  Large eddy simulations with three-dimensional finite-volume Conditional
Moment Closure (CMC) model are performed for a hydrogen / nitrogen lifted flame
with detailed chemical meachanism. The emphasis is laid on the influences of
mesh resolution and convection scheme of finite-volume CMC model on predictions
of reactive scalar distribution and unsteady flame dynamics. The results show
that the lift-off height is underestimated and the reactive scalars (e.g.
temperature, H2 and OH) are over-predicted with coarser CMC mesh. It is also
found that further refinement of the CMC mesh would not considerably improve
the results. The time sequences of the most reactive and stoichiometric OH mass
fractions indicate that finer CMC mesh can capture more unsteady details than
coarser CMC mesh. Moreover, the coarse CMC mesh has lower conditional scalar
dissipation rate, which would promote the ealier auto-ignition of the flame
base. Besides, the effects of the convection schemes in the CMC equations on
the lifted flame characteristics are also investigated. It is shown that
different convection schemes lead to limited differences on the time-averaged
temperature, mixture fraction and species mass fractions. Moreover, the RMS
values of H2 and OH mass fractions show larger deviation from the measurements
with hybrid upwind and central differencing scheme, especially around the flame
base. Furthermore, the distributions of the numerical flux on the CMC faces
also show obvious distinction between the upwind scheme and the blending
scheme. The budget analysis of the individual CMC terms shows that a sequence
of CMC faces has comparable contributions with upwind scheme. However, with the
hybrid schemes, the instantaneous flux is dominantly from limited CMC faces.
The reactivity of a CMC cell is more easily to be affected by its neighbors
when the upwind scheme is used.
