摘要
实验研究了圆柱尾迹中相干结构对湍流平均量的影响.用一个X热线在距离圆柱体y/d=4测量参考信号,用X热线和冷线相结合的三线探头测量从x/d=10～40的圆柱绕流尾迹中的速度和温度脉动,用条件平均的方法研充圆柱绕流近尾迹中的相干结构,并对相干结构对动量和热量的湍流输运过程的影响进行初步分析.结果表明:相干结构对尾迹中速度的横向脉动影响最大;相干结构对湍流参数的影响随x/d的变化明显.该工作还对相干结构引起的湍动能产生率变成负和逆温度梯度输运现象做了定性的解释.
The structure of a two-dimensional turbulent wake of a circular cylinder has received significant attention by researchers due to coherent motions. Although the topology of the velocity field in the near and intermediate wakes has been studied in detail, corresponding investigations of the temperature field have not been made. In this study, One X-wire, fixed at 4d below the centre of the cylinder (d =12.7mm), was used in conjunction with the three-wire probe (combination of an X-wire plus a cold wire) in order to provide a phase reference for the signals from the three-wire probe, while the three-wire probe was used to measure the velocity fluctuations in the stream-wise and lateral directions, u and v, respectively, and the temperature fluctuation,θ across the wake. The phase average method was used to study the coherent structure of near wake in a cross flow. Contributions from coherent motion to the heat and momentum fluxes are quantified and discussed in the context of the topology of the velocity and temperature fields. The results point to significant differences between the manner in which vortices transport momentum and heat. And there is significant streamwise (different x/d) variations for the transport characteristics. It was also found that the coherent motion makes more contribution to v2 than to u2 and θ2. The coherent contribution to turbulent characteristics such as Reynolds stresses, heat flux, is varied significantly with the change of x/d. The location of the maximum in Θ+θ corresponds approximately to the location of the extremum in ω at all values of x/d. However, the close similarity between Θ+θ and ω at x/d = 10 quickly impairs at larger x/d, implying that temperature becomes a less effective marker of the vortices as x/d increases. In the alleyway between vortices, the coherent heat flux vector is mainly in a direction opposite to the velocity vector. It was also found that coherent motion can yield a Reynolds shear stress with a sign opposite to that of uv is responsible for the
出处
《力学学报》
EI
CSCD
北大核心
2002年第4期508-518,共11页
Chinese Journal of Theoretical and Applied Mechanics
关键词
相干结构
湍流特性
圆柱绕流近尾迹
逆梯度输运
相位平均
turbulent coherent structure, near wake of circular cylinder, momentum and heat transport, transport of negative gradient
