逆圧力こう配乱流境界層における乱流諸量の基本特性

概要

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Measurements in boundary layers with 'moderate'to 'strong'adverse pressure gradients are presented and discussed. With increasing adverse pressure gradients, the velocity profile in U~ ~ ~ -^+ 〜 y^+ coordinates lies below the standard log law, thus indicating a reduction in the thickness of the sublayer. Correspondingly, the turbulence energy components as well as the Reynolds shear stress reduce in the near - wall region of the boundary layer. Waveforms of fluctuating velocity components in the boundary layer, especially in the near-wall region, are remarkably elongated in time in comparison with those in zero-pressure-gradient flows, and thus time scales increase with an increasing pressure gradient parameter P^+. The increase in time scales is not in proportion to the corresponding increase in the conventional viscous time scale ν/u^2_τ. It is found that the Taylor time scale is most appropriate to describe the essential characteristics of non-equilibrium adverse pressure gradient flows. Even the near wall-limiting behavior of streamwise velocity fluctuations for different P^+ is well correlated in the coordinates based on the Taylor time scale.
一般社団法人日本機械学会の論文
2000-06-25