Coupled Computational Fluid Dynamics Research Articles

CFD–DEM method is used to study the multi-phase coupling slag discharge flow field of gas-lift reverse circulation in drilling shaft sinking

To elucidate the distribution law of the multiphase coupling slag discharge flow field in gas-lift reverse circulation during drilling shaft sinking, a numerical analysis model of gas–liquid–solid multiphase coupling slag discharge was established by CFD–DEM (Coupling of computational fluid dynamics and discrete element method) method, taking the drilling of North Wind well in Taohutu Coal Mine as an example. This model presented the distribution of the multiphase flow field in the slag discharge pipe and at the bottom hole, and was validated through experimentation and theoretical analysis. Finally, the impact of factors, including bit rotation speed, gas injection rate, air duct submergence ratio, and mud viscosity on the slag discharge flow field was clarified. The results indicated that the migration of rock slag at the bottom of the well was characterized by “slip, convergence, suspension, adsorption, and lifting”. The slag flow in the discharge pipe exhibited the states of “high density, low flow rate” and “low density, high flow rate”, respectively. The multiphase fluid flow patterns in the well bottom and slag discharge pipe were horizontal and axial flows, respectively. The model test of the gas lift reversed circulation slag discharge and the theoretical model of the bottom hole fluid velocity distribution confirmed the accuracy of the multiphase coupling slag discharge flow field distribution model. The rotation speed of the drill bit had the most significant impact on the bottom hole flow field. Increasing the rotation speed of the drill bit can significantly enhance the tangential velocity of the bottom hole fluid, increase the pressure difference between the bottom hole and annular mud column, and improve the adsorption capacity of the slag suction port. These findings can provide valuable insights for gas lift reverse circulation well washing in western drilling shaft sinking.

Multiphase Numerical CFD Simulation of the Hydrothermal Liquefaction Process (HTL) of Sewage Sludge in a Tubular Reactor

This article presents multiphase numerical computational fluid dynamics (CFD) for simulating hydrothermal liquefaction of sewage sludge in a continuous plug-flow reactor. The discrete particle method (DPM) was used to analyze the solid particles’ interaction in liquid–solid high shear flows to investigate coupling computational fluid dynamics (CFD). Increasing solid particles’ interactions were observed with the increasing liquid velocity. The study examined the influence of parameters such as flow rate, temperature, and residence time on the efficiency of bio-oil production. An increase in temperature from 500 to 800 K caused an increase in the amount of biocrude oil produced from 12.4 to 32.9% within 60 min. In turn, an increase in the flow rate of the suspension from 10 to 60 mL/min caused a decrease in the amount of biocrude oil produced from 38.9 to 12.9%. This study offers insights into optimizing the flow channel of tubular reactors to enhance the HTL conversion efficiency of sewage sludge into biocrude oil. A parametric study was performed to investigate the effect of the slurry flow rate, temperature, and the external heat transfer coefficient on the biocrude oil production performance. The simulation data will be used in the future to design and scale up a large-scale HTL reactor.

Effects of CO2 Geosequestration on Opalinus Clay

CO2 geosequestration is an important contributor to United Nations Sustainable Development Goal 13, i.e., Climate Action, which states a global Net-Zero CO2 emissions by 2050. A potential impact of CO2 geosequestration in depleted oil and gas reservoirs is the variations in induced pressure across the caprocks, which can lead to significant local variations in CO2 saturation. A detailed understanding of the relationship between the pressure gradient across the caprock and local CO2 concentration is of utmost importance for assessing the potential of CO2 geosequestration. Achieving this through experimental techniques is extremely difficult, and thus, we employ a coupled Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) based solver to mimic sub-critical CO2 injection in Opalinus Clay under various pressure gradients across the sample. The geomechanical and multiphase flow modelling utilising Darcy Law helps evaluate local variations in CO2 concentration in Opalinus Clay. Well-validated numerical results indicate favourable sub-critical CO2 geosequestration under a positive pressure gradient across Opalinus Clay. In the absence of a positive pressure gradient, a peak CO2 concentration of 5% has been recorded, which increases substantially (above 90%) as the pressure gradient across the sample increases.

