Journal articles on the topic 'Reactive premixted flow'
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1
Porumbel, Ionuţ, Andreea Cristina Petcu, Florin Gabriel Florean, and Constantin Eusebiu Hritcu. "Artificial Neural Networks for Modeling of Chemical Source Terms in CFD Simulations of Turbulent Reactive Flows." Applied Mechanics and Materials 555 (June 2014): 395–400. http://dx.doi.org/10.4028/www.scientific.net/amm.555.395.
Abstract:
The main goal of the work presented here was to develop, implement and test a highly efficient numerical algorithm for the evaluation of the chemical reaction source terms that appear in the Navier - Stokes equations when a turbulent, premixed, reactive flow is simulated using a finite rate chemistry combustion model. The approach was based on employing Artificial Neural Networks (ANN) that were designed, trained and incorporated into an existing LEM – LES numerical algorithm. Two numerical simulations of reacting flows have been carried out using several techniques for the estimation of the LES filtered reaction rate for the chemical species in laminar and turbulent, premixed, reactive flows, and the results were compared in terms of numerical accuracy and computational speed. It was concluded that the ANN approach provides a significant speedup of the numerical simulation while preserving acceptable accuracy.
2
KIM, SEUNG HYUN, and ROBERT W. BILGER. "Iso-surface mass flow density and its implications for turbulent mixing and combustion." Journal of Fluid Mechanics 590 (October 15, 2007): 381–409. http://dx.doi.org/10.1017/s0022112007008117.
Abstract:
A new result is derived for the mass flow rate per unit volume through a scalar iso-surface – called here the ‘iso-surface mass flow density’. The relationship of the surface mass flow density to the local entrainment rate per unit volume in scalar mixing and to the local reaction rate in turbulent premixed combustion is considered. In inhomogeneous flows, integration of the surface mass flow density across the layer in the direction of the mean scalar inhomogeneity yields the mean entrainment velocity in scalar mixing and the turbulent burning velocity in premixed combustion. For non-premixed turbulent reacting flow, this new result is shown to be consistent with the classical result of Bilger (Combust. Sci. Technol. vol. 13, 1976, p. 155) for fast one-step irreversible chemical reactions. Direct numerical simulation data for conserved scalar mixing, isothermal reaction front propagation and turbulent premixed flames are analysed. It is found that the entrainment velocity in the conserved scalar mixing case is sensitive to a threshold value. This suggests that the entrainment velocity is not a well-defined concept in temporally developing mixing layers and that scaling laws for the viscous superlayer warrant further investigation. In the isothermal reaction fronts problem, the characteristics of iso-surface propagation in a low Damköhler number regime are investigated. In premixed flames, the effects of non-stationarity on the turbulent burning velocity are addressed. The difference from the existing methods for determining turbulent burning velocity, and the implications of the present results for flames with multi-dimensional complex geometry are discussed. It is also shown that the surface mass flow density is related to the turbulent scalar flux in statistically stationary one-dimensional premixed flames. Variations of the local propagation characteristics due to departure from an unstretched laminar flame structure are shown to decrease the tendency to counter-gradient transport in turbulent premixed flames.
3
Martin, S. M., J. C. Kramlich, G. Kosa´ly, and J. J. Riley. "The Premixed Conditional Moment Closure Method Applied to Idealized Lean Premixed Gas Turbine Combustors." Journal of Engineering for Gas Turbines and Power 125, no. 4 (October 1, 2003): 895–900. http://dx.doi.org/10.1115/1.1587740.
Abstract:
This paper presents the premixed conditional moment closure (CMC) method as a new tool for modeling turbulent premixed combustion with detailed chemistry. By using conditional averages the CMC method can more accurately model the affects of the turbulent fluctuations of the temperature on the reaction rates. This provides an improved means of solving a major problem with traditional turbulent reacting flow models, namely how to close the reaction rate source term. Combined with a commercial CFD code this model provides insight into the emission formation pathways with reasonable runtimes. Results using the full GRI2.11 methane kinetic mechanism are compared to experimental data for a backward-facing step burning premixed methane. This model holds promise as a design tool for lean premixed gas turbine combustors.
4
Watanabe, Tomoaki, Yasuhiko Sakai, Kouji Nagata, and Osamu Terashima. "Turbulent Schmidt number and eddy diffusivity change with a chemical reaction." Journal of Fluid Mechanics 754 (July 30, 2014): 98–121. http://dx.doi.org/10.1017/jfm.2014.387.
Abstract:
AbstractWe provide empirical evidence that the eddy diffusivity$\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}D_{{t}\alpha }$and the turbulent Schmidt number${\mathit{Sc}}_{{t}\alpha }$of species$\alpha $($\alpha =\mathrm{A}, \mathrm{B}$or$\mathrm{R}$) change with a second-order chemical reaction ($\mathrm{A} + \mathrm{B} \rightarrow \mathrm{R}$). In this study, concentrations of the reactive species and axial velocity are simultaneously measured in a planar liquid jet. Reactant A is premixed into the jet flow and reactant B is premixed into the ambient flow. An optical fibre probe based on light absorption spectrometry is combined with I-type hot-film anemometry to simultaneously measure concentration and velocity in the reactive flow. The eddy diffusivities and the turbulent Schmidt numbers are estimated from the simultaneous measurement results. The results show that the chemical reaction increases${\mathit{Sc}}_{t\mathrm{A}}$;${\mathit{Sc}}_{t\mathrm{B}}$is negative in the region where the mean concentration of reactant B decreases in the downstream direction, and is positive in the non-reactive flow in the entire region on the jet centreline. It is also shown that${\mathit{Sc}}_{t\mathrm{R}}$is positive in the upstream region whereas it is negative in the downstream region. The production terms of axial turbulent mass fluxes of reactant B and product R can produce axial turbulent mass fluxes opposite to the axial gradients of the mean concentrations. The changes in the production terms due to the chemical reaction result in the negative turbulent Schmidt number of these species. These results imply that the gradient diffusion model using a global constant turbulent Schmidt number poorly predicts turbulent mass fluxes in reactive flows.
5
James, S., M. S. Anand, M. K. Razdan, and S. B. Pope. "In Situ Detailed Chemistry Calculations in Combustor Flow Analyses." Journal of Engineering for Gas Turbines and Power 123, no. 4 (March 1, 1999): 747–56. http://dx.doi.org/10.1115/1.1384878.
Abstract:
In the numerical simulation of turbulent reacting flows, the high computational cost of integrating the reaction equations precludes the inclusion of detailed chemistry schemes, therefore reduced reaction mechanisms have been the more popular route for describing combustion chemistry, albeit at the loss of generality. The in situ adaptive tabulation scheme (ISAT) has significantly alleviated this problem by facilitating the efficient integration of the reaction equations via a unique combination of direct integration and dynamic creation of a look-up table, thus allowing for the implementation of detailed chemistry schemes in turbulent reacting flow calculations. In the present paper, the probability density function (PDF) method for turbulent combustion modeling is combined with the ISAT in a combustor design system, and calculations of a piloted jet diffusion flame and a low-emissions premixed gas turbine combustor are performed. It is demonstrated that the results are in good agreement with experimental data and computations of practical turbulent reacting flows with detailed chemistry schemes are affordable.
6
Albayrak, Alp, Deniz A. Bezgin, and Wolfgang Polifke. "Response of a swirl flame to inertial waves." International Journal of Spray and Combustion Dynamics 10, no. 4 (December 20, 2017): 277–86. http://dx.doi.org/10.1177/1756827717747201.
Abstract:
Acoustic waves passing through a swirler generate inertial waves in rotating flow. In the present study, the response of a premixed flame to an inertial wave is scrutinized, with emphasis on the fundamental fluid-dynamic and flame-kinematic interaction mechanism. The analysis relies on linearized reactive flow equations, with a two-part solution strategy implemented in a finite element framework: Firstly, the steady state, low-Mach number, Navier–Stokes equations with Arrhenius type one-step reaction mechanism are solved by Newton’s method. The flame impulse response is then computed by transient solution of the analytically linearized reactive flow equations in the time domain, with mean flow quantities provided by the steady-state solution. The corresponding flame transfer function is retrieved by fitting a finite impulse response model. This approach is validated against experiments for a perfectly premixed, lean, methane-air Bunsen flame, and then applied to a laminar swirling flame. This academic case serves to investigate in a generic manner the impact of an inertial wave on the flame response. The structure of the inertial wave is characterized by modal decomposition. It is shown that axial and radial velocity fluctuations related to the eigenmodes of the inertial wave dominate the flame front modulations. The dispersive nature of the eigenmodes plays an important role in the flame response.
7
Yang, Wenkai, Ashraf N. Al Khateeb, and Dimitrios C. Kyritsis. "The Effect of Hydrogen Peroxide on NH3/O2 Counterflow Diffusion Flames." Energies 15, no. 6 (March 17, 2022): 2216. http://dx.doi.org/10.3390/en15062216.
