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首页> 外文期刊>Journal of Fluid Mechanics >EXPERIMENTS ON DENSITY-GRADIENT ANISOTROPIES AND SCALAR DISSIPATION OF TURBULENCE IN A STABLY STRATIFIED FLUID
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EXPERIMENTS ON DENSITY-GRADIENT ANISOTROPIES AND SCALAR DISSIPATION OF TURBULENCE IN A STABLY STRATIFIED FLUID

机译：稳定分层流体中密度梯度各向异性和湍流标量耗散的实验

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The anisotropic behaviour of density-gradient fluctuations in stably stratified grid turbulence and the consequences for simplified (isotropic) estimates of scalar dissipation rates chi were experimentally studied in a thermally stratified wind tunnel at moderate Reynolds numbers (Re-lambda similar or equal to 20). Strong stable stratifications were attained, with Brunt-Vaisala frequency N as high as 4 rad s(-1). The correlation method was used to estimate the mean-square cross-stream and streamwise density gradients. Cross-stream gradients were measured using two cold wires. The mean-square vertical gradients were found to become larger than the streamwise gradients by as much as a factor of 2.2 for the largest dimensionless buoyancy times (Nt = 7). This corresponds to a 40% error in the scalar dissipation estimates based on partial derivative theta/partial derivative x alone, and assuming the validity of the isotropic relations. Gradient spectral relations show that this buoyancy-induced anisotropy persists at all length scales. Better closure of the scalar variance balance was attained than in previously reported measurements by other researchers. This is attributed to our use of cold-wire temperature sensors having larger length-to-diameter ratio than used in the previous measurements. [References: 36]
机译：在中等雷诺数（Re-lambda近似或等于20）的热分层风洞中，通过实验研究了稳定分层网格湍流中密度梯度波动的各向异性行为以及简化的（各向同性）标量耗散率chi的估计结果。 。获得了强大的稳定分层，Brunt-Vaisala的频率N高达4 rad s（-1）。相关方法用于估计均方交叉流和流向密度梯度。使用两根冷线测量横流梯度。对于最大的无因次浮力时间（Nt = 7），发现均方垂直梯度比流向梯度大2.2倍。这对应于仅基于偏导数θ/偏导数x并假设各向同性关系有效的标量耗散估计中的40％误差。梯度光谱关系表明，这种浮力诱导的各向异性在所有长度尺度上都持续存在。与其他研究人员先前报告的测量结果相比，可以更好地关闭标量方差平衡。这归因于我们使用的冷线温度传感器的长径比比以前的测量值大。 [参考：36]

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