Swimming behaviour of downstream migrating carp in accelerating flows

The downstream migration of fish is impacted by accelerating flow. This study coupled computational fluid dynamics (CFD) modelling and laboratory observations to investigate the effects of two different accelerating flow hydrodynamics on the swimming behaviours of two fish species. The silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) were chosen as target fish species and four hydrodynamic parameters were selected as main indicators to affect fish swimming behaviours. Four specific swimming behaviours were classified in the contraction flume based on fish downstream trajectories. The results indicated that high accelerating flow, low turbulent kinetic energy (Tke ) and shear stress generated the symmetric distribution of fish along two boundaries of the contraction flume. It also indicated that discharge increase would increase the fish entrainment risk from intakes to diversion pipe, while two fish species exhibited different swimming behaviour patterns. Velocity and velocity gradient had more significant effects than other hydrodynamic parameters on fish swimming strategies. There was mutual compensation among fish tail-beat frequency, angle and amplitude. The results illustrated the relationship between the swimming behaviours and hydrodynamics, which could contribute to understanding the fish downstream migration behaviours in accelerating flow.

Detachment dynamics of sessile droplets triggered by interaction forces between oil and wall in a microchannel

Understanding the detachment dynamics of droplets adhered to reservoir walls holds significant importance for the residual oil displacement process in high water-cut oilfields. Existing studies demonstrated that increasing mainstream shear by adjusting displacement flow and weakening wall adhesion by increasing contact angle can enhance droplet detachment. However, the complex physical and chemical oil–wall interactions, a crucial reservoir feature, cannot be solely relied on the macroscopic representation through contact angle. A deviation in understanding the process of crude oil droplet detachment would be resulted due to the change of wall adhesion. Considering the intricate physical and chemical interactions between oil and walls, in this paper, we employed the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory to establish an oil–wall interaction forces system, and coupling computational fluid dynamics method to further explore the detachment dynamics of sessile oil droplets in a microchannel under varying EDLVO forces. The findings showed that (1) by increasing the Capillary number, the droplets gradually occur in four typical dynamic states: static, sliding, detachment, and pinch-off. (2) Static droplets are more prone to experience sliding behavior when influenced by EDLVO forces. (3) For droplets undergoing detachment and pinch-off, EDLVO forces inhibit entrainment behavior. These results contribute to an enhanced comprehension of droplet detachment dynamics in reservoirs, offering fresh insights for enhanced oil recovery strategies.

GPU-accelerated CFD-DEM modeling of gas-solid flow with complex geometry and an application to raceway dynamics in industry-scale blast furnaces

The coupling of Computational Fluid Dynamics (CFD) and Discrete Element Model (DEM) is a powerful tool for simulating dense particulate systems, yet the conventional CFD-DEM has limits for systems with large particle numbers and complex geometry. This paper reports a novel GPU-based CFD-DEM model to simulate the gas–solid flow with large particle numbers and complex geometry. A novel coupling strategy between the CFD solver and DEM solver is developed, featuring high efficiency and stability. The developed model is validated against the experimental measurements, and its efficiency is compared to the previous CFD-DEM simulations. Then, for demonstration, the model is employed to simulate the dynamic behavior of gas–solid flow in the raceway in ironmaking blast furnaces by considering complex tuyere structure details and the huge particle numbers involved. This model allows to study the effect of the tuyere angle in terms of raceway formulation and tuyere erosion. The results show that the largest and most stable raceway volume can be reached at 5° downward tuyere, although the −5° tuyere nose experiences more wear than 10° downward tuyere. The model provides a cost-effective tool to overcome the longstanding challenge of simulating dense fluid-particle systems with huge particle numbers and complex geometry.

Computational study of the Nitrogen-16 source term in the ITER vacuum vessel cooling circuit through the coupling of system-level analysis code and CFD

In ITER, the evaluation of the activated water radiation source and its impact on the radiological levels is necessary to demonstrate compliance with the safety requirements. The use of simplified or conservative approaches often results in the application of expensive constraints on the installation that impact its economics, operations, and construction schedule. In this work, we propose a novel methodology to calculate the activated water source term with a higher degree of realism. The methodology is based on the coupling of a system-level code with a Computational Fluid Dynamics (CFD) code in an explicit, one-way approach. We apply this methodology to the evaluation of the 16N radioisotope within the ITER Vacuum Vessel Primary Heat Transfer System (VV-PHTS) cooling circuit in a steady-state and transient scenarios. We chose this system since previous analyses of the VV-PHTS were done with simple, ad-hoc calculations that yielded results that differed by up to a factor of five, underscoring a higher level of uncertainty. As a result, we generate a computational model of the source term that can be used to evaluate the radiological condition surrounding the cooling systems during the operations.