Abstract:
The impact of adding H2O2 in the fuel stream on the structure of non-premixed opposed-flow NH3/O2 flames was investigated numerically using a verified computational tool and validated mechanism. The results illustrate the dual role of the added H2O2 within the fuel jet. A small amount of H2O2 within the NH3 stream acted as a fuel additive that enhanced the reaction rate via reducing the kinetic time scale. However, a novel flame structure appeared when the H2O2 mole fraction within the fuel stream increased to χH2O2 > 16%. Unlike the pure NH3/O2 flame, a premixed reaction zone was discerned on the fuel side, in which H2O2 reacts with NH3 and played the role of an oxidizer. Then, the remaining NH3 that survived premixed combustion continues reacting with O2 and forms a non-premixed flame. As a result of this structure, it was shown that the well-established conclusion of “near-equilibrium” non-premixed flame analysis in which the strain on the flame is determined by the momentum fluxes of the counter-flowing streams does not hold for the flames that were studied in this paper. It was also shown that when H2O2 acted as an oxidizer, it produced substantial amounts of HO2, which allowed for low-temperature formation of NO2 through the reaction of NO with HO2.
8
Sauer, Vinicius M., Fernando F. Fachini, and Derek Dunn-Rankin. "Non-premixed swirl-type tubular flames burning liquid fuels." Journal of Fluid Mechanics 846 (May 4, 2018): 210–39. http://dx.doi.org/10.1017/jfm.2018.248.
Abstract:
Tubular flames represent a canonical combustion configuration that can simplify reacting flow analysis and also be employed in practical power generation systems. In this paper, a theoretical model for non-premixed tubular flames, with delivery of liquid fuel through porous walls into a swirling flow field, is presented. Perturbation theory is used to analyse this new tubular flame configuration, which is the non-premixed equivalent to a premixed swirl-type tubular burner – following the original classification of premixed tubular systems into swirl and counterflow types. The incompressible viscous flow field is modelled with an axisymmetric similarity solution. Axial decay of the initial swirl velocity and surface mass transfer from the porous walls are considered through the superposition of laminar swirling flow on a Berman flow with uniform mass injection in a straight pipe. The flame structure is obtained assuming infinitely fast conversion of reactants into products and unity Lewis numbers, allowing the application of the Shvab–Zel’dovich coupling function approach.
9
Zhang, Yun Peng, Xiang Yang Wei, Xing Huang, and Bei Jing Zhong. "PAHs Formation Routes in the n-Heptane Laminar Flow Premixed Flame." Applied Mechanics and Materials 361-363 (August 2013): 1062–66. http://dx.doi.org/10.4028/www.scientific.net/amm.361-363.1062.
Abstract:
A detailed reaction mechanism is adopted to simulate n-heptane laminar premixed flame in this paper. The reaction mechanism comprises 108 components and 572 elementary reactions. The main reactants (O2,n-C7H16), reaction products (CO2,CO,H2,H2O), intermediate products (CH4, C2H4, C2H2, C3Hx) and the concentration distribution of PAHs in the flame are analyzed in the numerical method. The numerical results are in good agreement with the experimental results, which states that the mechanism can predict PAHs in the n-heptane flame. In this paper, the sensitivity and reaction flow analysis method is used to analyze the numerical results and the PAHs formation routes in n-heptane laminar flow premixed flame are obtained.
10
Lin, Ying, Xuesong Li, Martyn V. Twigg, and William F. Northrop. "A non-premixed reactive volatilization reactor for catalytic partial oxidation of low volatility fuels at a short contact time." Reaction Chemistry & Engineering 6, no. 4 (2021): 662–71. http://dx.doi.org/10.1039/d0re00460j.
Abstract:
This work presents a novel non-premixed opposed-flow reactive volatilization reactor that simultaneously vaporizes and partially oxidizes low volatility liquid hydrocarbons at a short contact time (<12 ms).
11
Gokulakrishnan, P., G. Gaines, J. Currano, M. S. Klassen, and R. J. Roby. "Experimental and Kinetic Modeling of Kerosene-Type Fuels at Gas Turbine Operating Conditions." Journal of Engineering for Gas Turbines and Power 129, no. 3 (May 31, 2006): 655–63. http://dx.doi.org/10.1115/1.2436575.
Abstract:
Experimental and kinetic modeling of kerosene-type fuels is reported in the present work with special emphasis on the low-temperature oxidation phenomenon relevant to gas turbine premixing conditions. Experiments were performed in an atmospheric pressure, tubular flow reactor to measure ignition delay time of kerosene (fuel–oil No. 1) in order to study the premature autoignition of liquid fuels at gas turbine premixing conditions. The experimental results indicate that the ignition delay time decreases exponentially with the equivalence ratio at fuel-lean conditions. However, for very high equivalence ratios (>2), the ignition delay time approaches an asymptotic value. Equivalence ratio fluctuations in the premixer can create conditions conducive for autoignition of fuel in the premixer, as the gas turbines generally operate under lean conditions during premixed prevaporized combustion. Ignition delay time measurements of stoichiometric fuel–oil No. 1∕air mixture at 1 atm were comparable with that of kerosene type Jet-A fuel available in the literature. A detailed kerosene mechanism with approximately 1400 reactions of 550 species is developed using a surrogate mixture of n-decane, n-propylcyclohexane, n-propylbenzene, and decene to represent the major chemical constituents of kerosene, namely n-alkanes, cyclo-alkanes, aromatics, and olefins, respectively. As the major portion of kerosene-type fuels consists of alkanes, which are relatively more reactive at low temperatures, a detailed kinetic mechanism is developed for n-decane oxidation including low temperature reaction kinetics. With the objective of achieving a more comprehensive kinetic model for n-decane, the mechanism is validated against target data for a wide range of experimental conditions available in the literature. The data include shock tube ignition delay time measurements, jet-stirred reactor reactivity profiles, and plug-flow reactor species time–history profiles. The kerosene model predictions agree fairly well with the ignition delay time measurements obtained in the present work as well as the data available in the literature for Jet A. The kerosene model was able to reproduce the low-temperature preignition reactivity profile of JP-8 obtained in a flow reactor at 12 atm. Also, the kerosene mechanism predicts the species reactivity profiles of Jet A-1 obtained in a jet-stirred reactor fairly well.
12
KURDYUMOV, VADIM N., and AMABLE LIÑÁN. "STRUCTURE OF A FLAME FRONT PROPAGATING AGAINST THE FLOW NEAR A COLD WALL." International Journal of Bifurcation and Chaos 12, no. 11 (November 2002): 2547–55. http://dx.doi.org/10.1142/s0218127402006023.
Abstract:
The flashback or propagation of premixed flames against the flow of a reacting mixture, along the low velocity region near a cold wall, is investigated numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the limiting reactant. Flame front propagation and flashback are only possible for values of the near wall velocity gradient below a critical value. The flame propagation becomes chaotic for small values of the Lewis number.
13
WATANABE, TOMOAKI, YASUHIKO SAKAI, KOUJI NAGATA, OSAMU TERASHIMA, HIROKI SUZUKI, TOSHIYUKI HAYASE, and YASUMASA ITO. "VISUALIZATION OF TURBULENT REACTIVE JET BY USING DIRECT NUMERICAL SIMULATION." International Journal of Modeling, Simulation, and Scientific Computing 04, supp01 (August 2013): 1341001. http://dx.doi.org/10.1142/s1793962313410018.
Abstract:
Direct numerical simulation (DNS) of turbulent planar jet with a second-order chemical reaction (A + B → R) is performed to investigate the processes of mixing and chemical reactions in spatially developing turbulent free shear flows. Reactant A is premixed into the jet flow, and reactant B is premixed into the ambient flow. DNS is performed at three different Damköhler numbers (Da = 0.1,1, and 10). Damköhler number is a ratio of a time scale of a flow to that of chemical reactions, and in this study, the large Da means a fast chemical reaction, and the small Da means a slow chemical reaction. The visualization of velocity field shows that the jet flow is developed by entraining the ambient fluid. The visualization of concentration of reactant A shows that concentration of reactant A for Da = 1 and 10 becomes very small in the downstream region because the chemical reaction consumes the reactants and reactant A is diffused with the jet development. By comparison of the profiles of chemical reaction rate and concentration of product R, it is found that product R for Da = 10 is produced by the chemical reaction at the interface between the jet and the ambient fluids and is diffused into the jet flow, whereas product R for Da = 0.1 is produced in the jet flow after reactants A and B are well mixed.
14
Rusak, Zvi, Jung J. Choi, Nicholas Bourquard, and Shixiao Wang. "Vortex breakdown in premixed reacting flows with swirl in a finite-length circular open pipe." Journal of Fluid Mechanics 793 (March 22, 2016): 749–76. http://dx.doi.org/10.1017/jfm.2016.140.
