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.