A Triantafyllidis

Conditional Moment Closure LES Modelling of an Aero-Engine Combustor at Relight Conditions

A Conditional Moment Closure (CMC) approach embedded in an LES CFD framework is presented for simulation of the reactive flow field of an aero-engine combustor operating at altitude relight conditions. Before application to the combustor geometry, the CMC model was validated on the standard lab-scale Sandia flame D. For the combustor simulation, a global mechanism for n-heptane was used along with a Lagrangian approach for the spray, to which a secondary break-up model was applied. The simulation modelled a multi-sector sub-atmospheric rig that was used to verify the altitude relight capability of the combustor. A comprehensive suite of diagnostics was applied to the rig test, including high-speed OH and kerosene PLIF as well as high speed OH* chemiluminescence. The CMC-based CFD simulation was able to predict well the position of the flame front and fuel distribution at the low pressure, low temperature conditions typical of altitude relight. Furthermore, the simulation of the ignition showed strong similarities with OH* chemiluminescence measurements of the event. An EBU-based LES was run too and showed to be unable to capture the flame front as well as the CMC model could. This work demonstrates that CMC LES can be an effective tool to support assessment of the relight capability of aero-engine combustors.Copyright

LES/CMC of Forced Ignition of a Bluff-Body Stabilised Non-Premixed Methane Flame

A Large Eddy Simulation/Conditional Moment Closure calculation of forced ignition of a turbulent bluff-body stabilised non-premixed methane flame is performed and the results are qualitatively investigated to assess the suitability of this model for highly transient combustion phenomena. The qualitative features of the flame expansion process agree with experimental findings. Quantitatively, the time for the establishment of the whole flame is under-predicted, which could be improved by using a finer CMC grid.