Effect of Turbulence Parameter on Heat and Particle Diffusion in a Atmospheric Turbulenc

本文研究了由湍流剪切流发生器产生的R_λ=400 （Re_M =10^6 ~ 10^7）大尺度湍流中，湍流参数对热量和粒子扩散的影响。用热风速仪和i型冷、x型热线探头测量了其速度场和温度场。通过对速度和温度波动的统计分析，得到了热羽流的流向演化。(1)在风洞中观测了热羽的蜿蜒运动。平均温度的概率密度函数的变化符合泰勒扩散定理，实现了短时间扩散过程。(2)蜿蜒运动受大尺度湍流涡的影响。当热羽流向间距LI与纵向积分尺度基本一致时，LI在流向距离上没有变化。当热羽的展向长度等于横向积分尺度时，其扩散过程转变为长时间扩散过程。(3)与网格湍流场的热扩散相比，大尺度湍流场的热通量非常大，展向热输运非常活跃。结果表明，当Rλ=430时，扩散系数K=180cm2/s。

The present research aimed to examine the effect of turbulence parameter on heat and particle diffusion in a large-scale turbulence, R_λ=400 (Re_M =10^6〜10^7), generated by a turbulent shear flow generator. Its velocity and temperature fields were measured by a thermo-anemometer and a I-type cold-and X-type hot-wire probe. The streamwise evolution of thermal plume was obtained through statistical analysis on velocity and temperature fluctuations.(1) The meandering motion of thermal plume was observed in a wind tunnel. The variation of probability density function of mean temperature gave good agreement with the Taylor's diffusion theorem and short time diffusion process was realized.(2) The meandering motion was affected by the large-scale turbulent eddy. When the streamwise interval of thermal plume, LI, was almost same as the longitudinal integral scale, LI didn't change in the stremwise distance. When the spanwise length of the thermal plume equaled the lateral integral scale, its diffusion shifted to long time diffusion process.(3) Compared with thermal diffusion in a grid turbulence field, heat flux was extremely large and spanwise thermal transportation was very active in the large-scale turbulence. As a result, the diffusion coefficient was K=180cm2/s for Rλ=430.