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首页> 外文期刊>Journal of Physical Oceanography >Laboratory Measurements of Differential Diffusion in a Diffusively Stable, Turbulent Flow
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Laboratory Measurements of Differential Diffusion in a Diffusively Stable, Turbulent Flow

机译：扩散稳定湍流中微分扩散的实验室测量

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Laboratory experiments were performed to determine the conditions under which differential diffusion occurs and to evaluate its effect on the mixing efficiency. Diffusively stable profiles of temperature and salinity were stirred steadily by horizontally oscillating vertical rods. The two-component stratification ensures that both scalars experience the same stratification and forcing, or Richardson and Reynolds numbers. The eddy diffusivities K_T and K_S, for temperature and salinity, were estimated by fitting theoretical solutions of diffusion equations to measured profiles, and the mixing efficiency was computed as the ratio of the potential energy change during a stirring interval to the work done in that interval. Differential diffusion occurred for ε_a/vN~2 < 300-500, where ε_a is an average dissipation rate computed from an integrated energy budget. The diffusivity ratio d = K_S/K_T varied between 0.5 and 1 in the range 50 < ε_a/vN~2 < 500. The experiments also show that differential diffusion can significantly affect the mixing efficiency. An important dimensionless parameter is the density ratio R_ρ, which is the ratio of the density change due to temperature to that due to salinity. Measurements in cases with low density ratio (R_ρ ≈ 0.25) and high density ratio (R_ρ ≈ 5) showed that the mixing efficiencies agreed well for weak stratification, or small Richardson number. For larger Richardson number, the efficiency for the high-density-ratio case exceeded that for the low-density-ratio case by as much as a factor of 1.5.
机译：进行实验室实验以确定发生差异扩散的条件并评估其对混合效率的影响。通过水平摆动垂直杆稳定搅拌温度和盐度的扩散稳定曲线。两部分分层可确保两个标量经历相同的分层和强制或理查森数和雷诺数。通过将扩散方程的理论解与实测曲线拟合来估算温度和盐度的涡流扩散率K_T和K_S，并以搅拌间隔期间的势能变化与该间隔内完成的功的比值来计算混合效率。 。当ε_a/ vN〜2 <300-500时发生微分扩散，其中ε_a是根据综合能量预算计算出的平均耗散率。扩散比d = K_S / K_T在0.5到1之间变化，范围为50 <ε_a/ vN〜2 <500。实验还表明，微分扩散会显着影响混合效率。一个重要的无量纲参数是密度比R_ρ，它是由于温度引起的密度变化与由于盐度引起的密度变化之比。在低密度比（R_ρ≈0.25）和高密度比（R_ρ≈5）的情况下进行的测量表明，混合效率对于弱分层或较小的Richardson数非常吻合。对于较大的Richardson数，高密度比情况的效率比低密度比情况的效率高1.5倍。

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