary, so the Galerkin finite element method (FEM) has to be adapted with stabilization techniques to solve such problems. The streamline-upwind Petrov–Galerkin (SUPG) method is one of the most popular stabilized methods. However, the use of SUPG still leads to localized numerical wiggles in the vicinity of sharp solution gradients, which is often encountered in the 3D mold-filling simulation of LCM for thick parts. In this study, we propose to use the flux-corrected transport (FCT) based FEM to solve a set of highly convective transport equations. The numerical examples presented in this paper demonstrate the excellent performance of FCT based FEM in suppressing spurious oscillations in the regions of steep solution-gradients as opposed to the numerical instability of SUPG in such regions. For the first time, the FCT based FEM combined with the control-volume method is employed to simulate the non-isothermal mold-filling process in LCM. We have developed a simulation code PORE-FLOW© based on the scheme proposed in the study. Numerical studies have proven the stability of the FCT based FEM while modeling the mold-filling process of LCM.

Computational analysis of an instantaneous chemical reaction in a T‐microreactor

AbstractWe extend and apply a method for the numerical computation of convective and diffusive mixing in liquid systems with very fast irreversible chemical reaction to the case of unequal diffusivities. This approach circumvents the solution of stiff differential equations and, hence, facilitates the direct numerical simulation of reactive flows with quasi‐instantaneous reactions. The method is validated by means of a neutralization reaction which is studied in a T‐shaped micromixer and compared with existing experimental LIF‐data. Because of their large are‐to‐volume ratio, microreactors are well suited for fast chemical reactions which are seriously affected by the slow diffusive transport in aqueous media. Numerical computations for different reactor dimensions reveal the fact that, in a dimensionless setting, the obtained conversion is independent of the reactor size, if the flow conditions are the same. This corresponds to an increase of space‐time‐yield proportional to the square of the inverse scale factor. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Numerical simulation of pore space clogging in geothermal reservoirs by precipitation of anhydrite

Anhydrite cementation in hydrothermal reservoirs can decrease porosity and permeability significantly. In these cases, the amount of hot water produced by hydrothermal heat mining installations is far too low for an economical use of the resource. We study two such cases in the North German sedimentary basin where a secondary anhydrite cementation drastically reduced the original high permeability of a Rhaetian sandstone reservoir. Core-flooding experiments under reservoir conditions indicate that in contrast to the instant dissolution of anhydrite in saline reservoirs, the nucleation probability of anhydrite and the speed of epitaxy on anhydrite crystals ( 10 s - 1 m - 3 and 5 × 10 - 12 m 4 mol - 1 s - 1 , respectively) are very low. We performed numerical simulations of reactive flow on the local and regional scale in order to understand the apparent conflict between constricted nucleation, observed in laboratory experiments, and a complete filling of the pore space by anhydrite cementation found in core samples from boreholes at Neuruppin and Allermöhe. A highly resolved cylindrical reservoir model was used to simulate a chemical stimulation of the Allermöhe reservoir, i.e. the forced increase in porosity and permeability around the borehole in response to the injection of cold brines. Studying the dissolution process for different brine temperatures and salinities, we found that an injection of 5600 m 3 cold, highly saline brines will break through a cemented barrier of a radius of 5 m around the borehole after 10 days of stimulation. An additional study of the combined effect of hydraulic fracturing and chemical stimulation showed that both types of borehole stimulation increase the permeability by approximately the same amount if dissolution can act directly on the fracture walls. On the reservoir scale, numerical simulations indicate that strata-bound convective flow in the Rhaetian reservoir, driven by temperature differences due to the topography of the aquifer, is insufficient to explain the observed high degree of cementation. However, it can be shown that Ca 2 + and SO 4 2 - dissolved in the reservoir brine are forced to precipitate around the fracture zone, if additional hot fluids flow up along faults, heat up the aquifer, and mix with the colder reservoir brine.

Numerical Simulations of Reactive Flow in Hot Aquifers

In recent years, there has been a significant expansion in our ability to model systems that involve the interaction of fluid flow, mass transport, heat transfer, and geochemical reaction in porous media. Such scenarios arise in studies of both fundamental science, such as the effects of thermohaline flow and heat transfer in rift basins, and in the solution of applied problems, such as the response of a geothermal reservoir to the re‐injection of cool water. Numerical Simulation of Reactive Flow in Hot Aquifers presents the simulation tools that were developed by a team of researchers based in Germany.This group has a long history in analyzing geothermal systems, but the methods presented can be applied far beyond the study of geothermal reservoirs. The heart of the book is a description of the model SHEMAT. The executable code and a graphical user interface are included with the book.

Buchbesprechung: Numerical Simulation of Reactive Flow. Von E. S. Oran, J. P. Boris

Chemie Ingenieur TechnikVolume 74, Issue 4 p. 476-476 Buchbesprechung Buchbesprechung: Numerical Simulation of Reactive Flow. Von E. S. Oran, J. P. Boris D. Mewes, D. MewesSearch for more papers by this author D. Mewes, D. MewesSearch for more papers by this author First published: 18 April 2002 https://doi.org/10.1002/1522-2640(200204)74:4<476::AID-CITE476>3.0.CO;2-SAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume74, Issue4April, 2002Pages 476-476 RelatedInformation