Abstract:
A global analysis of steady states of low Mach number inviscid premixed reacting swirling flows in a straight circular finite-length open pipe is developed. We focus on modelling the basic interaction between the swirl and heat release of the reaction. For analytic simplicity, a one-step first-order Arrhenious reaction kinetics is considered in the limit of high activation energy and infinite Peclet number. Assuming a complete reaction with chemical equilibrium upstream and downstream of the reaction zone, a nonlinear partial differential equation is derived for the solution of the flow stream function downstream of the reaction zone in terms of the specific total enthalpy, specific entropy and circulation functions prescribed at the inlet. Several types of solutions of the nonlinear ordinary differential equation for the columnar flow case describe the outlet states of the flow in a long pipe. These solutions are used to form the bifurcation diagram of steady reacting flows with swirl as the inlet swirl level is increased at a fixed heat release from the reaction. The approach is applied to two profiles of inlet flows, the solid-body rotation and the Lamb–Oseen vortex, both with constant profiles of the axial velocity, temperature and mixture reactant mass fraction. The computed results provide theoretical predictions of the critical inlet swirl levels for the appearance of vortex breakdown states and for the size of the breakdown zone as a function of the inlet flow swirl level, Mach number and heat release of the reaction. For the inlet solid-body rotation, flow is decelerated to breakdown as the inlet swirl is increased above the critical swirl level, and there is a delay in the appearance of breakdown with the increase of the heat release of the reaction. For the inlet Lamb–Oseen vortex at low values of heat release, the critical swirl for breakdown is decreased with the increase of heat release while, at high values of heat release, the appearance of breakdown is delayed to higher incoming flow swirl levels with the increase of heat release. The analysis sheds light on the global dynamics of low Mach number reacting flows with swirl and vortex breakdown and on the interaction between vortex breakdown and heat release that affects the shape of the reaction zone in the domain.
15
Zhou, Dezhi, Hongyuan Zhang, and Suo Yang. "A Robust Reacting Flow Solver with Computational Diagnostics Based on OpenFOAM and Cantera." Aerospace 9, no. 2 (February 14, 2022): 102. http://dx.doi.org/10.3390/aerospace9020102.
Abstract:
In this study, we developed a new reacting flow solver based on OpenFOAM (OF) and Cantera, with the capabilities of (i) dealing with detailed species transport and chemistry, (ii) integration using a well-balanced splitting scheme, and (iii) two advanced computational diagnostic methods. First of all, a flaw of the original OF chemistry model to deal with pressure-dependent reactions is fixed. This solver then couples Cantera with OF so that the robust chemistry reader, chemical reaction rate calculations, ordinary differential equations (ODEs) solver, and species transport properties handled by Cantera can be accessed by OF. In this way, two transport models (mixture-averaged and constant Lewis number models) are implemented in the coupled solver. Finally, both the Strang splitting scheme and a well-balanced splitting scheme are implemented in this solver. The newly added features are then assessed and validated via a series of auto-ignition tests, a perfectly stirred reactor, a 1D unstretched laminar premixed flame, a 2D counter-flow laminar diffusion flame, and a 3D turbulent partially premixed flame (Sandia Flame D). It is shown that the well-balanced property is crucial for splitting schemes to accurately capture the ignition and extinction events. To facilitate the understanding on combustion modes and complex chemistry in large scale simulations, two computational diagnostic methods (conservative chemical explosive mode analysis, CCEMA, and global pathway analysis, GPA) are subsequently implemented in the current framework and used to study Sandia Flame D for the first time. It is shown that these two diagnostic methods can extract the flame structure, combustion modes, and controlling global reaction pathways from the simulation data.
16
Chakraborty, Nilanjan, and Cesar Dopazo. "Timescales Associated with the Evolution of Reactive Scalar Gradient in Premixed Turbulent Combustion: A Direct Numerical Simulation Analysis." Fire 7, no. 3 (February 29, 2024): 73. http://dx.doi.org/10.3390/fire7030073.
Abstract:
The fractional change in the reaction progress variable gradient depends on the flow normal straining within the flame and also upon the corresponding normal gradients of the reaction rate and its molecular diffusion transport. The statistical behaviours of the normal strain rate and the contributions arising from the normal gradients of the reaction rate and molecular diffusion rate within the flame were analysed by means of a Direct Numerical Simulation (DNS) database of statistically planar turbulent premixed flames ranging from the wrinkled/corrugated flamelets regime to the thin reaction zones regime. The interaction of flame-normal straining with the flame-normal gradient of molecular diffusion rate was found to govern the reactive scalar gradient transport in the preheat zone, where comparable timescales for turbulent straining and molecular diffusion are obtained for small values of Karlovitz numbers. However, the molecular diffusion timescale turns out to be smaller than the turbulent straining timescale for high values of Karlovitz numbers. By contrast, the reaction and hot product zones of the flame remain mostly unaffected by turbulence, and the reactive scalar gradient transport in this zone is determined by the interaction between the flame-normal gradients of molecular diffusion and chemical reaction rates.
17
Alshaalan, T., and C. J. Rutland. "Wall heat flux in turbulent premixed reacting flow." Combustion Science and Technology 174, no. 1 (January 2002): 135–65. http://dx.doi.org/10.1080/713712913.
18
LIVESCU, D., F. A. JABERI, and C. K. MADNIA. "The effects of heat release on the energy exchange in reacting turbulent shear flow." Journal of Fluid Mechanics 450 (January 9, 2002): 35–66. http://dx.doi.org/10.1017/s0022112001006164.
Abstract:
The energy exchange between the kinetic and internal energies in non-premixed reacting compressible homogeneous turbulent shear flow is studied via data generated by direct numerical simulations (DNS). The chemical reaction is modelled by a one- step exothermic irreversible reaction with Arrhenius-type reaction rate. The results show that the heat release has a damping effect on the turbulent kinetic energy for the cases with variable transport properties. The growth rate of the turbulent kinetic energy is primarily in uenced by the reaction through temperature-induced changes in the solenoidal dissipation and modifications in the explicit dilatational terms (pressure–dilatation and dilatational dissipation). The production term in the scaled kinetic energy equation, which is proportional to the Reynolds shear stress anisotropy, is less affected by the heat release. However, the dilatational part of the production term increases during the time when the reaction is important. Additionally, the pressure–dilatation correlation, unlike the non-reacting case, transfers energy in the reacting cases, on the average, from the internal to the kinetic energy. Consequently, the dilatational part of the kinetic energy is enhanced by the reaction. On the contrary, the solenoidal part of the kinetic energy decreases in the reacting cases mainly due to an enhanced viscous dissipation. Similarly to the non-reacting case, it is found that the direct coupling between the solenoidal and dilatational parts of the kinetic energy is small. The structure of the flow with regard to the normal Reynolds stresses is affected by the heat of reaction. Compared to the non-reacting case, the kinetic energy in the direction of the mean velocity decreases during the time when the reaction is important, while it increases in the direction of the shear. This increase is due to the amplification of the dilatational kinetic energy in the x2-direction by the reaction. Moreover, the dilatational effects occur primarily in the direction of the shear. These effects are amplified if the heat release is increased or the reaction occurs at later times. The non-reacting models tested for the explicit dilatational terms are not supported by the DNS data for the reacting cases, although it appears that some of the assumptions employed in these models hold also in the presence of heat of reaction.
19
Liou, Tong-Miin, Po-Wen Hwang, Yi-Chen Li, and Chia-Yen Chan. "Flame Stability Analysis of Turbulent Non-Premixed Reacting Flow in a Simulated Solid-Fuel Ramjet Combustor." Journal of Mechanics 18, no. 1 (March 2002): 43–51. http://dx.doi.org/10.1017/s172771910000201x.
Abstract:
ABSTRACTTo investigate the flame stability in a solid-fuel ramjet combustor, time-accurate calculations using a compressible flow solver with a modified Godunov flux-splitting scheme have been performed on high Reynolds number turbulent non-premixed reacting flows over a backward-facing step with mass bleed on one wall. The combustion process considered was a one-step, irreversible, and finite rate chemical reaction. The numerical results for reacting flows show that the two-dimensional (2-D) simulations can provide reasonable predictions on the dimensionless particle number decay rate and residence time in the flame holding recirculation zone, evolutions of both axial and transverse mean velocity profiles, and critical characteristic exhaust velocity separating the sustained combustion from the non-sustained combustion. In addition to the validation of 2-D reacting flow calculations, two- and three-dimensionally computed mean-velocity profiles are compared with existing experimental data for isothermal flows to check the suitability of 2-D simulations on capturing the large-scale mean flows.
20
Yang, Gelan, Huixia Jin, and Na Bai. "A Numerical Study on Premixed Bluff Body Flame of Different Bluff Apex Angle." Mathematical Problems in Engineering 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/272567.
Abstract:
In order to investigate effects of apex angle (α) on chemically reacting turbulent flow and thermal fields in a channel with a bluff body V-gutter flame holder, a numerical study has been carried out in this paper. With a basic geometry used in a previous experimental study, the apex angle was varied from 45° to 150°. Eddy dissipation concept (EDC) combustion model was used for air and propane premixed flame. LES-Smagorinsky model was selected for turbulence. The gird-dependent learning and numerical model verification were done. Both nonreactive and reactive conditions were analyzed and compared. The results show that asαincreases, recirculation zone becomes bigger, and Strouhal number increases a little in nonreactive cases while decreases a little in reactive cases, and the increase ofαmakes the flame shape wider, which will increase the chamber volume heat release ratio and enhance the flame stability.
