Abstracts

Topic: P. Dutta, Y. R. Sivathanu, and J. P. Gore (1997),

“Discrete Probability Function Method for the Calculation of Turbulent Particle Dispersion,”

AIAA Journal, vol. 35, No. 1, Technical Notes, pp. 200-202.

Dispersion of liquid drops in spray combustion systems is a critical parameter for high combustion efficiency. In modern lean-premixed-prevaporized (LPP) low NO* combustors, the design of premixers to achieve complete drop evaporation and fuel-air mixing prior to combustion is crucial to the success of such systems. Drop dispersion determines the residence time of the drop in the premixer, prescribes local boundary conditions for drop heat and mass transfer processes, and enhances interface area and fuel vapor concentration gradients to promote faster evaporation and molecular mixing. Thus, the performance of premixers in LPP combustion systems seems to be dispersion limited. Most dispersion calculations involve separated flow trajectory models, which require the simulation of a large number of particle trajectories to obtain statistically significant results and to reduce shot noise. Even with a large number of computational parcels, events with lower probability may not be adequately represented. These events can be important in LPP combustion systems that depend on burning everywhere at overall lean conditions. For example, excursions in the equivalence ratio due to the presence of a relatively small number of large drops can lead to large variations in global NO* emissions. These events, though rare, are responsible for almost all of the NO formation. In this Note, a discrete probability density (DPF) method is applied to drop dispersion calculations to provide accurate simulations with reduced statistical noise and to simulate the occurrence of rare events.