The production of turbulent stress in a shear flow by irrotational fluctuations
The production of turbulent stress in a shear flow by irrotational fluctuations
复制标题
无旋波动在剪切流中产生湍流应力
作者：
I. Gartshore;P. Durbin;J. Hunt
本文研究了外部湍流如何影响初始无湍流区域，在该区域内存在平均速度梯度Du/Dz。快速扭曲理论说明了外部湍流如何在切变区引起无旋涨落，并与切变相互作用产生旋转速度涨落和平均雷诺应力。这些应力延伸到剪切区，距离约为L∞的整数量级。由于初始外部湍流和剪切流之间的实际锋面是一个随机扭曲的表面，因此靠近锋面的固定点的湍流是间歇性的。通过一个简单的统计模型将间歇性包括在本分析中。实验是在风洞中进行的，流动被从上游延伸到x=0的平板分割。在板块上方，网格产生了湍流。在板的下方，金属丝网产生了一个低湍流切变。板块(x>；0)的尾迹向下游衰减。在相互作用区观察到湍流剪应力从零增长到显著值。观测到的应力的大小和程度与预测相当吻合。我们得出的结论是，湍流应力可以由平均切变区的无旋涨落产生，并且这种影响可以用快速扭曲理论来估计。
This paper is a study of how external turbulence affects an initially turbulence-free region in which there is a mean-velocity gradient dU/dz. Rapid-distortion theory shows how external turbulence induces irrotational fluctuations in the sheared region, which interact with the shear to produce rotational velocity fluctuations and mean Reynolds stresses. These stresses extend into the sheared region over a distance of the order of the integral scale L∞. Since the actual front between the initial external turbulence and the shear flow is a randomly contorted surface, the turbulence of a fixed point near the front is intermittent. Intermittency is included in the present analysis by a simple statistical model. Experiments were done in a wind tunnel with the flow divided by a plate extending from upstream to x = 0. Above the plate, turbulence was produced by a grid. Below the plate a low turbulence shear was produced by wire screens. The wake of the plate (x > 0) decayed downstream. Turbulent shear stress was observed to grow from zero to significant values in the interaction region. The magnitude and extent of the observed stress agrees reasonably well with predictions. We conclude that turbulent stresses can be produced by irrotational fluctuations in a region of mean shear, and that this effect can be estimated using rapid-distortion theory.