LARGE-EDDY SIMULATION OF A NONPREMIXED REACTING JET - APPLICATION ANDASSESSMENT OF SUBGRID-SCALE COMBUSTION MODELS

Results from large eddy simulations (LES) and direct numerical simulat ions (DNS) of a two-dimensional, spatially developing, compressible pl anar free jet undergoing an idealized, exothermic, chemical reaction o f the type F+rOx-->(1+r)P are presented in order to assess several sub grid-scale (SGS) combustion models. Both a priori and a posteriori ass essments are conducted. The SGS turbulence model used is the dynamic S magorinsky model (DSM). Two classes of SGS combustion models are emplo yed in this study. These include the conserved scalar approach and the direct closure approach. Specifically, the SGS combustion models invo lve several forms of direct filtered reaction rate closures, including a scale similarity filtered reaction rate model (SSFRRM), and a mixin g controlled strained laminar framelet model (SLFM) in the form of the rmochemical state relationships, obtained from the DNS, and two assume d forms for the subgrid mixture fraction filtered density function (FD F). In general, LES results are in reasonable agreement with DNS resul ts and highlight the performance of the various SGS combustion models. In particular, in the context of the present study, it is found that: (1) the SLFM cases overpredict product formation due to their inabili ty to capture finite-rate chemistry effects (2) due to the relatively low values of the SGS mixture fraction variance in the flow under stud y, the SLFM results are not sensitive to the form of the assumed FDF; and (3) in comparison to the other models investigated. the SSFRRM com bustion model provides the best agreement with the DNS for product for mation. (C) 1998 American Institute of Physics.