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This paper describes the time-filtered Navier-Stokes (TFNS) approach capable of capturing unsteady flow structures important for turbulent mixing in the combustion chamber and two different subgrid models used to emulate the major processes occurring in the turbulence-chemistry interaction. These two subgrid models are termed as LEM-like model and EUPDF-like model, respectively. Two-phase turbulent combustion in a singleelement lean-direct-injection (LDI) combustor is calculated by employing the TFNS/LEMlike approach as well as the TFNS/EUPDF-like approach. Results obtained from the TFNS approach employing these two different subgrid models are compared with each other, along with the experimental data, followed by more detailed comparison between the results of an updated calculation using the TFNS/LEM-like model and the experimental data. Acronym CFD= computational fluid dynamics DNS = direct numerical simulation LES = large-eddy simulation RANS = Reynolds-averaged Navier-Stokes approach URANS = unsteady RANS TFNS = time-filtered Navier-Stokes approach SGS = subgrid scale SFC = subfilter component FCP = filtering-control parameter LEM = linear-eddy mixing EUPDF = Eulerian probability density function LDI = lean-direct injection VBB = vortex-breakdown bubble PVC = precession vortex core IntroductionTogether with rig testing and diagnostics, combustion CFD is now a major tool for combustion technology development. It is being used to complement, and sometimes to substitute the rig test. This leads to reduced costs, deepened insight, and improved foresight. Nevertheless, high-fidelity simulation of liquid combustion in practical engineering devices remains an elusive target in spite of significant advances in combustion modeling and simulation over the past decade. The main difficulty lies in the fact that combustion operates at the intersection of fluid dynamics, fuel chemistry, and multi-phase physics. Consequently, in addition to high-fidelity models for turbulence, chemical kinetics, and liquid fuel atomization and transport, models for accurately accounting for their interactions also are required. Furthermore, these intricate physical and chemical phenomena are present throughout a broad range of time scales and length scales in engineering devices.Some of these modeling and simulation issues are discussed in the next section, followed by a description of the TFNS formulation for two-phase flow and the subfilter closure models in Section 3. In Section 4, we describe the estimation of the filtered, chemical-reaction source terms via two different subgrid models of turbulence-chemistry 1 Research Aerospace Engineer, Combustion Branch, Associate Fellow AIAA. 2 Research Aerospace Engineer, Combustion Branch, Member AIAA.

Level of Review: This material has been technically reviewed by technical management. This report is a formal draft or working paper, intended to solicit comments and ideas from a technical peer group.

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