Fig 14 - uploaded by Jan Anker
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Computed temperature in the DLR combustor using the FGM (left) and the hybrid BML/flamelet model (right).
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The classical flamelet method, the new Flamelet Generated Manifolds method (FGM), and the hybrid BML/flamelet approach are assessed in the context of the Reynolds-averaged Navier-Stokes (RANS) equations on a large range of configurations for both gaseous and spray flames. The conceptual differences, advantages, and shortcomings of the models are di...
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Citations
... To model the dispersion and evaporation of the spray a Lagrangian method is used, whereas the flow is solved using an Eulerian approach. The combustion process is modelled using a tabulated chemistry approach, which has proven to yield reliable results [7] while being computationally efficient. In the current work, different strategies with respect to the modelling of the spray have been assessed. ...
... The classical flamelet method [27] is used since it is regarded as a reliable means to model non-premixed combustion processes and is found in most commercially distributed CFD codes. A detailed description can be found in the paper of Anker et al. [7]. ...
The use of Computational Fluid Dynamics (CFD) is now central to the design process of aero-engine combustors, enabling optimal, safe and stable operation, increased efficiencies, and the reduction of pollutant emission. To benefit maximally from the use of CFD it is essential to account for the relevant physical phenomena, in particular the fuel spray breakup and its evaporation. Different strategies for modelling the injection of fuel spray are applied - in the simplest approach the fuel is assumed to be gaseous upon injection, in the most advanced approach the fuel is modelled, using a Lagrangian-Eulerian approach, as a liquid spray which breaks up, evaporates and eventually burns inside the combustion chamber. The effects of the various modelling strategies on the flow, temperature, and compositional fields are investigated. The radial distribution of the simulated temperature field is compared to experimental data, demonstrating that acceptable accuracy is only achieved when the fuel is modelled as a liquid spray and a two-way momentum coupling between the spray and the gas-phase is accounted for.
... The idea of the method is to construct a manifold based on a set of flamelets. The implementation in FINE™/Open with OpenLabs™ is computationally efficient and it has also proven to yield reliable results for gas turbine and aero-engine combustors [27]. The manifolds are generated in a preprocessing step and stored in tables. ...
... where ρ denotes the density, u i the velocity vector, D the diffusion coefficient, and S c the source term of the progress variable. For turbulent flows an equation for the variance of the mixture fraction f is also solved and the combustion table is pre-integrated over the mixture fraction using a presumed -PDF [27]. The source term of the progress variable is determined as a linear combination of the reaction rate of the species according to the definition of the progress variable and stored in the FGM table. ...
... The FGM method in FINE TM /Open with OpenLabs TM has been validated on a large variety of elementary configurations and flames as well as industrial combustor geometries [27]. The compressible extension has been verified by comparing the results with the incompressible formulation for low-speed cases, a 1D-premixed flame as well as Sajben's transonic diffuser. ...
When turbomachinery systems are optimized, it is common to optimize each of the components separately from the others. While this approach allows the use of highly dedicated simulation tools, it does not account for the interactions between the different components. With the purpose to correctly capture the interaction between components, a novel, highly efficient, fully-coupled approach based on the Reynolds-Averaged Navier-Stokes equations (RANS) has been developed, enabling a steady or time-accurate simulation of a full aero-engine within a single code. One of the benefits of a steady, fully coupled approach over a steady component-by-component approach, is that the boundary conditions at the interfaces do not need to be guessed. As demonstrated in the paper, a fully coupled, time-accurate simulation has furthermore the advantage that the effect of the non-uniform temperature distribution at the outlet of the combustor is accounted for in the determination of the thermal field of the turbine. The combustion process is modelled using the Flamelet Generated Manifold (FGM) method. This approach is superior to classical tabulated chemistry approaches and it is computationally inexpensive since it only requires the solution of a few extra scalars and the look-up of a combustion table. The model has been extended so that high-speed compressible flows can be simulated and the potential effects between the combustor and the adjacent blade rows can be accounted for. The Nonlinear Harmonic (NLH) method is used to model the unsteady interactions between the blade rows as well as the influence of the inhomogeneities at the combustor outlet on the downstream turbine blade rows. Compared to conventional time-accurate RANS simulations (URANS), this method is two to three orders of magnitude faster and makes time-accurate turbomachinery simulations affordable. For a direct coupling between the different engine components a Smart Interface methodology is applied using the OpenLabs™ module. It allows the user to switch off the combustion model in the turbine and compressor blocks. With the aim of ensuring thermodynamic consistency between the different components of the engine, the same form of the energy equation is solved in all engine elements. Furthermore, the same thermodynamic coefficients, which are used to describe the reacting processes in the combustor, are used for a caloric description of the fluid in the compressor and turbine blocks. The thermodynamic data between the blocks is transferred via the Smart Interface and applied throughout the turbine and compressor blocks. The developed approach is described in detail and the potential of the novel full-engine methodology is exploited on the KJ66 micro-turbine gas engine case. The results of both the steady and the time-accurate fully coupled approaches are analyzed and the interaction between the different components of the KJ66 engine discussed.
... In the current work, the necessary FGM tables have been generated using TABGEN/Chemistry, which is a combustion table generation tool applying TU Eindhoven's 1D-chemistry code Chem1D. FGM tables can be generated either using premixed, non-premixed or igniting flamelets [30,31]. ...
With the increase of computational power, more sophisticated computational methods can be used, larger systems simulated, and complex phenomena predicted more reliably. Nevertheless, up to now, when turbomachinery systems are numerically optimized, each of the components, i.e., the compressor, combustor, and turbine, is simulated separately from the other two. While this approach allows the use of highly dedicated simulation tools, it does not account for the interactions between the different components.
