SANDIA Flame D

Application Area 2: Combustion

Application Challenge AC2-09

Abstract

This document contains the specifications of the Application Challenge proposed by the team of the Institute of Thermal Machinery, Cz?stochowa University of Technology. This team performed LES predictions of the Sandia Flame D within the EU-project MOLECULES FP5, Contract N° G4RD-CT- 2000-00402. The computations were performed with the BOFFIN-LES code developed at Imperial College by the group of Professor W.P. Jones. The software for the Conditional Moment Closure model used in calculations was developed by Professor E. Mastorakos at Cambridge University and implemented in the BOFFIN-LES code by the team of the Institute of Thermal Machinery.

Sandia Flame D is a widely used test case for the validation of numerical models of non-premixed combustion. This flame is of the flamelet regime type in which a scale separation appears i.e. the smallest scales of the turbulent flow, the Kolmogorov scales, are significantly larger than the scales characteristic for the reaction zone. Such a flame facilitates the study of models of turbulence/chemistry interaction, allowing to separate the influence of turbulence and turbulence/chemistry interaction models from the influence of chemical kinetics models applied. Non-premixed combustion is limited by turbulent mixing and dominated by large scale structures. The quality of unsteady flow dynamics predictions seems to be crucial for the quality of the overall combustion process. Hence, within this document attention is restricted to LES calculations and neither RANS nor URANS predictions are included or analyzed.

   To evaluate the sensitivity of the  subgrid-scale-modeling  quality  on
   turbulent combustion predictions, two subgrid-scale models were tested:
   the classical Smagorinsky  model and the  dynamic   version.  Turbulent
   mixing features are then transmitted  to  the  reaction  front  through
   turbulence/combustion  interaction  models  that  also  influence   the
   overall  combustion  process  predictions.   As   turbulence/combustion
   interaction model, two different approaches were  studied:  the  simple
   and efficient steady flamelet model and the  more  advanced  simplified
   Conditional  Moment  Closure-CMC  (In  simplified  CMC  approach,   the
   convective terms in physical space were  neglected,  making  the  model
   very close to the unsteady flamelet approach).

   DOAPS for this type of reacting flow are  velocity,  mixture  fraction,
   temperature and species concentration  mean  and  fluctuating  profiles
   quantified by their local maxima.