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The purpose of this paper is to numerically investigate the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor using the commercial computational fluid dynamic (CFD) software ANSYS FLUENT. The first scope of the study aims to explicitly compare the predictive capabilities of two turbulence models namely Unsteady Reynolds Averaged Navier-Stokes and Scale Adaptive Simulation for a reasonable trade-off between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium(NEQ) effects caused by turbulent strain such as flame stretching.

Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases, respectively. The computing method includes a two-way coupling in which phase properties and spray source terms are interchanging between the two phases within each coupling time step. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane+toluene) are used as jet-A1 surrogates. The combustion model is based on the mean mixture fraction and its variance, and a presumed-probability density function is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the equilibrium (EQ) assumption and thereafter, detailed NEQ calculations through the steady flamelets concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1,045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0 using a sensitivity based method, Alternate Species Elimination.

Numerical results of the gas velocity, the gas temperature and the species molar fractions are compared with their experimental counterparts obtained from a steady state flame available in the literature. It is observed that, SAS coupled to the tabulated flamelet-based chemistry, predicts reasonably the main flame trends, while URANS even provided with the same combustion model and computing resources, leads to a poor prediction of the global flame trends, emphasizing the asset of a proper resolution when simulating spray flames.

The steady flamelet model even coupled with a robust turbulence model does not reproduce accurately the trend of species with slow oxidation kinetics such as CO and H2, because of the restrictiveness of the solutions space of flamelet equations and the assumption of unity Lewis for all species.

This work is adding a contribution for spray flame modeling and can be seen as an extension to the significant efforts for the modeling of gaseous flames using robust turbulence models coupled with the tabulated flamelet-based chemistry approach to considerably reduce computing cost. The exclusive use of a commercial CFD code widely used in the industry allows a direct application of this simulation approach to industrial configurations while keeping computing cost reasonable.

This study is useful to engineers interested in designing combustors of gas turbines and others combustion systems fed with liquid fuels.

The present paper is about numerical simulations of one‐ and two‐dimensional lean hydrogen combustion at an equivalence ratio of 0.7. The initial flat two‐dimensional flames show unstable behavior. The instabilities generate flame wrinkling and flame induced turbulence. As a result, cusp‐like structures arise that both merge and break up in new cusps. Therefore, physically, the laminar burning velocity associated to an adiabatic flat flame does not exist. Instead, a statistical effective burning velocity and flame width develop in which the cusp like structures and their effects are included. The purpose of this paper is to describe the phenomena with a reduced chemical approach.

Simulations are performed with detailed kinetics, to study the main properties and dynamics of the wrinkling. An attempt is made to reduce the chemistry employing flamelet generated manifolds to make a step towards large‐scale, low cost simulations, which are still able to capture the physics. Here the manifold was built of premixed flames with variations of stretch, unburnt temperature and equivalence ratio. A priori correlations are presented, together with results from actual reduced chemistry simulations.

It was found that with introduction of variation of equivalence ratio into the manifold the main physical phenomena are captured. Moreover, an effective inclusion of differential diffusion was succesfully tested and applied. Results of effective burning velocities and flame widths are presented.

The paper shows the potential of performing accurate simulations using the chemical reduction technique of flamelet generated manifolds for pure lean hydrogen flames.

The purpose of this paper is to investigate the development process of the fire whirl in the fixed-frame facility and focus on the impacts of the fire whirl’s vortex core on the formation and flame structure of the fire whirl.

The complex turbulent reacting flame surface is captured by the large eddy simulation turbulence closure coupled with two sub-grid scale (SGS) kinetic schemes (i.e. the chemistry equilibrium and steady diffusion flamelet). Numerical predictions are validated thoroughly against the measurements by Lei et al. (2015) with excellent agreements. A double maximum tangential velocity refinement approach is proposed to quantify the vortex cores’ instantaneous location and region, addressing the missing definition in other studies.

The numerical results show that the transition process of the fire whirl is dominated by the vortex core movement, which is related to the centripetal force. The unsteadiness of the fully developed fire whirl was found depending on the instantaneous fluctuation of heat release rate. The steady diffusion flamelet scheme is essential to capture the instantaneous fluctuation. Furthermore, the axial velocity inside the vortex core is the key to determining the state of fire whirl.

