The response of a turbulent boundary layer to a step change in surface roughness. Part 2. Rough-to-smooth
The response of a turbulent boundary layer to a step change in surface roughness. Part 2. Rough-to-smooth
复制标题
湍流边界层对表面粗糙度阶跃变化的响应。
作者：
R.;E. R.
对从粗糙到光滑表面变化的下游增长的内层结构的实验研究表明，它与Antonia和Luxton（1971年B）对光滑到粗糙扰动情况的研究有本质的不同。内层的增长率小于光滑到粗糙的步骤，它似乎是更强烈的初始粗糙壁流决定了相当长的距离的扰动的扩散率。在内层内部，混合长度I相对于平衡分布I = KY增加。湍流能量收支表明，平流与生产或耗散相当，同时似乎有一些能量扩散到靠近壁的内层区域。边界层，作为一个整体，恢复慢得多以下的粗糙到平滑的变化比以下的平滑到粗糙的变化，并在最后一个测量站（16边界层厚度从光滑表面的开始）的平均速度和雷诺剪应力的分布是远离自我保存。
An experimental study of the structure of the internal layer which grows down-stream from a rough-to-smooth surface change shows it to be essentially different from that studied by Antonia & Luxton (1971 b) for the case of a smooth-to-rough perturbation. The rate of growth of the internal layer is less than that for the smooth-to-rough step and it appears that the more intense initial rough-wall flow dictates the rate of diffusion of the disturbance for a considerable distance. Inside the internal layer the mixing length I is increased relative to the equilibrium distribution I = KY. A turbulent energy budget shows that the advection is comparable with the production or dissipation, whilst there seems to be some diffusion of energy into the internal-layer region close to the wall. The boundary layer, as a whole, recovers much more slowly following a rough-to-smooth change than following a smooth-to-rough change, and at the last measuring station (16 boundary-layer thicknesses from the start of the smooth surface) the distributions of mean velocity and Reynolds shear stress are far from self-preserving.