21
Chen, W. H. "Partially Premixed Flame Structure and Stability of Twin Droplets in Flows." Journal of Heat Transfer 122, no. 4 (June 5, 2000): 730–40. http://dx.doi.org/10.1115/1.1318212.
Abstract:
The flame structure and stability, as well as the vaporization rates of twin droplets exposed to a high-temperature, partially premixed flow are investigated in the present study. Two important parameters of the Reynolds number and ambient equivalence ratio are taken into consideration to account for the influence of fuel vapor in the upstream far field on those of burning mechanisms around the twin droplets. When increasing the ambient equivalence ratio, the chemical reactivity in the upstream can be classified into three types; weakly, moderately, and obviously reactive flows, according to the distribution of the vaporization rate of the leading droplet versus the Reynolds number. In particular, if the flow is moderately reactive, say, ϕ=0.2, a double-peak profile is observed in the vaporization rate of the leading droplet, and it clearly depicts that by increasing the Reynolds number the vaporization is sequentially dominated by the envelope flame, reactive flow, and convective flow. With regard to the trailing droplet, because of the multiple effects stemming from the leading droplet, the impact of the ambient equivalence ratio on the vaporization rate distribution is similar, except for in the purely oxidizing environment in which the twin droplets behave as a single droplet. As a whole, the evaluated results illustrate that the partially premixed flow is conducive to promoting the vaporization and aides the flame stability in a twin-droplet system, while some burning characteristics in a counterflow system can also be obtained in front of the leading droplet. [S0022-1481(00)01504-8]
22
Hossain, Md Amzad, Md Nawshad Arslan Islam, Martin De La Torre, Arturo Acosta Zamora, and Ahsan Choudhuri. "Fundamental Study of Premixed Methane Air Combustion in Extreme Turbulent Conditions Using PIV and C-X CH PLIF." Aerospace 10, no. 7 (July 8, 2023): 620. http://dx.doi.org/10.3390/aerospace10070620.
Abstract:
This paper presents the flow and flame characteristics of a highly turbulent reactive flow over a backward-facing step inside a windowed combustor. Flow and combustion experiments were performed at Re = 15,000 and Re = 30,000 using high-resolution 10 kHz PIV and 10 kHz PLIF diagnostic techniques. Grid turbulators (Grid) with two different hole diameters (HD of 1.5 mm and 3 mm) and blockage ratios (BR of 46%, 48%, 62%, and 63%) were considered for the turbulence study. Grids introduced different turbulent length scales (LT) in the flow, causing the small eddies and turbulence intensity to increase downstream. The backward-facing step increased the turbulence level in the recirculation zone. This helped to anchor the flame in that zone. The small HD grids (Grids 1 and 3) produced continuous fluid structures (small-scale), whereas the larger HD grids (Grids 2 and 4) produced large-scale fluid structures. Consequently, the velocity fluctuation was lower (~25.6 m/s) under small HD grids and higher (~27.7 m/s) under large HD grids. The flame study was performed at Φ = 0.8, 1.0, and 1.2 using C-X CH PLIF. An Adaptive MATLAB-based flame imaging scheme has been developed for turbulent reacting flows. Grids 1 and 3 induced more wrinkles in the flame due to higher thermal instabilities, pressure fluctuation, and diffusion under those grids. The flamelet breakdown and burnout events were higher under Grids 2 and 4 due to higher thermal diffusivity and a slower diffusion rate. It was observed that the flame wrinkling and flame stretching are higher at Re = 30,000 compared to Re = 15,000. The Borghi–Peters diagram showed that the flames were within the thin reaction zone except for Grid 1 at Re = 15,000, where flames fell in the corrugated zone. It was observed from PIV and PLIF analyses that Re and LT mostly controlled the flame and flow characteristics.
23
Dulin, Vladimir, Leonid Chikishev, Dmitriy Markovich, and Kemal Hanjalic. "Modification of Swirling Jet Flow by Premixed Combustion." Siberian Journal of Physics 7, no. 4 (December 1, 2012): 68–78. http://dx.doi.org/10.54362/1818-7919-2012-7-4-68-78.
Abstract:
Effect of combustion of propane-air mixture in a weakly and strongly swirling jet was studied. The rate of swirl was classified in terms of the absence / presence of a stable recirculation zone in the non-reacting jet flow. Sequences of the instantaneous velocity fields were measured in lean and rich flames at atmospheric pressure, and also in the non-reacting flow, by using a high-repetition stereoscopic particle image velocimetry system. Spatial distributions of the time-averaged velocity and Reynolds stresses, calculated from the sequences, revealed that combustion of rich mixture dramatically affected structure of flow and type of vortex breakdown
24
Dang, Nannan, Jiazhong Zhang, and Yoshihiro Deguchi. "Numerical Study on the Route of Flame-Induced Thermoacoustic Instability in a Rijke Burner." Applied Sciences 11, no. 4 (February 10, 2021): 1590. http://dx.doi.org/10.3390/app11041590.
Abstract:
The self-excited thermoacoustic instability in a two-dimensional Rijke-type burner with a center-stabilized premixed methane–air flame is numerically studied. The simulation considers the reacting flow, flame dynamics, and radiation model to investigate the important physical processes. A finite volume-based approach is used to simulate reacting flows under both laminar and turbulent flow conditions. Chemical reaction modeling is conducted via the finite-rate/eddy dissipation model with one-step reaction mechanisms, and the radiation heat flux and turbulent flow characteristics are determined by using the P-1 model and the standard k-ε model, respectively. The steady-state reacting flow is first simulated for model verification. Then, the dynamic pressure, velocity, and reaction heat evolutions are determined to show the onset and growth rate of self-excited instability in the burner. Using the fast Fourier transform (FFT) method, the frequency of the limit cycle oscillation is obtained, which agrees well with the theoretical prediction. The dynamic pressure and velocity along the tube axis provide the acoustic oscillation mode and amplitude, also agreeing well with the prediction. Finally, the unsteady flow field at different times in a limit cycle shows that flame-induced vortices occur inside the combustor, and the temperature distribution indicates that the back-and-forth velocity changes in the tube vary the distance between the flame and honeycomb in turn, forming a forward feedback loop in the tube. The results reveal the route of flame-induced thermoacoustic instability in the Rijke-type burner and indicate periodical vortex formation and breakdown in the Rijke burner, which should be considered turbulent flow under thermoacoustic instability.
25
Martinez-Sanchis, Daniel, Andrej Sternin, Oskar Haidn, and Martin Tajmar. "Combustion Regimes in Turbulent Non-Premixed Flames for Space Propulsion." Aerospace 10, no. 8 (July 28, 2023): 671. http://dx.doi.org/10.3390/aerospace10080671.
Abstract:
Direct numerical simulations of non-premixed fuel-rich methane–oxygen flames at 20 bar are conducted to investigate the turbulent mixing burning of gaseous propellants in rocket engines. The reacting flow is simulated by using an EBI-DNS solver within an OpenFOAM frame. The transport of species is resolved with finite-rate chemistry by using a complex skeletal mechanism that entails 21 species. Two different flames at low and high Reynolds numbers are considered to study the sensitivity of the flame dynamics to turbulence. Regime markers are used to measure the probability of the flow to burn in premixed and non-premixed conditions at different regions. The local heat release statistics are studied in order to understand the drivers in the development of the turbulent diffusion flame. Despite the eminent non-premixed configuration, a significant amount of combustion takes place in premixed conditions. Premixed combustion is viable in both lean and fuel-rich regions, relatively far from the stoichiometric line. It has been found that a growing turbulent kinetic energy is detrimental to combustion in fuel-rich premixed conditions. This is motivated by the disruption of the local premixed flame front, which promotes fuel transport into the diffusion flame. In addition, at downstream positions, higher turbulence enables the advection of methane into the lean core of the flame, enhancing the burning rates in these regions. Therefore, the primary effect of turbulence is to increase the fraction of propellants burnt in oxygen-rich and near-stoichiometric conditions. Consequently, the mixture fraction of the products shifts towards lean conditions, influencing combustion completion at downstream positions.
26
Giacomazzi, Eugenio, Donato Cecere, Matteo Cimini, and Simone Carpenella. "Direct Numerical Simulation of a Reacting Turbulent Hydrogen/Ammonia/Nitrogen Jet in an Air Crossflow at 5 Bar." Energies 16, no. 23 (November 22, 2023): 7704. http://dx.doi.org/10.3390/en16237704.
