Research Directions in Computational Mechanics (1991) / Chapter Skim
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10 Chemically Reacting Flow and Combustion
10 Chemically Reacting Flow and Combustion
Pages 99-107
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From page 99... ...
Even in a homogeneous chemical reaction between a simple hydrocarbon fuel and air, hundreds of elementary reactions occurring over time scales that cover orders of magnitudes are encountered. Most frequently, chemical reactions take place while transport processes (convection, diffusion, and radiation)
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From page 100... ...
In laminar combustion, where chemical kinetics is coupled with the transport of heat and mass by molecular diffusion, it is now possible, sometimes at a large cost, to compute the detailed structure and speed of propagation of laminar flames. The equations governing this problem are of the steady reaction-diffusion type, and progress in finite difference methods for one-dimensional initial and boundary value problems has allowed for accurate solution of these
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From page 101... ...
Spectral methods have mostly been applied to flows with simple boundary conditions. Recent progress in domain decomposition and global finite element discretization promises to lead to the application of spectral simulation to flows with complex boundaries.
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From page 102... ...
Methods that rely on multidimensional adaptive "ridding, such as adaptive projection methods; Lagrangian methods based on resolving the gradients of the gas dynamic variable, such as vortex and transport element methods; methods based on numerical asymptotic expansions; and hybrid methods that combine the convenience of kernel function discretization with spectrally accurate core functions should all be pursued for this purpose. It is important to mention that the problem of turbulence- combustion interactions -- the crux of turbulent combustion -- even in its most rudimentary form involving flame-strain and flame-vortex interactions, has not been satisfactorily explored due to the lack of powerful numerical schemes.
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From page 103... ...
However, these methods rely heavily on experimental input, and their theoretical foundations are not yet clear. Other phenomena, which have emerged from engineering applications of combustion and present research opportunities in the coming decade, include supersonic combustion involving shock wave reaction/front turbulence interaction (which is the mode of propulsion in the hypersonic transport vehicles)
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From page 104... ...
Hybrid methods, such as combined domain decomposition and interacting particle methods, also permit effective utilization of modern computer architecture (e.~.. medium and fine- grain parallel processing in which accurate.
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From page 105... ...
For example, as new materials are used in the production of stationary and mobile engines, it will be possible to increase the combustion temperature attained in these engines, which will call for analysis of high-temperature turbulent combustion stabilization and efficiency. Computational methods can substantially limit the time and cost required for such an analysis.
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From page 106... ...
Figure 10.1 shows results obtained by a method based on combining the better features of Lagrangian vortex methods and Eulerian finite element methods to study the evolution of a reacting shear layer in three-space dimensions.9 Besides being a canonical problem in turbulent combustion physics, reacting shear layers pose a severe challenge to computational methods since they possess all the properties that cause the breakdown of simple schemes: time-dependence, changing spatial length scales and overall topology, and the generation of strong strain fields and multiplicity of physical instabilities. Figure 10.1 shows the distortion of the computational grid, which also reveals the evolution of the reaction front as different modes of flow instability grow into their nonlinear stages, and confirms the adaptivity of the method.
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From page 107... ...
Flow and Combustion / ,-~ I ~ /1 ANY 1 = 4.0 1' t = 8.0 107 1 /~/ 1', the 12..
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