Direct Numerical Simulations and Large Eddy Simulations of Unpremixed Turbulent Flames

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Turbulent, nonpremixed combustion is to be modeled using a combination of direct numerical simulation (DNS) and large eddy simulation (LES) approaches. The numerics will employ spectral collocation (Fourier transforms) and spectral element (Chebyshev transforms and P-type finite elements) techniques. The following physical issues will be investigated through DNS: flame tip dynamics near extinguishment, lifted flame structure and the validation of percolation theory applied to flame sheet "holes", and the coupling between the instantaneous values of a conserved scalar and its rate of dissipation in spatially developing turbulent flames. The LES work will be aimed at developing a subgrid turbulence closure using a scalar single-point probability density function, with application to a homogeneous turbulent flow undergoing a finite rate binary reaction. The main objects of this research are the effects of exothermic reactions on turbulence, application of the spectral-element method to compressible reacting turbulent flows, and application of LES to finite rate reacting turbulent flows. The results should identify shortcomings associated with some of the turbulence models presently in use and guide the way to improved techniques for closure, thus advancing our ability to reliably model more physically realistic combustion chamber flows.