An experimental investigation of the vertical temperature structure of homogeneous stratified shear turbulence
An experimental investigation of the vertical temperature structure of homogeneous stratified shear turbulence
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DOI：
10.1017/s0022112000002111
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发表时间：
2000-12
影响因子：
3.7
通讯作者：
K. Keller;C. W. Atta
中科院分区：
文献类型：
--
作者：
K. Keller;C. W. Atta
在热分层风洞中，利用新的垂直温度快速测量方法研究了均匀分层剪切湍流的垂直温度结构。研究了梯度Richardson数Rig = N2/（dz/dz）2的六种情况，其中N是Brunt-Väisälä频率（N2 =（g/t/dz），范围为0.015 [les ] Rig [les ] 0.5.三到五百高分辨率的温度分布是由几个流向站的每一种情况下的钻机。这些测量是补充与标准的定点，欧拉测量流向和垂直速度波动和温度波动，并与八点垂直耙的温度探头使用标准的热线和冷线技术。垂直剖面的独特之处在于，它可以计算有效位能（APE）、索普尺度（LTh）和横周期通量（SDd），以及一维垂直波数温度谱。这些数量与欧拉测量的湍流动能（KE），势能（PE），和浮力通量进行了比较。据发现，一维垂直波数温度谱包含更多的能量在较小的尺度相比，水平谱，部分原因是剪切变形，这导致较大的均方垂直梯度的波动温度相比，均方水平梯度。剪切和分层的组合，特别是在湍流随演化而衰减的情况下，与仅剪切或仅分层相比，加速了向小尺度各向异性的演化。结果发现，在高度分层的情况下，diapycnal通量可以持续后，浮力通量已崩溃到可以忽略不计的值，这表明增强传热没有湍流混合。对于低Rig，大尺度垂直平流产生高的局部温度梯度和静态不稳定区域。与不稳定区域相关的是APE，对于分层最少的情况，APE相对于KE增长。对于高Rig，湍流演化为波浪状状态，包含一些反梯度通量和不稳定斑块。这种波浪状的状态具有更高的热通量效率比更湍流的状态，由于低的耗散，但相对较高的diapycnal通量。
The vertical temperature structure of homogeneous stratified shear turbulence is investigated using new rapid vertical temperature measurements in a thermally stratified wind tunnel. Six cases of gradient Richardson number, Rig = N2/(dŪ/dz)2, where N is the Brunt–Väisälä frequency (N2 = (g/t¯)dt¯/dz), are studied, spanning a range 0.015 [les ] Rig [les ] 0.5. Three- to five-hundred high-resolution temperature profiles are made for several streamwise stations for each case of Rig. These measurements are supplemented with standard fixed-point, Eulerian measurements of streamwise and vertical velocity fluctuations and temperature fluctuations and with an eight-point vertical rake of temperature probes using standard hot-wire and cold-wire techniques. Vertical profiles uniquely enable the computation of available potential energy (APE), Thorpe scales (LTh), and the diapycnal flux (ϕd), as well as one-dimensional vertical wavenumber temperature spectra. These quantities are compared with Eulerian measurements of turbulent kinetic energy (KE), potential energy (PE), and buoyancy flux. It is found that the one-dimensional vertical wavenumber temperature spectrum contains more energy at smaller scales compared to the horizontal spectrum, owing in part to shear distortion, which leads to larger mean square vertical gradients of fluctuating temperature as compared to mean square horizontal gradients. The combination of shear and stratification, especially for cases where the turbulence decays with evolution, accelerates the evolution toward small-scale anisotropy compared to just shear or just stratification. It is found that in highly stratified cases, the diapycnal flux can persist after buoyancy flux has collapsed to negligible values, indicating enhanced heat transfer without turbulent mixing. For low Rig, large-scale vertical advection creates both high local temperature gradients and regions of static instability. Associated with the regions of instability is APE, which grows relative to KE for the least stratified cases. For high Rig, the turbulence evolves to a wavelike state, containing some counter gradient fluxes and unstable patches. This wavelike state has higher heat flux efficiency than the more turbulent states owing to the low dissipation but relatively high diapycnal flux.