With the purpose to meet the future requirements in terms of low emissions, high reliability and efficiency, a novel, highly efficient, fully-coupled, approach based on the Reynolds-Averaged Navier-Stokes equations (RANS) has been developed, enabling a steady or time-accurate simulation of a full aero-engine within a single code. One of the advantages of a steady, fully coupled approach over a steady component-by-component approach, is that the boundary conditions at the interfaces do not need to be guessed. A fully coupled, time-accurate simulation has furthermore the advantage that the effect of the non-uniform temperature distribution at the outlet of the combustor is accounted for in the determination of the thermal field of the turbine.
A Smart Interface methodology permits a direct coupling between the different engine components, compressor-combustor-turbine, and allows the Computational Fluid Dynamics (CFD) models to vary between each component within the same code. This allows the user to switch off, for instance, the combustion model in the turbine and compressor blocks.
For the simulation of the combustion process, the Flamelet Generated Manifold (FGM) method is applied. While the approach is superior to classical tabulated chemistry approaches and reliably captures finite-rate effects, it is computationally inexpensive since it only requires the solution of a few extra scalars and the look-up of a combustion table. The model has been extended so that high-speed compressible flows can be simulated and the potential effects between the combustor and the adjacent blade rows can be accounted for.
The Nonlinear Harmonic (NLH) method is used to model the unsteady interactions between the blade rows as well as the influence of the inhomogeneities at the combustor outlet on the downstream turbine blade rows. Compared to conventional time-accurate RANS simulations (URANS), this method is two to three orders of magnitude faster and makes time-accurate turbomachinery simulations affordable.
With the aim of ensuring thermodynamic consistency between the different components of the engine, the same form of the energy equation is solved in all engine elements. Furthermore, the same thermodynamic coefficients, which are used to describe the reacting processes in the combustor, are used for a caloric description of the fluid in the compressor and turbine blocks. The thermodynamic data between the blocks is transferred using the OpenLabs™ module.
The developed approach is described in detail and the potential of the novel full-engine methodology is exploited on the KJ66 micro-turbine gas engine case. The results of both the steady and the time-accurate, fully coupled approaches are analyzed and the interaction between the different components of the KJ66 engine discussed.
... Once the mixture fraction field is established, the temperature and the corresponding species concentrations can be determined by looking up in a flamelet or equilibrium table. The flamelet table was generated using the TABGEN/Chemistry [24] preprocessing tool. This tool determines the relation between the temperature/species compositions and the mixture fraction by computing a strained, 1D-diffusion flame. ...
... To improve the combustion modeling approach, it would be beneficial to substitute the flamelet method with the Flamelet Generated Manifolds (FGM) approach (Oijen and de Goey [22] and Gicquel et al. [23]), which is offered as one of many alternative modeling options in FINE TM /Open with OpenLabs TM . A recent study of Anker et al. [24] shows that FGM is superior to the flamelet method and delivers very reliable results for gasturbine and aero-engine applications. ...
The development of new generations of aircraft engines
with reduced environmental impact heavily relies on high-
fidelity 3D numerical analysis of the main engine components,
compressor, combustion chamber, turbine and their interactions,
including the transient and off-design behavior of the full engine.
Unlike component-by-component analysis, which requires
separate assumptions for the pressure and temperature boundary
conditions for each component, a fully coupled approach
requires only knowledge of the compressor inlet and turbine
outlet flow conditions. In addition, the engine rotation speed can
also be varied during the simulation to converge to the correct
balance of power between compressor and turbine.
This integrated approach provides a detailed description of
the flow field inside the full engine at the desired operating point
with one single CFD simulation.
The full engine simulation methodology can be developed
at several levels: (1) RANS simulations with mixing-plane
interfaces between components; (2) advanced RANS treatment
with inputs from the nonlinear harmonic (NLH) methodology to
allow for tangential non-uniformity, such as hot streaks entering
the turbine nozzle from the combustor; (3) inclusion of the
unsteady rotor-stator interactions, via NLH, in compressor and
turbine stages; (4) coupling with LES simulations in the
combustor.
This paper presents results from levels (1) and (2) of this
methodology applied to a micro-turbine gas engine including the
HP compressor, combustor, HP and LP turbines and the exhaust
hood. The geometry has been obtained from the redesign of the
KJ66 micro gas turbine engine using preliminary design tools.
The injection and burning of fuel inside the combustion chamber
are modeled with a simplified flamelet model. The paper
presents the approach and results of the full engine simulation;
as well as the initial steps towards level (3).
The use of Computational Fluid Dynamics (CFD) is now central to the design process of aero-engine combustors, enabling optimal, safe and stable operation, increased efficiencies, and the reduction of pollutant emission. To benefit maximally from the use of CFD it is essential to account for the relevant physical phenomena, in particular the fuel spray breakup and its evaporation. Different strategies for modelling the injection of fuel spray are applied - in the simplest approach the fuel is assumed to be gaseous upon injection, in the most advanced approach the fuel is modelled, using a Lagrangian-Eulerian approach, as a liquid spray which breaks up, evaporates and eventually burns inside the combustion chamber. The effects of the various modelling strategies on the flow, temperature, and compositional fields are investigated. The radial distribution of the simulated temperature field is compared to experimental data, demonstrating that acceptable accuracy is only achieved when the fuel is modelled as a liquid spray and a two-way momentum coupling between the spray and the gas-phase is accounted for.