Abstract:
The article aims to analyze the fluid dynamics and combustion characteristics of a non-premixed flame burning a fuel mixture derived from ammonia partial decomposition injected in an air crossflow. Nominal pressure (5 bar) and inlet air temperature (750 K) conditions are typical of micro-gas turbines. The effects of strain on the maximum flame temperature and NO generation in laminar non-premixed counter-flow flames are initially explored. Then, the whole three-dimensional fluid dynamic problem is investigated by setting up a numerical experiment: it consists of a Direct Numerical Simulation, based on accurate transport, chemical, and numerical models. The flow topology of the specific reacting jet in crossflow configuration is described in terms of its main turbulent structures, like shear layers, ring, and horse-shoe vortices, as well as of its leeward recirculation region anchoring the flame. The reacting region is characterized by providing instantaneous spatial distributions of temperature, heat release, and some transported chemical species, including NO, and calculating the Flame Index to identify non-premixed and premixed combustion local conditions. The latter is quantified by looking at the distribution of the volume fraction associated with a certain Flame Index versus the Flame Index and at the distribution of the average values of both the Heat Release Rate and NO versus the Flame Index and the mixture fraction.
27
Dourado, W. M. C., P. Bruel, and J. L. F. Azevedo. "A STEADY PSEUDO-COMPRESSIBILITY APPROACH BASED ON UNSTRUCTURED HYBRID FINITE VOLUME TECHNIQUES APPLIED TO TURBULENT PREMIXED FLAME PROPAGATION." Revista de Engenharia Térmica 2, no. 2 (December 31, 2003): 41. http://dx.doi.org/10.5380/reterm.v2i2.3475.
Abstract:
A pseudo-compressibility method for zero Mach number turbulent reactive
flows with heat release is combined with an unstructured finite volume
hybrid grid scheme. The spatial discretization is based on an overlapped cell
vertex approach. An infinite freely planar flame propagating into a turbulent
medium of premixed reactants is considered as a test case. The recourse to a
flamelet combustion modeling for which the reaction rate is quenched in a
continuous way ensures the uniqueness of the turbulent flame propagation
velocity. To integrate the final form of discretized governing equations, a
three-stage hybrid time-stepping scheme is used and artificial dissipation
terms are added to stabilize the convergence path towards the final steady
solution. The results obtained with such a numerical procedure prove to be
in good agreement with those reported in the literature on the very same
flow geometry. Indeed, the flame structure as well as its propagation
velocity are accurately predicted thus confirming the validity of the
approach followed and demonstrating that such a numerical procedure will
be a valuable tool to deal with complex reactive flow geometries.
28
Chakraborty, Nilanjan. "Influence of Thermal Expansion on Fluid Dynamics of Turbulent Premixed Combustion and Its Modelling Implications." Flow, Turbulence and Combustion 106, no. 3 (March 2021): 753–848. http://dx.doi.org/10.1007/s10494-020-00237-8.
Abstract:
AbstractThe purpose of this paper is to demonstrate the effects of thermal expansion, as a result of heat release arising from exothermic chemical reactions, on the underlying turbulent fluid dynamics and its modelling in the case of turbulent premixed combustion. The thermal expansion due to heat release gives rise to predominantly positive values of dilatation rate within turbulent premixed flames, which has been shown to have significant implications on the flow topology distributions, and turbulent kinetic energy and enstrophy evolutions. It has been demonstrated that the magnitude of predominantly positive dilatation rate provides the measure of the strength of thermal expansion. The influence of thermal expansion on fluid turbulence has been shown to strengthen with decreasing values of Karlovitz number and characteristic Lewis number, and with increasing density ratio between unburned and burned gases. This is reflected in the weakening of the contributions of flow topologies, which are obtained only for positive values of dilatation rate, with increasing Karlovitz number. The thermal expansion within premixed turbulent flames not only induces mostly positive dilatation rate but also induces a flame-induced pressure gradient due to flame normal acceleration. The correlation between the pressure and dilatation fluctuations, and the vector product between density and pressure gradients significantly affect the evolutions of turbulent kinetic energy and enstrophy within turbulent premixed flames through pressure-dilatation and baroclinic torque terms, respectively. The relative contributions of pressure-dilatation and baroclinic torque in comparison to the magnitudes of the other terms in the turbulent kinetic energy and enstrophy transport equations, respectively strengthen with decreasing values of Karlovitz and characteristic Lewis numbers. This leads to significant augmentations of turbulent kinetic energy and enstrophy within the flame brush for small values of Karlovitz and characteristic Lewis numbers, but both turbulent kinetic energy and enstrophy decay from the unburned to the burned gas side of the flame brush for large values of Karlovitz and characteristic Lewis numbers. The heat release within premixed flames also induces significant anisotropy of sub-grid stresses and affects their alignments with resolved strain rates. This anisotropy plays a key role in the modelling of sub-grid stresses and the explicit closure of the isotropic part of the sub-grid stress has been demonstrated to improve the performance of sub-grid stress and turbulent kinetic energy closures. Moreover, the usual dynamic modelling techniques, which are used for non-reacting turbulent flows, have been shown to not be suitable for turbulent premixed flames. Furthermore, the velocity increase across the flame due to flame normal acceleration may induce counter-gradient transport for turbulent kinetic energy, reactive scalars, scalar gradients and scalar variances in premixed turbulent flames under some conditions. The propensity of counter-gradient transport increases with decreasing values of root-mean-square turbulent velocity and characteristic Lewis number. It has been found that vorticity aligns predominantly with the intermediate principal strain rate eigendirection but the relative extents of alignment of vorticity with the most extensive and the most compressive principal strain rate eigendirections change in response to the strength of thermal expansion. It has been found that dilatation rate almost equates to the most extensive strain rate for small sub-unity Lewis numbers and for the combination of large Damköhler and small Karlovitz numbers, and under these conditions vorticity shows no alignment with the most extensive principal strain rate eigendirection but an increased collinear alignment with the most compressive principal strain rate eigendirection is obtained. By contrast, for the combination of high Karlovitz number and low Damköhler number in the flames with Lewis number close to unity, vorticity shows an increased collinear alignment with the most extensive principal direction in the reaction zone where the effects of heat release are strong. The strengthening of flame normal acceleration in comparison to turbulent straining with increasing values of density ratio, Damköhler number and decreasing Lewis number makes the reactive scalar gradient align preferentially with the most extensive principal strain rate eigendirection, which is in contrast to preferential collinear alignment of the passive scalar gradient with the most compressive principal strain rate eigendirection. For high Karlovitz number, the reactive scalar gradient alignment starts to resemble the behaviour observed in the case of passive scalar mixing. The influence of thermal expansion on the alignment characteristics of vorticity and reactive scalar gradient with local principal strain rate eigendirections dictates the statistics of vortex-stretching term in the enstrophy transport equation and normal strain rate contributions in the scalar dissipation rate and flame surface density transport equations, respectively. Based on the aforementioned fundamental physical information regarding the thermal expansion effects on fluid turbulence in premixed combustion, it has been argued that turbulence and combustion modelling are closely interlinked in turbulent premixed combustion. Therefore, it might be necessary to alter and adapt both turbulence and combustion modelling strategies while moving from one combustion regime to the other.
29
Wahls, Benjamin H., and Srinath V. Ekkad. "A new technique using background oriented schlieren for temperature reconstruction of an axisymmetric open reactive flow." Measurement Science and Technology 33, no. 5 (February 21, 2022): 055202. http://dx.doi.org/10.1088/1361-6501/ac51a5.
Abstract:
Abstract A new technique, called 3D ray tracing, for refractive index field reconstruction of axisymmetric flows from displacement fields measured from background oriented schlieren (BOS) experiments is developed and applied to a lean premixed methane/air reactive flow at Reynolds number of 4000 on a 12 mm diameter circular burner. The temperature distribution is then calculated using a species independent direct relationship between refractive index, temperature, and ambient conditions. The error introduced by the approximation to reach this relationship is quantified using simulated flow fields and is found to be 8% within the inner unburnt region of the flow field, decreasing to 2% through the reaction zone, and then quickly reducing to 0% outside the flow field. The effect of random noise and reconstruction resolution on the accuracy of the method is assessed via application to synthetically generated data sets that mimic the characteristics of a heated air jet expelled into ambient. The novel 3D ray tracing allows for accurate temperature reconstructions of open axisymmetric reactive flows where 2D displacement fields are measured, which is shown to be a shortcoming of current direct methods in literature. Additionally, this is done without the need for any prior knowledge of flow field parameters; only ambient conditions to the system must be known. The simple experimental setup and low computational cost make this approach with BOS a good option for application into existing experimental combustion systems with minimal effort.
30
Li, Guang-Xin, Ming-Bo Sun, Yi-Xin Yang, Tai-Yu Wang, and Yuan Liu. "Spatial structural characteristics of a combustion flow field in an ethylene-fueled supersonic combustor with a rear-wall-expansion cavity." Modern Physics Letters B 34, no. 18 (June 23, 2020): 2050208. http://dx.doi.org/10.1142/s0217984920502085.
