スリットインゼクタによる乱流中への噴霧流のLES解析(<小特集>乱流研究の最前線)

概要

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Slit nozzles are used in some gasoline direct injection engines and make fan shaped spray. Spray injecting flows to turbulent flows from a slit nozzle have been analyzed numerically using combination of Large Eddy Simulation (LES) and lagrangian Discrete Droplet Method (DDM). As a result, LES can resolve the internal structure of the spray and irregular droplet distribution made by small eddies that momentum of spray itself induced. In conventional Reynolds Averaged Navier-Stokes (RANS) combined DDM calculation such eddies cannot be resolved, and also the internal spray structure or irregularity doesn't appear since all effects of turbulence are averaged. But such structure or irregularity is important for stable combustion in gasoline direct injection engines. Therefore the combination of LES and DDM method will play essential role for developing more robust and high efficient engines under wide operating conditions. We also proposed the way of constructing pseudo particle image in order to compare calculation results with sliced spray pictures obtained by experiments. We show time changes of the shape of brightness Probability Density Function (PDF) can be used to evaluate variance of spray droplets.
2006-12-25