Due to intensive interactions between buoyant fires and ambient rotating flow, the on-set and formation of fire whirl still remain largely elusive. This paper focused on the transition process of fire whirl between different development stages. This paper provides insights into the transition process from the inclined flame to the fire whirls based on the centripetal force.

This paper presented and compared two SGS kinetic schemes to resolve the fire whirl development process and the unsteadiness of its vortical structures. The modelling framework addresses the shortcoming of previous numerical studies where RANS turbulence closure and simplified combustion kinetics was adopted. Numerical results also revealed the fire whirl transition process and its relationship to centripetal force.

This study aims to deal with the large eddy simulation (LES) of an ignition sequence and the resulting steady combustion in a swirl-stabilized liquid-fueled combustor. Particular attention is paid to the ease of handling the numerical tool, the accuracy of the results and the reasonable computational cost involved. The primary aim of the study is to appraise the ability of the newly developed computational fluid dynamics (CFD) methodology to retrieve the spark-based flame kernel initiation, its propagation until the full ignition of the combustion chamber, the flame stabilization and the combustion processes governing the steady combustion regime.

The CFD model consists of an LES-based spray module coupled to a subgrid-scale ignition model to capture the flame kernel initiation and the early stage of the flame kernel growth, and a combustion model based on the mixture fraction-progress variable formulation in the line of the flamelet generated manifold (FGM) method to retrieve the subsequent flame propagation and combustion properties. The LES-spray module is based on an Eulerian-Lagrangian approach and includes a fully two-way coupling at each time step to account for the interactions between the liquid and the gaseous phases. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for the flow field while the eddy diffusivity model is used for the scalar fluxes. The fuel is liquid kerosene, injected in the form of a polydisperse spray of droplets. The spray dynamics are tracked using the Lagrangian procedure, and the phase transition of droplets is calculated using a non-equilibrium evaporation model. The oxidation mechanism of the Jet A-1 surrogate is described through a reduced reaction mechanism derived from a detailed mechanism using a species sensitivity method.

By comparing the numerical results with a set of published data for a swirl-stabilized spray flame, the proposed CFD methodology is found capable of capturing the whole spark-based ignition sequence in a liquid-fueled combustion chamber and the main flame characteristics in the steady combustion regime with reasonable computing costs.

The proposed CFD methodology simulates the whole ignition sequence, namely, the flame kernel initiation, its propagation to fully ignite the combustion chamber, and the global flame stabilization. Due to the lack of experimental ignition data on this liquid-fueled configuration, the ability of the proposed CFD methodology to accurately predict ignition timing was not quantitatively assessed. It would, therefore, be interesting to apply this CFD methodology to other configurations that have experimental ignition data, to quantitatively assess its ability to predict the ignition timing and the flame characteristics during the ignition sequence. Such further investigations will not only provide further validation of the proposed methodology but also will potentially identify its shortfalls for better improvement.

This CFD methodology is developed by customizing a commercial CFD code widely used in the industry. It is, therefore, directly applicable to practical configurations, and provides not only a relatively straightforward approach to predict an ignition sequence in liquid-fueled combustion chambers but also a robust way to predict the flame characteristics in the steady combustion regime as significant improvements are noticed on the prediction of slow species.

The incorporation of the subgrid ignition model paired with a combustion model based on tabulated chemistry allows reducing computational costs involved in the simulation of the ignition phase. The incorporation of the FGM-based tabulated chemistry provides a drastic reduction of computing resources with reasonable accuracy. The CFD methodology is developed using the platform of a commercial CFD code widely used in the industry for relatively straightforward applicability.

The purpose of this paper is to review the applications of the chemical reactor network (CRN) approach for modeling the combustion in gas turbine combustors and classify the CRN construction methods that have been frequently used by researchers.

