基于激光的分层环境燃烧的层流和湍流测量研究

Practical gas turbine engine combustors create extremely non-uniform
flowfields, which are highly stratified making it imperative that similar environments
are well understood. Laser diagnostics were utilized in a variety of stratified
environments, which led to temperature or chemical composition gradients, to better
understand autoignition, extinction, and flame stability behavior. This work ranged from
laminar and steady flames to turbulent flame studies in which time resolved
measurements were used.
Edge flames, formed in the presence of species stratification, were studied by
first developing a simple measurement technique which is capable of estimating an
important quantity for edge flames, the advective heat flux, using only velocity
measurements. Both hydroxyl planar laser induced fluorescence (OH PLIF) and particle
image velocimetry (PIV) were used along with numerical simulations in the
development of this technique. Interacting triple flames were also created in a laboratory
scale burner producing a laminar and steady flowfield with symmetric equivalence ratio
gradients. Studies were conducted in order to characterize and model the propagation
speed as a function of the flame base curvature and separation distance between the
neighboring flames. OH PLIF, PIV and Rayleigh scattering measurements were used in
order to characterize the propagation speed. A model was developed which is capable
of accurately representing the propagation speed for three different fuels. Negative edge
flames were first studied by developing a one-dimensional model capable of reproducing
the energy equation along the stoichiometric line, which was dependent on different
boundary conditions. Unsteady and laminar negative edge flames were also simulated
with periodic boundary conditions in order to assess the difference between the steady
and unsteady cases. The diffusive heat loss was unbalanced with the chemical heat
release and advective heat flux energy gain terms which led to the flame proceeding and
receding. The temporal derivative balanced the energy equation, but also aided in the
understanding of negative edge flame speeds. Turbulent negative edge flame velocities
were measured for extinguishing flames in a separate experiment as a function of the
bulk advective heat flux through the edge and turbulence level. A burner was designed
and built for this study which created statistically stationary negative edge flames. The
edge velocity was dependent on both the bulk advective heat flux and turbulence levels.
The negative edge flame velocities were obtained with high speed stereo-view
chemiluminescence and two dimensional PIV measurements.
Autoignition stabilization was studied in the presence of both temperature and
species stratification, using a simple laminar flowfield. OH and CH2O PLIF
measurements showed autoignition characteristics ahead of the flame base. Numerical
chemical and flow simulations also revealed lower temperature chemistry characteristics
ahead of the flame base leading to the conclusion of lower temperature chemistry
dominating the stabilization behavior. An energy budget analysis was conducted which
described the stabilization behavior.