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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.

本研究旨在研究内部重力波的转变过程，以阐明内部重力波塌陷过程中反梯度热通量的发生与湍流产生之间的关系。采用7根冷热丝耙子和多通道高精度热风速计系统对温度场和速度场进行多点同时测量。通过速度与温度脉动的相关分析，得到了内部重力波空间结构沿流向的变化。(1)随着内部重力波向下游发展，在Brunt-Vaisala频率N_B以下的频率范围内，垂直速度脉动w和温度脉动θ的能级显着增加。同时，w和θ之间的相干性增大，相位差由-π变为-π/2。(2)随着波幅沿流方向的增大，中心冷线与其他6个探头测得的温度波动相关性变大，在N_B以下频率范围内相位差趋近于零。(3)在波塌陷过程的初始阶段，高次谐波温度波动势能较大。是通过速度和温度波动之间的相互作用而发展起来的。然后，频率较高的随机分量间歇性地与尖峰波形混合在一起。(4)在内重力波波前破裂时，通过将谐波分量的势能转换为随机分量的动能，诱导负湍流产生对抗浮力，从而产生反梯度热流(5)两点空间相关测量结果表明，相位内部重力波的速度随着它们沿流向发展而增加。