高シュミット数物質噴流拡散場における条件付統計量の特性(流体工学,流体機械)

概要

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Characteristics of the conditional statistics such as the expected value of the velocity, scalar dissipation and Laplacian of scalar conditioned on concentration, i.e., <u_i|C^^〜 = ψ), <x|C^^〜 = ψ> and <◸^2c|C^^〜 = ψ>, are important because the transport equation of the probability density function of a passive scalar requires closure for these staistics. In this paper, we investigate such conditional statistics in an axisymmetric turbulent jet diffusion field of a high-Schmidt-number matter. A commercial dye (whose Schmidt number is about 3 800) is used as the diffusing fluid, and five different jet Reynolds numbers are chosen. Simultaneous measurements of the velocity and concentration have been made by a combined probe of X-type hotfilm and fiber-optic concentration sensor based on Lambert-Beer's law. It is found that <ιu|ψ> and <ψ> show a good linearity to the concentration fluctuation. The distributions of <x|ψ> have a flat shape on the jet centerline. On the other hand, at γ/b_u = 0.73 (bu : radial half-width of the axial mean velocity profile), they increase monotonically as ψ increases. It seems that the difference of these shapes is attributed to the shapes of concentration PDF. The distributions of <◸^2c|ψ> are consistent with the IEM model on the jet centerline. These conditional statistics remain nearly unaffected by the Reynolds number and Schmidt number.
2007-03-25