This paper initiates with introducing the CRN approach as a practical tool for precisely predicting the species concentrations in the combustion process with lower computational costs. The structure of the CRN and its elements as the ideal reactors are reviewed in recent studies. Flow field modeling has been identified as the most important input for constructing the CRNs; thus, the flow field modeling methods have been extensively reviewed in previous studies. Network approach, component modeling approach and computational fluid dynamics (CFD), as the main flow field modeling methods, are investigated with a focus on the CRN applications. Then, the CRN construction approaches are reviewed and categorized based on extracting the flow field required data. Finally, the most used kinetics and CRN solvers are reviewed and reported in this paper.

It is concluded that the CRN approach can be a useful tool in the entire process of combustion chamber design. One-dimensional and quasi-dimensional methods of flow field modeling are used in the construction of the simple CRNs without detailed geometry data. This approach requires fewer requirements and is used in the initial combustor designing process. In recent years, using the CFD approach in the construction of CRNs has been increased. The flow field results of the CFD codes processed to create the homogeneous regions based on construction criteria. Over the past years, several practical algorithms have been proposed to automatically extract reactor networks from CFD results. These algorithms have been developed to identify homogeneous regions with a high resolution based on the splitting criteria.

This paper reviews the various flow modeling methods used in the construction of the CRNs, along with an overview of the studies carried out in this field. Also, the usual approaches for creating a CRN and the most significant achievements in this field are addressed in detail.

Safety improvement and pollutant reduction in many practical combustion systems and especially in aero-gas turbine engines require an adequate understanding of flame ignition and stabilization mechanisms. Improved software and hardware have opened up greater possibilities for translating basic knowledge and the results of experiments into better designs. The present study deals with the large eddy simulation (LES) of an ignition sequence in a conical shaped bluff-body stabilized burner involving a turbulent non-premixed flame. The purpose of this paper is to investigate the impact of spark location on ignition success. Particular attention is paid to the ease of handling of the numerical tool, the computational cost and the accuracy of the results.

The discrete particle ignition kernel (DPIK) model is used to capture the ignition kernel dynamics in its early stage of growth after the breakdown period. The ignition model is coupled with two combustion models based on the mixture fraction-progress variable formulation. An infinitely fast chemistry assumption is first done, and the turbulent fluctuations of the progress variable are captured with a bimodal probability density function (PDF) in the line of the Bray–Moss–Libby (BML) model. Thereafter, a finite rate chemistry assumption is considered through the flamelet-generated manifold (FGM) method. In these two assumptions, the classical beta-PDF is used to model the temporal fluctuations of the mixture fraction in the turbulent flow. To model subgrid scale stresses and residual scalars fluxes, the wall-adapting local eddy (WALE) and the eddy diffusivity models are, respectively, used under the low-Mach number assumption.

Numerical results of velocity and mixing fields, as well as the ignition sequences, are validated through a comparison with their experimental counterparts. It is found that by coupling the DPIK model with each of the two combustion models implemented in a LES-based solver, the ignition event is reasonably predicted with further improvements provided by the finite rate chemistry assumption. Finally, the spark locations most likely to lead to a complete ignition of the burner are found to be around the shear layer delimiting the central recirculation zone, owing to the presence of a mixture within flammability limits.

Some discrepancies are found in the radial profiles of the radial velocity and consequently in those of the mixture fraction, owing to a mismatch of the radial velocity at the inlet section of the computational domain. Also, unlike FGM methods, the BML model predicts the overall ignition earlier than suggested by the experiment; this may be related to the overestimation of the reaction rate, especially in the zones such as flame holder wakes which feature high strain rate due to fuel-air mixing.

This work is adding a contribution for ignition modeling, which is a crucial issue in various combustion systems and especially in aircraft engines. The exclusive use of a commercial computational fluid dynamics (CFD) code widely used by combustion system manufacturers allows a direct application of this simulation approach to other configurations while keeping computing costs at an affordable level.

This study provides a robust and simple way to address some ignition issues in various spark ignition-based engines, namely, the optimization of engines ignition with affordable computational costs. Based on the promising results obtained in the current work, it would be relevant to extend this simulation approach to spray combustion that is required for aircraft engines because of storage volume constraints. From this standpoint, the simulation approach formulated in the present work is useful to engineers interested in optimizing the engines ignition at the design stage.

