Mean flow of turbulent boundary layers over porous substrates
Mean flow of turbulent boundary layers over porous substrates
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DOI：
10.1103/physrevfluids.7.094603
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发表时间：
2022-09
影响因子：
2.7
通讯作者：
L. B. Esteban;E. Rodríguez-López;M. Ferreira;B. Ganapathisubramani
中科院分区：
文献类型：
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作者：
L. B. Esteban;E. Rodríguez-López;M. Ferreira;B. Ganapathisubramani
本文给出了具有不同孔径()、渗透率()和厚度()的多孔壁(可渗透和粗糙)上湍流边界层的平均流动测量结果，测量范围包括摩擦雷诺数()和基于渗透率的雷诺数()。用浮子阻力天平测定了平均壁面剪应力，用热线风速仪测定了附面层分布。衬底渗透率增加了平均速度差的大小。使用修正的指示函数，假设von Karman常量为“普遍的”值)支持先前的结果，其中观察到强烈修正的对数区域。该指示函数还被用来估计零面位移()、粗糙度函数()和当量沙粒粗糙度()。在高雷诺数时，粗糙度函数数据塌陷到尼库拉得的完全粗略的渐近线上。然而，在低粗糙度雷诺数()下，我们观察到流动是过渡粗糙的，演化为Nikuradse类型的行为。每个基质的等效砂粒粗糙度似乎包括粗糙度和渗透率贡献。可以使用从不同厚度的相同衬底获得的数据来区分这两个贡献。这可能允许我们将多孔壁建模为粗糙和可渗透的壁的组合。
Mean-flow measurements of turbulent boundary layers over porous walls (permeable and rough) with varying pore size (), permeability () and thickness () are presented across a wide range of friction Reynolds numbers () and permeability based Reynolds numbers (). The mean wall shear stress was determined using a floating element drag balance and the boundary layer profiles were acquired using hot-wire anemometry. Substrate permeability is shown to increase the magnitude of the mean velocity deficit. The use of a modified indicator function, assuming “universal” values for von Karman constant) supports previous results where a strongly modified logarithmic region was observed. The indicator function was also used to estimate the zero-plane displacement (), the roughness function (), and equivalent sandgrain roughness (). At high Reynolds numbers, the roughness function data collapses on to the Nikuradse's fully rough asymptote. However, at low roughness Reynolds numbers (), we observe the flow to be transitionally rough, evolving with Nikuradse-type behavior. The equivalent sandgrain roughnessfor each substrate appears to include roughness and permeability contributions. These two contributions can be separated using data obtained from the same substrates with different thickness. This may allow us to model the porous wall as a combination of rough and permeable wall.