Abstract:
A hybrid large eddy simulation (LES)/assumed subgrid probability density function (PDF) closure model was employed to investigate the structural characteristics of the combustion flow field in an ethylene-fueled supersonic combustor with a rear-wall-expansion cavity. The wall pressure distribution from numerical simulation was compared with experimental data, and the numerical results are in good agreement with the experimental data. The spatial distribution characteristics of combustion heat release in the flow field are obtained from the simulation results. The reaction heat release zone is mainly distributed in the cavity. The cavity shear layer forms a concentrated reaction zone that produces a large amount of chemical heat release, thus further maintaining local stable combustion and forming a flame base. The front part of the cavity shear layer has the highest temperature in the whole flow field. There is still excess fuel reaching the cavity rear wall and producing a certain intensity of reaction. In addition, a dispersed small flame intermittently forms in the downstream near-wall region. The premixed combustion mode dominates the cavity recirculation zone, while the combustion in the downstream region evidently shows a non-premixed mode.
31
Bioche, K., L. Vervisch, and G. Ribert. "Premixed flame–wall interaction in a narrow channel: impact of wall thermal conductivity and heat losses." Journal of Fluid Mechanics 856 (September 28, 2018): 5–35. http://dx.doi.org/10.1017/jfm.2018.681.
Abstract:
The flow physics controlling the stabilisation of a methane/air laminar premixed flame in a narrow channel (internal width $\ell _{i}=5~\text{mm}$) is revisited from numerical simulations. Combustion is described with complex chemistry and transport properties, along with a coupled simulation of heat transfer at and within the wall. To conduct a thorough analysis of the flame–wall interaction, the steady flame is obtained after applying a procedure to find the inlet mass flow rate that exactly matches the flame mass burning rate. The response of the premixed flame shape to various operating conditions is then analysed in terms of flame propagation velocity and flow topology in the vicinity of the reactive front. We focus on the interrelations between the flame speed, the configuration taken by the flame surface, the flow deviation induced by the heat released and the fluxes at the wall. Compared to an adiabatic flame, the flame speed increases with edge-flame quenching at an isothermal cold wall in the absence of a boundary layer, decreases with a boundary layer, to increase again with heat-transfer coupling within the wall. A regime diagram is proposed to delineate between flame shapes in order to build a classification versus heat-transfer properties. Under a small level of convective heat transfer with the ambient air surrounding the channel, the larger the thermal conductivity in the solid, the faster the reaction zone propagates in the vicinity of the wall, leaving the centreline reaction zone behind. The premixed flame front is then concave towards the fresh gases on the axis of symmetry (so-called tulip flame) with a flame speed higher than in the adiabatic case. Increasing the heat loss at the wall through convection with ambient air, the flame shape becomes convex (mushroom flame) and the flame speed decreases below its adiabatic level. Scaling laws are provided for the flame speed under these various regimes. Mesh resolution was calibrated, with and without heat loss, from simulations of one-dimensional detailed chemistry flames, leading to mesh resolution of $12.5~\unicode[STIX]{x03BC}\text{m}$ for detailed chemistry and $25.0~\unicode[STIX]{x03BC}\text{m}$ with a skeleton mechanism. The quality of the resolution was also assessed from multi-physics budgets derived from first principles, involving upstream-flame heat retrocession by the wall leading to flow acceleration, budgets bringing physical insights into flame/wall interaction. Additional overall mesh convergence tests of the multi-physics solution would have been desirable, but were not conducted due to the high computing cost of these fully compressible simulations, hence also solving for the acoustic field with low convective velocities.
32
Jiang, Hanyu, and Yue Huang. "Numerical investigation of non-premixed H2-Air rotating detonation combustor with different equivalence ratios." Journal of Physics: Conference Series 2235, no. 1 (May 1, 2022): 012011. http://dx.doi.org/10.1088/1742-6596/2235/1/012011.
Abstract:
Abstract The initiation and propagation of rotating detonation waves (RDWs) are key techniques for the engineering application of rotating detonation engine (RDE). In this paper, the Naiver-Stokes equation of the three-dimensional unsteady reaction flow has been solved using one step hydrogen/air reaction mechanism to investigate the formation and propagation processes of RDWs under the non-premixed condition with different inlet equivalence ratios. The numerical results show that compared with RDWs generated by premixed propellants, less stable propagation processes and lower detonation fronts can be observed in RDWs generated under the non-premixed condition. It can be also concluded that the equivalence ratio has a great effect on the formation and propagation of RDWs. The formation time of stable RDWs increases when the ER changes from 1.0 to 1.3. However, under the conditions of the two ERs, similar re-initiation phenomena is observed in the evolution process of RDWs and a three-wave mode has been established.
33
Wacks, Daniel, Ilias Konstantinou, and Nilanjan Chakraborty. "Effects of Lewis number on the statistics of the invariants of the velocity gradient tensor and local flow topologies in turbulent premixed flames." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2212 (April 2018): 20170706. http://dx.doi.org/10.1098/rspa.2017.0706.
Abstract:
The behaviours of the three invariants of the velocity gradient tensor and the resultant local flow topologies in turbulent premixed flames have been analysed using three-dimensional direct numerical simulation data for different values of the characteristic Lewis number ranging from 0.34 to 1.2. The results have been analysed to reveal the statistical behaviours of the invariants and the flow topologies conditional upon the reaction progress variable. The behaviours of the invariants have been explained in terms of the relative strengths of the thermal and mass diffusions, embodied by the influence of the Lewis number on turbulent premixed combustion. Similarly, the behaviours of the flow topologies have been explained in terms not only of the Lewis number but also of the likelihood of the occurrence of individual flow topologies in the different flame regions. Furthermore, the sensitivity of the joint probability density function of the second and third invariants and the joint probability density functions of the mean and Gaussian curvatures to the variation in Lewis number have similarly been examined. Finally, the dependences of the scalar--turbulence interaction term on augmented heat release and of the vortex-stretching term on flame-induced turbulence have been explained in terms of the Lewis number, flow topology and reaction progress variable.
34
Muppala, Siva, and Vendra C. Madhav Rao. "Numerical Implementation and validation of turbulent premixed combustion model for lean mixtures." MATEC Web of Conferences 209 (2018): 00004. http://dx.doi.org/10.1051/matecconf/201820900004.
Abstract:
The present paper discusses the numerical investigation of turbulent premixed flames under lean conditions. Lean premixed combustion, a low NOx emission technique but are prone to instabilities, extinction and blow out. Such flames are influenced by preferential diffusion due to different mass diffusivities of reactants and difference between heat and mass diffusivities in the reaction zone. In this numerical study, we estimate non-reacting flow characteristics with implementation of an Algebraic Flame Surface Wrinkling Model (AFSW) in the open source CFD code OpenFOAM. In these flows, the mean velocity fields and recirculation zones were captured reasonably well by the RANS standard k-epsilon turbulence model. The simulated turbulent velocity is in good agreement with experiments in the shear-generated turbulence layer. The reacting flow study was done at three equivalence ratios of 0.43, 0.5 and 0.56 to gauge the ability of numerical model to predict combustion quantities. At equivalence ratios 0.5 and 0.56 the simulations showed numerical oscillations and non-convergence of the turbulent quantities. This leads to a detailed parametric variation study where, the pre-constant of AFSW model is varied with values 0.3, 0.35 and 0.4. However the study revealed the weak dependence of pre-constant value on the equivalence ratio. Hence the pre-constant value is fit for specific equivalence ratio based on the parametric variation study. The tuned AFSW model with fitted pre-constant specific to given equivalence ratio predicted are compared with experiments and discussed. The tuned AFSW model produced turbulent flame speed values which are good agreement with experiments.
35
A., Guessab, and Aris A. "A RANS/EDC Simulation of the Lifted Turbulent Non-Premixed Round Jet of CH4 Flame." WSEAS TRANSACTIONS ON HEAT AND MASS TRANSFER 17 (December 31, 2022): 206–13. http://dx.doi.org/10.37394/232012.2022.17.22.
Abstract:
The objectives of this work is to determine the average rate of reaction by numerical study of the reacting flow inside an axisymmetric free jet, and the validation of the eddy dissipation concept (EDC) combustion model implemented in ANSYS Fluent. The validation of the eddy dissipation concept combustion model involved the reproduction of a lifted, non-premixed, turbulent free jet flame described experimentally in Mahmud (2007). Three chemical mechanisms were used along the combustion model, namely the 2-step Westbrook and Dryer mechanism, the skeletal Jones-Lindstedt mechanism and the Hyer mechanism. Turbulence was modeled with the standard k-ε model The flame lift-off height and the temperature profiles are reproduced accurately by the Hyer model.
36
Bao, Jinrong, Chenzhen Ji, Deng Pan, Chao Zong, Ziyang Zhang, and Tong Zhu. "Investigation of Harmonic Response in Non-Premixed Swirling Combustion to Low-Frequency Acoustic Excitations." Aerospace 10, no. 9 (September 15, 2023): 812. http://dx.doi.org/10.3390/aerospace10090812.