Research on Structural Collapse of a Containership under Combined Bending–Torsion by Oblique Waves

Large waves cause a great number of collapsed-ship accidents, resulting in the loss of many lives and properties. It has been found that most of these collapses are caused by encountering oblique waves. As a result, the ship structure experiences a complex collapse under combined bending and torsion. This paper utilizes a numerical hydroelasto-plastic approach, coupling CFD (Computational Fluid Dynamics) with the nonlinear FEM (Finite-Element Method), to study the structural collapse of a containership in oblique waves. First, a 4600 TEU containership was selected to study its collapse mechanism under oblique waves. Second, a hydroelasto-plastic numerical coupling of CFD and nonlinear FEM is used to co-calculate the wave loads and structural collapse of containership. The hydrodynamic model is constructed and used to solve wave loads in the CFD solver, and a nonlinear FEM model of containership with finer meshes is also modeled to solve the structural collapses, including plasticity and buckling. Third, several oblique-wave cases involving heading angles of 120°, 135°, 150°, and 180° are determined and calculated. Typical cases are discussed for time-domain stress histories and collapsed courses. Finally, the influence of oblique-wave parameters on structural collapse is discussed, and the collapse mechanism of containerships under the action of oblique waves is obtained, which provides a new understanding of ship structure design.

Parameters affecting plug characteristics in dense phase pneumatic conveying of ellipsoidal particles

Even though particle shape tends to have a major influence on the bulk behaviour of a granular system, perfectly spherical particles are often used in numerical simulations. In this study, we examine the plug flow of ellipsoidal particles in dense phase horizontal pneumatic conveying within a rigid and cylindrical pipe with periodic boundaries in the axial direction. We use coupled Computational Fluid Dynamics (CFD) – Discrete Element Method (DEM) simulations to investigate the effect of particle shape on four plug characteristics: velocity, length, porosity, and particle exchange rate with the stationary bed. Both ellipsoidal and spherical particles are used, and the parameters varied are the particle size, aspect ratio, pressure gradient, particle–particle and particle–wall sliding and rolling friction coefficients, and coefficients of restitution. The steady state characteristics of plugs composed of spherical particles are distinctly different from those composed of ellipsoidal particles. Certain parameters, including the particle–wall rolling friction and restitution coefficients, have minimal impact on the steady state plug characteristics. The present study also suggests that introducing interparticle rolling friction for perfectly spherical particles can achieve the velocity and length appropriate for plugs composed of ellipsoidal particles, although differences in dynamics may persist. Overall, this comprehensive analysis offers valuable insights into plug flow behaviour with non-spherical particles, aiding in the efficient modelling and design of pneumatic conveying systems.

Microscopic insights into suction bucket installation in sand: Coupled coarse-grained CFD-DEM simulations

Suction bucket foundations are being used for a wide variety of offshore foundations. However, accurate modeling of its installation remains challenging due to the complexity of soil transportation, in which the soil is typically treated as a continuum and its discrete behavior is neglected. In this paper, the bucket foundation installation in the sand under different installation methods (i.e., jacked and suction-assisted installation) is investigated from a microscopic perspective (i.e., particle scale) based on the three-dimensional coupled computational fluid dynamics (CFD) and coarse-grained discrete element method (CGDEM). It is found that the CFD-CGDEM method can successfully simulate the bucket installation process. Suction-assisted installation results in a significant reduction in the inner skirt friction resistance and end resistance, while the outer skirt friction resistance shows only a minor decrease. During suction-assisted installation, soil loosening inside the bucket contributes more significantly to the soil plug formation compared to the inflow of external soil. Compared to jacked installation, the seepage induces a significant reduction in the effective stress of soil within the interior and below the bucket tip, while it increases the effective stress outside slightly under suction-assisted installation. The work provides an alternative research approach for the suction bucket installation.

