From drag-reducing riblets to drag-increasing ridges
From drag-reducing riblets to drag-increasing ridges
复制标题
从减阻肋到增阻脊
DOI：
--
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发表时间：
2022
影响因子：
3.7
通讯作者：
B. Frohnapfel
中科院分区：
文献类型：
--
作者：
L. V. von Deyn;D. Gatti;B. Frohnapfel
摘要小的减阻脊和大的增阻脊是纵向不变的横向周期性表面结构，它们的不同之处仅在于它们的横向周期性和它们的粘性单位大小。由于它们不同的阻力行为，通常脊和脊被分开分析。通过实验研究不同尺寸的梯形凹槽表面，我们在统一的框架中系统地解决了从条纹状行为到脊状行为的转变。结构高度和横向波长的变化都是物理的，通过考虑八个不同的表面，并在其粘性缩放的形式，通过跨越大范围的体积雷诺数$Re_B$。有效的表面摩擦系数$C_f$是通过在湍流槽道流动装置中的压降测量来确定的，该装置是为精确的阻力测量而设计的。一个意想不到的丰富的阻力行为被揭开，其中不同的阻力制度区分取决于$l_g^+$的值，粘性缩放的平方根的槽面积。在著名的沟槽减阻区域（跨度高达l_g^+=17$）之后，是粗糙度函数U^+$随l_g^+$呈几何级数增加的区域，这表明在l_g^+\approximately 40$处存在明显的完全粗糙行为。进一步增加$l_g^+$导致完全粗糙区的明显偏离，并且首次报道了粗糙度函数${\rm \Delta} U^+$在$50< l_g^+<200$时的意外非单调行为。对于足够大的$Re_B$和$l_g$，它表明，一个单一的参数，类似于经典的水力直径，是足以描述的阻力行为的脊。我们发现，一个适当的定义的有效通道高度是至关重要的解释阻力行为。当在通道高度定义中考虑结构化表面的纵向突出高度时，层流表现出与平坦表面相同的$C_f（Re_B）$关系。因此，这种方法使我们能够辨别由湍流引起的$C_f$的修改。我们提供预测的相关性，充分粗糙制度和高雷诺数范围内的螺旋槽表面，成为可能，由于所选的通道高度定义。
Abstract Small drag-reducing riblets and larger drag-increasing ridges are longitudinally invariant and laterally periodic surface structures that differ only in the details of their lateral periodicity and their size in viscous units. Due to their different drag behaviour, typically riblets and ridges have been analysed separately. By studying experimentally trapezoidal-grooved surfaces of different sizes, we address systematically the transition from riblet-like to ridge-like behaviour in a unified framework. The structure height and lateral wavelength are varied both physically, by considering eight different surfaces, and in their viscous-scaled form, by spanning a wide range of bulk Reynolds number $Re_b$. The effective skin-friction coefficient $C_f$ is determined via pressure-drop measurement in a turbulent channel flow facility designed for accurate drag measurements. An unexpectedly rich drag behaviour is unveiled, in which different drag regimes are distinguished depending on the value of $l_g^+$, the viscous-scaled square root of the groove area. The well-known drag-reducing regime of riblets that spans up to $l_g^+=17$ is followed by a regime in which the roughness function ${\rm \Delta} U^+$ increases logarithmically with $l_g^+$, indicating an apparent fully rough behaviour up to $l_g^+\approx 40$. Further increase of $l_g^+$ leads to a clear departure from the fully rough regime, and an unexpected non-monotonic behaviour of the roughness function ${\rm \Delta} U^+$ for $50< l_g^+<200$ is reported for the first time. For sufficiently large $Re_b$ and $l_g$, it is shown that a single parameter, similar to the classical hydraulic diameter, is sufficient to describe the drag behaviour of ridges. We find that an appropriate definition of the effective channel height is crucial for interpreting the drag behaviour. When the longitudinal protrusion height of the structured surface is accounted for in the channel height definition, a laminar flow exhibits the same $C_f(Re_b)$ relation known for flat surfaces. This approach thus allows us to discern the modification of $C_f$ induced by turbulence. We provide predictive correlations for the fully rough regime and the high Reynolds number range of trapezoidal-grooved surfaces that become possible thanks to the chosen channel height definition.
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影响因子：
3.7
作者：
Clemens Chan-Braun;Manuel Garc'ia-Villalba;M. Uhlmann
通讯作者：
Clemens Chan-Braun;Manuel Garc'ia-Villalba;M. Uhlmann
阻力改变表面上的湍流的光滑壁状行为：统一的虚拟原点框架
DOI：
--
发表时间：
2020
期刊：
arXiv preprint
影响因子：
--
作者：
Ibrahim J I
通讯作者：
Ibrahim J I
影响因子：
3.7
作者：
T. Medjnoun;C. Vanderwel;B. Ganapathisubramani
通讯作者：
T. Medjnoun;C. Vanderwel;B. Ganapathisubramani
影响因子：
2.4
作者：
Gatti, Davide;Guettler, Andreas;Tropea, Cameron
通讯作者：
Tropea, Cameron