反応性乱流拡散場における乱流拡散係数と乱流シュミット数

概要

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Eddy diffusivity Dtα and turbulent Schmidt number Sctα (α = A,B,R) in a planar liquid jet with a second-order chemical reaction (A+B → R) are experimentally investigated. Species A is premixed in the jet flow and species B is premixed in the main flow. The concentrations of reactive species and the streamwise velocity are simultaneously measured by combining I-type hot-film anemometry with an optical fiber probe based on the light absorption spectrometry. Eddy diffusivity and turbulent Schmidt number on the jet centerline are estimated from the results of the simultaneous measurements of concentration and velocity. The results show that the chemical reaction makes SctA large, and SctB has a negative value in the region where the mean concentration of species B decreases in the downstream direction whereas SctB for the nonreactive case has a positive value in the whole region on the jet centerline. It is also shown that SctR has a positive value in the upstream region whereas it has a negative value in the downstream region. The difference in SctB between the reactive and nonreactive cases becomes small in the downstream region. These results imply that the gradient diffusion model using the global constant turbulent Schmidt number poorly predicts the turbulent mass flux for reactive flows.