Coupled Computational Fluid Dynamics and Computational Thermodynamics Simulations for Chemically Reacting Flows with Phase Transformations: A Fluoride Volatility Process Example

This study presents the development of a novel computational capability for chemically reacting flows with phase transformation that can be applied to complex multi-component systems. This is done by coupling Computational Fluid Dynamic (CFD) using OpenFOAM and Computational Thermodynamics (CT) using Thermochimica and the Joint Research Centre Molten Salt Database (JRCMSD). To illustrate this capability, the Fluorite Volatility Process (FVP) is modelled because it is the first step to clean up irradiated fuel salt in the Molten Salt Fast Reactor design and needs to be better understood. Local chemical equilibrium is assumed, which means that chemical kinetics is solely governed by mass transport. FVP recovers nuclear fuel UF4(liq) by injection of fluorine gas (F2), forming UF6(gas). The vaporization rate of UF4 is investigated on four different molten salt systems, using different dynamic viscosities and temperatures. The vaporization rate was shown to be clearly dependent on both thermochemical and thermophysical properties. Higher viscosities promoted larger bubbles, which delayed the chemical reaction. Results were compared to already available experimental data, showing good agreement. The applicability of coupling CFD with Thermochimica showed to be promising and expands interpretations on multiphysics systems and will be later applied to more complex scenarios.

Numerical Simulation of Spatial Atomic Layer Deposition on Moving Substrates with Microgrooves and Porous Structures

The need of ultrathin and highly conformal coatings on large-area microstructure substrates such as photovoltaic cells, flexible displays, and Li-ion battery (LIB) electrodes has driven the development of high-efficient ALD. Spatial ALD is a promising high-throughput technique capable of producing ultrathin films on large substrates, which can reach up to two orders of magnitude faster than temporal ALD. However, spatial ALD is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. Compared to the flat substrate, the diffusion process in the microstructures takes longer, limiting the substrate velocity and the deposition rate. In this work, spatial ALD on moving microgroove substrates and porous LIB electrodes are quantitatively studied through the multiscale modelling method by coupling computational fluid dynamics (CFD) with chemical kinetics. Dynamic mesh method is implemented to simulate the ALD reaction with the in-line movement of the substrate. Results show that the vortices always exist in the micro-gap with microgroove substrates. Besides, the top of the microstructure on the first contact with the precursor is the highest, and the surface coverage at the corner on the other side of the microstructure is the lowest. For porous LIB electrodes with large specific surface area, the film coating depth is limited by both the low precursor diffusion rate and the amount of precursor supply. Increasing the carrier gas flow rate increases the film coating depth by increasing the precursor supply over the same time period. Besides, the gas byproduct of ALD remaining at the electrode bottom can be more effectively removed. Quantitative process optimizations of substrate velocity and precursor concentration for different electrode structures are also carried out. It is found that the electrode gradient design with higher porosity on the top is beneficial for obtaining deeper coating depth and higher precursor utilization compared to the inverse gradient design. The present multiscale modeling work provides a comprehensive understanding and important guidance for the industrial application of the spatial ALD process on microstructure substrates.

Multi-scale analysis of seepage and erosion on collapse accumulation slope

This study focused on the slope surface of debris deposits during the Luwei Sea landslide. Through seepage erosion tests, nuclear magnetic resonance and the coupling of computational fluid dynamics with the discrete element method, the seepage erosion of four representative areas on the slope surface was systematically studied at the macroscopic, mesoscopic and microscopic levels. The results showed that the particle size distribution has a significant impact on the seepage erosion characteristics. When the ratio of soil to rock was higher, soil–rock mixture showed stronger resistance to infiltration and soil protection during seepage erosion. The applied osmotic pressure also affected seepage erosion. However, when the osmotic pressure exceeded a certain critical value, pore blockage became the main mechanism of seepage erosion. Furthermore, a vegetation-based soil stabilization method involving geotechnical reconstruction and material soil stabilization in unvegetated areas was proposed, thereby promoting vegetation growth and enhancing slope stability. Our findings provided effective measures and a strategic theoretical basis for the rehabilitation of mudslide accumulation sites.

