Influence of Surface Anisotropy on Turbulent Flow Over Irregular Roughness
Influence of Surface Anisotropy on Turbulent Flow Over Irregular Roughness
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DOI：
10.1007/s10494-019-00074-4
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发表时间：
2019-11-20
影响因子：
2.4
通讯作者：
Jelly, Thomas O.
中科院分区：
文献类型：
--
作者：
Busse, Angela;Jelly, Thomas O.
采用直接数值模拟（DNS）方法研究了表面各向异性对粗糙壁湍流槽道近壁区的影响。使用表面生成算法合成了一组9个具有固定平均峰谷高度、近高斯高度分布和指定流向和展向相关长度的不规则粗糙表面。通过将表面各向异性比（SAR）定义为表面的流向相关长度和展向相关长度的比值，我们证明了具有强展向各向异性（SAR < 1）的表面与它们的流向各向异性（SAR > 1）等效表面相比，可以引起粗糙度函数Delta U+增加超过200%。此外，我们发现粗糙度函数Δ U+和SAR参数之间的关系近似遵循指数衰减函数。近壁流的统计响应研究使用“双平均”的方法，以区分形式诱导的“分散”应力从他们的湍流同行。外层的相似性恢复的平均速度亏损的配置文件，以及雷诺应力。分散应力在粗糙冠层内均达到最大值。只有流向分散应力达到相当于雷诺应力的水平，高SAR的表面达到最高水平的流向分散应力。雷诺应力各向异性也显示出明显的差异与强烈的流向各向异性的情况下，保持接近轴对称，杆状状态的所有壁法向位置相比，展向各向异性的情况下，雷诺应力各向异性张量的轴对称，盘状状态的粗糙度平均平面周围观察。总的来说，从这项研究的结果强调，由粗糙表面引起的阻力惩罚的表面形貌的强烈影响，并突出其影响的平均动量赤字在外部流以及雷诺数和分散应力的粗糙层。
The influence of surface anisotropy upon the near-wall region of a rough-wall turbulent channel flow is investigated using direct numerical simulation (DNS). A set of nine irregular rough surfaces with fixed mean peak-to-valley height, near-Gaussian height distributions and specified streamwise and spanwise correlation lengths were synthesised using a surface generation algorithm. By defining the surface anisotropy ratio (SAR) as the ratio of the streamwise and spanwise correlation lengths of the surface, we demonstrate that surfaces with a strong spanwise anisotropy (SAR < 1) can induce an over 200% increase in the roughness function Delta U+, compared to their streamwise anisotropic (SAR > 1) equivalent. Furthermore, we find that the relationship between the roughness function Delta U+ and the SAR parameter approximately follows an exponentially decaying function. The statistical response of the near-wall flow is studied using a "double-averaging" methodology in order to distinguish form-induced "dispersive" stresses from their turbulent counterparts. Outer-layer similarity is recovered for the mean velocity defect profile as well as the Reynolds stresses. The dispersive stresses all attain their maxima within the roughness canopy. Only the streamwise dispersive stress reaches levels that are comparable to the equivalent Reynolds stress, with surfaces of high SAR attaining the highest levels of streamwise dispersive stress. The Reynolds stress anisotropy also shows distinct differences between cases with strong streamwise anisotropy that stay close to an axisymmetric, rod-like state for all wall-normal locations, compared to cases with spanwise anisotropy where an axisymmetric, disk-like state of the Reynolds stress anisotropy tensor is observed around the roughness mean plane. Overall, the results from this study underline that the drag penalty incurred by a rough surface is strongly influenced by the surface topography and highlight its impact upon the mean momentum deficit in the outer flow as well as the Reynolds and dispersive stresses within the roughness layer.