Ignition process is a critical issue in combustion systems. It is particularly important for reliability and safety prospects of aero-engine. This paper aims to numerically investigate the burner-to-burner propagation during ignition process in a full annular multiple-injector combustor and then validate it by comparing with experimental results.

The annular multiple-injector experimental setup features 16 swirling injectors and two quartz tubes providing optical accesses to high-speed imaging of flames. A Reynolds averaged Navier–Stokes model, adaptive mesh refinement (AMR) and complete San Diego chemistry are used to predict the ignition process.

The ignition process shows an overall agreement with experiment. The integrated heat release rate of simulation and the integrated light intensity of experiment is also within reasonable agreement. The flow structure and flame propagation dynamics are carefully analyzed. It is found that the flame fronts propagate symmetrically at an early stage and asymmetrically near merging stage. The flame speed slows down before flame merging. Overall, the numerical results show that the present numerical model can reliably predict the flame propagation during the ignition process.

The dedicated AMR method together with detailed chemistry is used for predicting the unsteady ignition procedure in a laboratory-scale annular combustor for the first time. The validation shows satisfying agreements with the experimental investigations. Some details of flow structures are revealed to explain the characteristics of unsteady flame propagations.

This paper aims to assess the sensitivity of numerical simulation results of turbulent reactive flow to the formulation of inlet boundary conditions. The analysis concerns the profiles of the mean velocity the turbulence kinetic energy k and its dissipation rate ϵ. It is intended to provide guidance to the determination of inlet conditions when only global flow data are available. This situation can be met both in simple laboratory experiments and in industrial full-scale applications, when measurements are either incomplete or infeasible, resulting in lack of detailed inlet data.

Two turbulence–chemistry interaction models were studied: eddy dissipation concept and partially stirred reactor. Three different velocity profiles and related turbulence statistics were applied to present feasible scenarios and their consequences. Simulations with the most appropriate inlet data were accompanied with profiles of turbulent quantities obtained with a proposed method. This method was contrasted to other approaches popular in the literature: the pre-inlet pipe and the separate cold flow simulations of a burner. The methodology was validated on two laboratory-scale jet flames: Delft Jet-in-Hot-Coflow and Sandia CHN B. The simulations were carried out with open source code OpenFOAM.

The proposed relations for turbulence kinetic energy and its dissipation rate at the inlet are found to provide results comparable to those obtained with the use of experimental data as inlet boundary conditions. Moreover, from a certain location downstream the jet, weakly dependent on the Reynolds number, the influence of inlet conditions on flow statistics was found to be negligible.

This work reveals the consequences of the use of rather crude assumptions made for inlet boundary conditions. Proposed formulas for the profiles for k and epsilon are attractive alternatives to other approaches aiming to determine the inlet boundary conditions for turbulent jet flows.

The paper aims to be a first step toward the efficient, yet accurate, solution of detailed combustion fields using the lattice Boltzmann (LB) method, where applications are still limited due to both the stiffness of the governing equations and the large amount of fields to solve.

The suggested methodology for model reduction is developed in the setting of slow invariant manifold construction, including details of the while. The simplest LB equation is used in order to work out the procedure of coupling of the reduced model with the flow solver.

The proposed method is validated with the 2D simulation of a premixed laminar flame in the hydrogen‐air mixture, where a remarkable computational speedup and memory saving are demonstrated.

Because of the chosen detailed LB model, the flow field may be described with unsatisfactory accuracy: this motivates further investigation in this direction in the near future.

A new framework of simulation of reactive flows is available, based on a coupling between accurate reduced reaction mechanism and the LB representation of the flow phenomena. Hence, the paper includes implications on how to perform accurate reactive flow simulations at a fraction of the cost required in the detailed model.

This paper meets an increasing need to have efficient and accurate numerical tools for modelling complex phenomena, such as pollutant formation during combustion.

This paper is to give an overview of freely available subject services providing information for chemists on the Internet. An attempt is made to differentiate between portals and other kinds of resources encountered on the Web. A definition of portals is given. Subject collections of general chemistry, analytical chemistry, environmental research, toxicology and patents are described. Internet chemistry portals can be regarded as a valuable addition to the traditional print and online information sources used by chemists.