Reconstruction of a Fluid Bed Device for Separating Granular Material from the Grinding Process of Rapid Antigen Tests

The article includes the study and reconstruction of a fluid bed device with the purpose of separating the granular material from the grinding process of rapid antigen tests. The following techniques were performed, with the purpose of characterisation of the ground particles: sieve analysis, X-ray fluorescence spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. The paper includes experimental testing of a simplified separation process with zeolite spheres and paper strips, supported by a numerical model. The flow conditions’ impact on the behaviour and interactions of particles of the considered problem were simulated using coupled computational fluid dynamics (CFD) and the discrete element method (DEM) approach. The separation process of zeolite spheres and paper strips was found to be efficient. The simulation results showed the appropriate behaviour of the particles during the process. We explained the results’ deviations, and we also presented the shortcomings and possible improvements. Further research is required to define the adequacy of the process, while using actual ground material of rapid antigen tests.

Advances in Coupling Computational Fluid Dynamics and Discrete Element Method in Geotechnical Problems

In some cases, the water content in granular soil increases to the extent that it becomes saturated, which noticeably alters its responses. For example, the pore water pressure within saturated granular soil would increase rapidly under sudden external loading, which is equivalent to undrained or constant volume conditions. This reduces the effective stress in soil dramatically and may result in catastrophic failure. There have been different numerical approaches to analyse such a failure mechanism of soil to provide a deeper understanding of soil behaviour at the microscopic level. One of the most common numerical tools for such analysis is the discrete element method (DEM) due to its advantage in obtaining microscopic properties (e.g., statistics on particle contacts and fabric), reproducibility and simple feedback control. However, most DEM studies ignore the fluid phase and merely consider the solid particles while the fluid pressure is indirectly calculated by mimicking undrained condition to a constant volume condition. Note that fluid’s influence does not limit to the change of pore water pressure. For example, the external loading would induce the movement of fluid, and the fluid-solid interaction could subsequently drag the solid particles to shift within the system. In addition, the state of soil could change from solid to suspension under an excess hydraulic gradient. Therefore, the study of the fluid-solid mixture is essential as it is a typical scenario in geotechnical practice, and the simulations of saturated sand should be conducted in numerical forms in which both the solid and fluid phases can be modelled.

CFD-DEM investigation of the effects of aperture size for a capsule-based dry powder inhaler

Capsule based dry powder inhalers (DPIs) often require piercing of the capsule before inhalation, and the characteristics of the apertures (punctured holes) affect air flow and the release of powders from the capsule. This work develops a numerical model based on the two-way coupling of computational fluid dynamics and discrete element method (CFD-DEM) to investigate the effect of aperture size on powder dispersion in the Aerolizer® device loaded with only carrier particles (lactose). Powders (carrier particles) in the size range 60–140 μm (d50: 90 μm and span: 0.66) were initialized in a capsule which had a circular aperture at each end. Boundary conditions corresponding to an air flow rate of 45 L/min were specified at each inlet to the mixing chamber (i.e., a total flow rate 90 L/min), and a capsule spin speed of ∼ 4050 rpm. The velocity magnitudes inside the capsule were considerably lower than those in the mixing chamber in the vicinity of the rotating capsule, with the exception of the capsules featuring 2.5 mm and 4 mm apertures. Larger apertures reduced the capsule emptying time and increased the particle evacuation velocity; the fluid drag force on the particles issuing from the capsule peaked for an aperture of 1.3 mm. Inside the capsule, particle–particle (PP) collisions were more frequent than particle–wall (PW) collisions due to high concentration of powder, but PP collisions had smaller (median) impact energy than PW collisions. Larger apertures resulted in fewer collisions in the capsule with higher PW and virtually unchanged PP collision energies. Outside the capsule (i.e., in the inhaler mixing chamber), PW collisions occurred more frequently than PP collisions with median collision energies typically two orders of magnitude higher than inside the capsule. Larger apertures resulted in more collisions with slightly reduced collision energy, but this effect plateaued for aperture sizes larger than 1.3 mm. Powder dispersion, expressed as the fine particle fraction (FPF) of the powder, was predicted using an empirical equation based on carrier PW collisions. Therefore, consistent with the model prediction of the effect of aperture sizes on the chamber collision frequency, FPF increased with aperture size but plateaued beyond 1.3 mm.