Abstract:
The propagation mechanism of flow disturbance under acoustic excitations plays a crucial role in thermoacoustic instability, especially when considering the effect of non-premixed combustion on heat release due to reactant mixing and diffusion. This relationship leads to a complex coupling between the spatial distribution of the equivalence ratio and the propagation mechanism of flow disturbance. In the present study, the response of a methane-air non-premixed swirling flame to low-frequency acoustic excitations was investigated experimentally. By applying Proper Orthogonal Decomposition (POD) analysis to CH* chemiluminescence images, the harmonic flame response was revealed. Large Eddy Simulation (LES) was utilized to analyze the correlation between the vortex motion within the shear layers and the harmonic response under non-reacting conditions at excitation frequencies of 20 Hz, 50 Hz, and 150 Hz. The results showed that the harmonic flame response was mainly due to the harmonic velocity pulsations within the shear layers. The acoustically induced vortices within the shear layer exhibited motion patterns susceptible to harmonic interference, with spatial distribution characteristics closely related to the oscillation modes of the non-premixed combustion.
37
Marley, Stephen K., Eric J. Welle, and Kevin M. Lyons. "Combustion Structures in Lifted Ethanol Spray Flames." Journal of Engineering for Gas Turbines and Power 126, no. 2 (April 1, 2004): 254–57. http://dx.doi.org/10.1115/1.1688768.
Abstract:
The development of a double flame structure in lifted ethanol spray flames is visualized using OH planar laser-induced fluorescence (PLIF). While the OH images indicate a single reaction zone exists without co-flow, the addition of low-speed co-flow facilitates the formation of a double flame structure that consists of two diverging flame fronts originating at the leading edge of the reaction zone. The outer reaction zone burns steadily in a diffusion mode, and the strained inner flame structure is characterized by both diffusion and partially premixed combustion exhibiting local extinction and re-ignition events.
38
Lam Wai Kit, Hassan Mohamed, Ng Yee Luon, Hasril Hasini, and Leon Chan. "Modelling and Simulation of Micro Gas Turbine Performance and Exhaust Gaseous." Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 104, no. 2 (May 11, 2023): 184–95. http://dx.doi.org/10.37934/arfmts.104.2.184195.
Abstract:
Numerical simulation of cold flow and explosion in a Capstone C30 micro gas turbine is simulated using OpenFOAM. This study is aimed to investigate the combustion of non-premixed methane/air inside a micro gas turbine. The combustion characteristic inside a micro gas turbine with 100% methane is assumed for the fuel is studied with a three-dimensional model of micro gas turbine. The velocity of the flow increases significantly in the explosion simulation where the combustion of non-premixed methane/air mixture is initialised. The temperature in the micro gas turbine increased to 2400K at the downstream of inlets and reduces to 1500K at the combustion zone. High concentration of CO and CO2 is in the main reaction zone. The fraction of water vapours and hydroxyl on the other hand is lower compared to other species.
39
Xie, Tianfang, and Peiyong Wang. "ANALYSIS OF NO FORMATION IN COUNTER-FLOW PREMIXED HYDROGEN-AIR FLAME." Transactions of the Canadian Society for Mechanical Engineering 37, no. 3 (September 2013): 851–59. http://dx.doi.org/10.1139/tcsme-2013-0072.
Abstract:
Though hydrogen fuel reduces the carbon dioxide emission, it still produces NOx. However, gaps exist in the fundamental understanding of hydrogen-air combustion and the NO emission; most previous research has focused on the flames burning with mixture such as H2 mixed with CH4, rather than pure H2 flame. Here, a computational study is presented to investigate the stretch effect on NO formation in counter-flow premixed hydrogen-air flame. The simulation of premixed hydrogen flame was performed with OPPDIF code and UCSD chemical mechanism. Result indicates that the NO formation is affected by three factors: radical concentration, flame temperature, and residence time of reactants. The flame temperature, the reaction rate of NO, and the NO emission index all decrease when the stretch rate increases. Moreover, the formation of NO through thermal mechanism, NNH mechanism, and N2O mechanism is discussed, as well as the percentage of their contribution.
40
Mohammadi, Milad, and Mohammad Sadegh Abedinejad. "Analysis of NO Formation and Entropy Generation in a Reactive Flow." Aerospace 9, no. 11 (October 28, 2022): 666. http://dx.doi.org/10.3390/aerospace9110666.
Abstract:
A comprehensive investigation of turbulent combustion is accomplished to study the relationship between nitrogen oxide (NO) formation and entropy generation distribution in a non-premixed propane combustion. The radiation heat transfer and combustion are simulated, employing the discrete ordinates model and laminar flamelet model, respectively. A post processing model is employed to estimate the NO formation rate. The present results of NO species formation, mean temperature and velocity are compared with the existing experimental data, and good agreements are obtained. It is shown that the main region of total entropy generation rate and NO formation rate is at the same axial position. The entropy generation distribution may be defined as an index by which the combustion region and main region of NO formation are predicted. However, total entropy generation rate is more sensitive to high temperature (1500–1930 K) than that of NO formation rate. With an increase of 28.7% in temperature, the entropy generation and NO formation rates rise by 900% and 127%, respectively. The occurrence of chemical reactions plays the major role in the generation of entropy.
41
Anand, M. S., and F. C. Gouldin. "Combustion Efficiency of a Premixed Continuous Flow Combustor." Journal of Engineering for Gas Turbines and Power 107, no. 3 (July 1, 1985): 695–705. http://dx.doi.org/10.1115/1.3239791.
Abstract:
Experimental data in the form of radial profiles of mean temperature, gas composition and velocity at the combustor exit and combustion efficiency are reported and discussed for a swirling flow, continuous combustor. The combustor is composed of two confined, concentric independently swirling jets: an outer, annular air jet and a central premixed fuel-air jet, the fuel being propane or methane. Combustion is stabilized by a swirl-generated central recirculation zone. The primary objective of this research is to determine the effect of fuel substitution and of changes in outer flow swirl conditions on combustor performance. Results are very similar for both methane and propane. Changes in outer flow swirl cause significant changes in exit profiles, but, surprisingly, combustion efficiency is relatively unchanged. A combustion mechanism is proposed which qualitatively explains the results and identifies important flow characteristics and physical processes determining combustion efficiency. It is hypothesized that combustion occurs in a thin sheet, similar in structure to a premixed turbulent flame, anchored on the combustor centerline just upstream of the recirculation zone and swept downstream with the flow. Combustion efficiency depends on the extent of the radial propagation, across mean flow streamtubes, of this reaction sheet. It is concluded that, in general, this propagation and hence efficiency are extremely sensitive to flow conditions.
42
Ibrahim, Muhammad Hilmi, Norikhwan Hamzah, Mohd Zamri Mohd Yusop, Ni Luh Wulan Septiani, and Mohd Fairus Mohd Yasin. "Control of morphology and crystallinity of CNTs in flame synthesis with one-dimensional reaction zone." Beilstein Journal of Nanotechnology 14 (June 21, 2023): 741–50. http://dx.doi.org/10.3762/bjnano.14.61.
Abstract:
The growth of carbon nanotubes (CNTs) in a flame requires conditions that are difficult to achieve in a highly heterogeneous environment. Therefore, the analysis of the properties of the reaction zone within the flame is critical for the optimal growth of CNTs. In the present study, a comprehensive comparison between the CNT synthesis using a methane diffusion flame and a premixed flame is conducted regarding the morphology and crystallinity of the as-grown nanotubes. The premixed burner configuration created a flame that is stabilized through axisymmetric stagnation flow through sintered metal with one-dimensional geometry, different from a conventional co-flow flame. The significant difference in temperature distribution between the two flames causes a difference in the characteristics of the growth products. In the diffusion flame, the growth is limited to specific regions at certain height-above-burner (HAB) values with a temperature range of 750 to 950 °C at varying radial locations. The identified growth regions at different HAB values showed similar temperature distributions that yield CNTs of similar characteristics. Interestingly, the growth of CNTs in the premixed flame is dictated by only the HAB because the temperature distribution is relatively uniform along the radial directions but significantly different in the vertical direction. 17.3% variation in temperature in the axial direction successfully led to 44% and 66% variation in CNT diameter and crystallinity, respectively. The morphology control capability demonstrated in the present study is important for CNT functionalization for energy storage, nanosensor, and nanocomposite applications, where diameter and crystallinity are influential properties that govern the overall performance of the components.
43
Hrebtov, M. Yu, E. V. Palkin, D. A. Slastnaya, R. I. Mullyadzhanov, and S. V. Alekseenko. "Large-eddy simulation of a reacting swirling flow in a model combustion chamber." Journal of Physics: Conference Series 2119, no. 1 (December 1, 2021): 012031. http://dx.doi.org/10.1088/1742-6596/2119/1/012031.
Abstract:
Abstract We perform Large-eddy simulations of a non-premixed swirling flame in a model of a combustion chamber with a swirling air bulk flow at Re = 15000 and a central pilot low-velocity jet with methane using the Flamelet-generated manifold model. The unsteady behaviour of this regime is well reproduced based on the flame dynamics. The distribution of turbulent kinetic energy suggests the presence of intensive vortical structures typical of high-swirl flows similar to the precessing vortex core.
