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Investigation of Turbulence Production and Counter-Gradient Heat Flux in a Strongly Stably-Stratified Flow Field

强稳定分层流场中湍流产生和反梯度热通量的研究

基本信息

批准号：
15560138
负责人：
MAKITA Hideharu
金额：
$ 2.37万
依托单位：
Toyohashi Univ.of Tech.
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

The present research aimed to examine the transition process of internal gravity waves to clarify relationship between the occurrence of counter-gradient heat flux and turbulence production in the collapse process of the internal gravity waves. Multi-point simultaneous measurement was conducted on temperature and velocity fields by a rake of 7 cold-and hot-wires and a multi-channel high-precision thermo-anemometer system. Streamwise change in the spatial structure of the internal gravity waves was obtained through correlation analysis on the velocity and the temperature fluctuations.(1)As the internal gravity waves developed downstream, the energy levels of the vertical velocity fluctuation, w, and the temperature fluctuation, θ, remarkably increased in the frequency range below the Brunt-Vaisala frequency, N_B. At same time, the coherence between w and θ increased and its phase difference changed from -π to -π/2.(2)With streamwise increase in the amplitude of the waves, correlations between the temperature fluctuations measured by the center cold-wire and the other six probes became larger and their phase differences approached zero in the frequency range below N_B.(3)In the initial stage of the collapse process of the waves, higher harmonic temperature fluctuations with large potential energy developed through the interaction between the velocity and the temperature fluctuations. Then, random components with higher frequencies became to intermingle with spiky wave forms intermittently.(4)At the break down of the wave fronts of the internal gravity waves, the counter-gradient heat flux was generated as negative turbulence production was induced against buoyancy force by converting the potential energy of the harmonic components to the kinetic energy of random components(5)The result of two point spatial correlation measurement showed that the phase velocity of the internal gravity waves increased as they developed in the streamwise direction.

本研究旨在研究内重力波的过渡过程，以阐明内重力波坍缩过程中反梯度热通量的发生与湍流的产生之间的关系。采用7根冷热线和多通道高精度热风速计系统对温度场和速度场进行了多点同步测量。通过对速度波动和温度波动的相关分析，得到了内部重力波空间结构的流向变化。(1)随着内重力波向下游发展，在Brunt-Vaisala频率N_B以下的频率范围内，垂直速度波动的能级w和温度波动的能级θ显著增加。同时w与θ的相干性增强，相位差由-π变为-π/2。(2)随着波幅值沿流方向增大，中心冷丝测得的温度波动与其他6个探头的相关系数增大，在N_B以下频率范围内相位差趋近于零。(3)在波坍缩过程的初始阶段，通过速度与温度波动的相互作用，产生了具有大势能的高次谐波温度波动。然后，具有较高频率的随机分量开始间歇性地与尖波形式混合。(4)内重力波波阵面破裂时，将谐波分量的势能转化为随机分量的动能，在浮力作用下产生负湍流，从而产生反梯度热流。(5)两点空间相关测量结果表明，内重力波的相速度随其向流方向发展而增大。