CFD–DEM modelling of the infiltration of non-spherical slurry particles in granular soils

The slurry filtration process at an excavation surface plays an important role in supporting pressure transmission, which is crucial to the stability of a tunnel face during slurry shield tunnelling. In this paper, a series of coupled computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulations were carried out to model the slurry filtration column test. Oblate spheroids of varying aspect ratios were adopted to represent slurry particles. A simplified pitching torque model was implemented to better simulate the motion of slurry particles. The pressure distribution, void fraction, permeability and orientations of the particles were analysed as the aspect ratio was systematically changed. The pressure distribution, void fraction and the permeability within a stratum are highly dependent on the aspect ratio of the particles. Particles with larger aspect ratios tend to effectively seal infiltration channels and transfer slurry pressure to effective pressure, thereby helping to maintain stability at the tunnel face. This research study explores how particle shape impacts the slurry infiltration procedure and the microstructure of the filter cake.

Transient Thermomechanical Stress Analysis of Hot Surface Ignition Device Using Sequentially Coupled Computational Fluid Dynamics–Finite Element Analysis Approach

Abstract Energy addition using a hot surface ignition device is required for reliable ignition of aircraft compression ignition engines running on fuel variations and at altitude conditions. Thus, durability of the hot surface ignition device is crucial for application in these engines. Thermomechanical stress is one of the key parameters that determine durability, which requires an accurate prediction of the transient temperature field based on well-defined boundary conditions representing the dynamic and complex fluid flow inside engines. To meet this requirement, the present study focuses on transient thermomechanical stress analysis using a sequentially coupled computational fluid dynamics (CFD)–finite element analysis (FEA) approach to understand transient thermomechanical responses of the hot surface ignition device. A three-dimensional transient reacting flow simulation was conducted first using converge software, the results of which were exported to map thermal and pressure boundary conditions onto a structural finite element mesh. Transient thermomechanical stress analysis was performed sequentially using abaqus software utilizing the mapped boundary conditions. The results such as transient temperature history, resultant thermomechanical stress, displacement, potential failure modes, etc., were critically reviewed, which can provide helpful information for further design improvement.

Simulation of the Frequency Response Analysis of Gas Diffusion in Zeolites by Means of Computational Fluid Dynamics

Frequency response (FR) analysis allows the characterization of gas diffusion occurring within a porous solid system. The shape of the pressure response curves obtained after a volume modulation in the reactor gives essential information about the gas adsorption and desorption properties of the porous material, e.g., zeolites, which is in contact with a certain gas environment, as well as information about the transport phenomena such as diffusion. In this work, a simulation model developed in COMSOL Multiphysics® is introduced to reproduce the experimental behavior of the tested solid/gas systems. This approach covers, for the first time, a coupling of computational fluid dynamics (CFD), porous media flow, and a customized mass adsorption/desorption function to simulate the behavior of real frequency response systems. The simulation results are compared to experimental data obtained from the interaction of propane in MFI zeolites as well as additional data from the literature to evaluate the model validity. Furthermore, a small variation study of the effect of simulation parameters such as the mass of the sample, bed porosity, or geometry is performed and analyzed. The essential advantage of this model with respect to other analytical approaches is to observe the spatial pressure and adsorption distribution (along with other local effects) of the gas within the porous material. Thus, local environments can be visualized, and non-idealities can, therefore, be detected in contrast to the general integral simulation approach.

Influence of the chemical kinetics on the prediction of turbulent non-premixed jet CH_4 flames

The present work focuses on the five different chemical mechanisms coupled with probability density function (PDF) model to represent the local extinction and re-ignition flame characteristics of the well-known Sandia Flames D–F. These five mechanisms span from the Foundational Fuel Chemistry Model (FFCM) mechanism involving 38 species to the Glarborg mechanism involving 150 species. The coupled computational fluid dynamics (CFD) and transported-PDF method are used for the turbulence modeling, and the reaction–diffusion manifolds (REDIMs) are used as an advanced technique for the simplification of chemical kinetics and to speed up the numerical computation. It is demonstrated that these chemical mechanisms have an ability to represent the degree of local extinction and re-ignition accurately. Furthermore, the sensitivity analysis shows that the degree of local extinction is very sensitive to only several key elementary reactions, and an analysis on the turbulence–chemistry interaction investigates the influence of these elementary reactions.