44
Avdonin, Alexander, Max Meindl, and Wolfgang Polifke. "Thermoacoustic analysis of a laminar premixed flame using a linearized reactive flow solver." Proceedings of the Combustion Institute 37, no. 4 (2019): 5307–14. http://dx.doi.org/10.1016/j.proci.2018.06.142.
45
Susilo, Sugeng Hadi, and Hangga Wicaksono. "Numerical analysis of NOX formation in CO2 diluted biogas premixed combustion." EUREKA: Physics and Engineering, no. 6 (November 18, 2021): 57–64. http://dx.doi.org/10.21303/2461-4262.2021.002072.
Abstract:
A further investigation of premixed biogas combustion towards the NOx formation is presented in this study. The purpose of the simulation is to determine the addition of CO2 in biogas fuel to the combustion behavior of premixed biogas on NOx formation, and to determine the occurrence of NOx in the pre-mixed biogas combustion. In this study, the Counterflow Premixed Flame class is used where this class is based on the One Dim class which is the basis for simulations with a 1-dimensional domain. The Counterflow Premixed Flame class uses an axisymmetric stagnation flow domain which has been written based on the equations. Cantera uses Newton's method to solve them. Completion is carried out in two stages. The first stage is to solve the solution using the equilibrium at each z coordinate point that has been determined. Many estimation starting points are determined from the start of the program. The second stage is the recalculation process at each point and then subdivided to get a smoother solution. The premixed excess CO2 biogas fuel and air combustion analyzed using a 1-dimensional numerical study. The diluted CO2 mass fraction ranged between 0–40 %. The CH4/CO2/air volume flow rate was maintained in ±L/min. The analysis implements the 1-D Counter Flow approach. Two counterflow nozzles were 20mm in diameter and the flame stagnation point at 10 mm. The results show that NOx mass fraction formed only on a fuel-lean mixture of CH4/CO2/air and its values decreased along with CO2 added. The addition of CO2 could reduce the NO species mass fraction down to 18 %, and NO2 reduction down to 7 %. This is mainly caused by a decreasing heat release rate of NO+N↔N2+O, N+O2↔NO+O, N+OH↔NO+H, and N+CO2↔NO+CO reactions. The N+CO2↔NO+CO reaction increased as CO2 was added but its values were not as much as the decline of three other reactions
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Zhang, Qun, Hua Sheng Xu, Tao Gui, Shun Li Sun, Yue Wu, and Dong Bo Yan. "Investigation on Reaction Flow Field of Low Emission TAPS Combustors." Applied Mechanics and Materials 694 (November 2014): 45–48. http://dx.doi.org/10.4028/www.scientific.net/amm.694.45.
Abstract:
A twin annular premixing swirler (TAPS) combustor model of low emissions was developed in this study. And computational studies on combustion process in the combustor model were carried out. Standard k-ε Turbulence Model, PDF non-premixed combustion model, Zeldovich thermal NOx formation model and DPM two-phase model were employed. The distributions of some key performance parameters such as gas temperature, flow velocity, concentrations of NOx and CO emissions were obtained and analyzed. At the same time, combustion mechanics inside the TAPS combustor model were investigated. The computational results indicated that the TAPS combustor employed in this study does a better job of improving key combustion performances such as combustion efficiency, total pressure recovery and outlet temperature distribution factor, and reducing NOx and CO emissions at the same time.
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Nie, Tao, Ping Zhang, Kun Yang, Lei Zhou, Xiangquan Zheng, and Li Luo. "Study on Laminar Combustion Characteristics of Ammonia/ Hydrogen Premixed Based on Chemical Reaction Kinetics." E3S Web of Conferences 406 (2023): 02031. http://dx.doi.org/10.1051/e3sconf/202340602031.
Abstract:
The combustion characteristics of ammonia/hydrogen premixed laminar flow and the effect of hydrogen on the combustion performance of ammonia fuel were studied. First, the corresponding model of ammonia/ hydrogen premixed laminar combustion is established by using GRI3.0 mechanism, Konnov mechanism, Mei mechanism, Okafor mechanism, and Otomo mechanism respectively. Second, the simulation results are compared with the experimental results. It is found that the Mei mechanism and Okafor mechanism are more suitable for ammonia/ hydrogen premixed laminar combustion. On this basis, the effects of equivalent ratio, hydrogen ratio, and initial temperature on laminar flame velocity, maximum combustion temperature, and NO mole fraction were studied. The results show that the laminar flame velocity, the maximum combustion temperature, and the mole fraction of NO first increase and then decrease with the increase of the equivalent ratio, and the laminar flame velocity reaches the maximum when the equivalent ratio is 1.1. At the same time, with the increase of hydrogen ratio and initial temperature, the maximum combustion temperature increases first and then decreases. The mole fraction of NO increased with the increase of hydrogen ratio and initial temperature. The results show that mixing hydrogen in ammonia can improve the combustion characteristics of ammonia.
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Stefanizzi, Michele, Saverio Stefanizzi, Vito Ceglie, Tommaso Capurso, Marco Torresi, and Sergio Mario Camporeale. "Analysis of the partially premixed combustion in a labscale swirl-stabilized burner fueled by a methane-hydrogen mixture." E3S Web of Conferences 312 (2021): 11004. http://dx.doi.org/10.1051/e3sconf/202131211004.
Abstract:
Nowadays hydrogen is gaining more and more attention by Industry, Academia and Politics. Being a carbon free fuel, it is supposed to have a key role in the future energy scenario, especially if produced by renewable sources. The use of mixtures of hydrogen and conventional hydrocarbons in gas turbines is one of the most promising technical solutions for obtaining a sustainable combustion during the transition toward a full decarbonization. For this reason, it is fundamental to investigate the behaviour of fuels enriched with hydrogen in combustion processes. In this work, a lab-scale swirled premixed burner has been investigated by means of a fully 3D URANS approach. Firstly, a numerical simulation with cold flow has been performed to validate the model against experimental data. Then, reactive flow simulations have been performed. Initially, a combustion with 100% methane was considered. Then, a 30% by volume hydrogen blending has been investigated. The partially premixed combustion model has been implemented to take into account the inhomogeneities of the mixture at the chamber inlet. The variation of the flame structure due to the hydrogen enrichment will be described in terms of the temperature and species concentration distributions.
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NICHOLS, JOSEPH W., and PETER J. SCHMID. "The effect of a lifted flame on the stability of round fuel jets." Journal of Fluid Mechanics 609 (July 31, 2008): 275–84. http://dx.doi.org/10.1017/s0022112008002528.
Abstract:
The stability and dynamics of an axisymmetric lifted flame are studied by means of direct numerical simulation (DNS) and linear stability analysis of the reacting low-Mach-number equations. For light fuels (such as non-premixed methane/air flames), the non-reacting premixing zone upstream of the lifted flame base contains a pocket of absolute instability supporting self-sustaining oscillations, causing flame flicker even in the absence of gravity. The liftoff heights of the unsteady flames are lower than their steady counterparts (obtained by the method of selective frequency damping (SFD)), owing to premixed flame propagation during a portion of each cycle. From local stability analysis, the lifted flame is found to have a significant stabilizing influence at and just upstream of the flame base, which can truncate the pocket of absolute instability. For sufficiently low liftoff heights, the truncated pocket of absolute instability can no longer support self-sustaining oscillations, and the flow is rendered globally stable.
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Bidabadi, Mehdi, Sadegh Sadeghi, Pedram Panahifar, Davood Toghraie, and Alireza Rahbari. "An asymptotic analysis for detailed mathematical modeling of counter-flow non-premixed multi-zone laminar flames fueled by lycopodium particles." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 4 (July 11, 2019): 2137–68. http://dx.doi.org/10.1108/hff-11-2018-0617.
Abstract:
Purpose This study aims to present a basic mathematical model for investigating the structure of counter-flow non-premixed laminar flames propagating through uniformly-distributed organic fuel particles considering preheat, drying, vaporization, reaction and oxidizer zones. Design/methodology/approach Lycopodium particles and air are taken as biofuel and oxidizer, respectively. Dimensionalized and non-dimensionalized forms of mass and energy conservation equations are derived for each zone taking into account proper boundary and jump conditions. Subsequently, to solve the governing equations, an asymptotic method is used. For validation purpose, results achieved from the present analysis are compared with reliable data reported in the literature under certain conditions. Findings With regard to the comparisons, although different complex non-homogeneous differential equations are solved in this paper, acceptable agreements are observed. Finally, the impacts of significant parameters including fuel and oxidizer Lewis numbers, equivalence ratio, mass particle concentration, fuel and oxidizer mass fractions and lycopodium initial temperature on the flame temperature, flame front position and flow strain rate are elaborately explained. Originality/value An asymptotic method for mathematical modeling of counter-flow non-premixed multi-zone laminar flames propagating through lycopodium particles.