Name: visually based characterization of the incipient particle motion in regular substrates: from laminar to turbulent conditions
Uploaded: 2018-02-22T15:00:00.000+00:00
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Description: Watch this Scientific Journal Video about Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions at JoVE.com

作者感谢未知的裁判为宝贵的意见, 并 Sukyung 崔, Byeongwoo 和 Baekkyoung 的合作, 建立实验。这项工作得到了21的大脑釜山项目在2017年。

作者没有什么可透露的

我们提出了两种不同的实验方法来表征初始粒子运动作为沉积床几何的功能。为此, 我们使用一个由三角形或二次对称排列的球体的单层, 这种方法使几何参数简化为单个几何。在蠕变流量极限中, 我们描述了用旋转浮子诱导层流剪切流的实验方法, 如前研究39,40,41。初步实验表明, 初始运动保持独立于基底的有限尺寸效应, 如径向位置, 或与基体的上游边界的距离38。同样, 临界屏蔽号被发现独立于间隔范围内的相对流淹没, 介于2和12之间, 并且独立于 3 <img alt="Equation 71" src="/files/ftp_upload/57238/EQ/57238eq071.jpg"> <img alt="Equation 72" src="/files/ftp_upload/57238/EQ/57238eq072.jpg"> 38的之间的惯性。在这个值之上, 由于旋转板引发的二次流引起的干扰, 因此观察到临界屏蔽数的增加。此因素限制了手稿第一部分所述实验过程的最大. <img alt="Equation 72" src="/files/ftp_upload/57238/EQ/57238eq072.jpg">第二种实验方法旨在解决水力过渡和粗糙湍流流的问题。剪切应力是由低速风洞引起的。为了建立与基体的任何尺寸或边界效应无关的参数范围, 我们对湍流边界层进行了测量, 其距离前缘为50、80、110、140、170和200毫米。在 50, 80, 110 和200毫米, 边界层测量在4个不同的位置在宽度方向, 55, 65, 95 和125毫米从一个基体边界。在140和170毫米, 边界层测量在两个不同位置的宽度方向, 65 和95毫米从一个基板边界。所有测量都是在临界自由流速度条件下进行的, 用于在三角形衬底 (2.00 英寸 0.10) mm 珠上休息的 (5.00 英寸 0.25) 毫米玻璃珠. <img alt="Equation 73" src="/files/ftp_upload/57238/EQ/57238eq073.jpg">在80和200毫米之间的间隔范围内, 形状因子的范围介于1.3 和1.5 之间, 如湍流边界层57所预期的那样。速度剖面在同一个距离从领先的边缘是很好的一致, 揭示对数系数的变化从5% 到10% 独立的宽度方向。对协议描述中选定的参数范围进行了仔细的选择, 以确保临界屏蔽数保持独立于实验装置的任何边界效应。这对两种实验方法都适用。
初始运动的阈值取决于运动模式, 反过来是床的几何性质的函数, 如粒子的曝光。在高雷诺数下, 如果粒子高度暴露在流14、65中, 则可能会出现初始运动。但是, 对于几乎完全由邻居屏蔽的单个粒子, 提升可能是更合适的模式14。在层流条件下, 由于升力通常被忽略了16、17、40、44、45、66和滚动或滑动, 因此情况简化了。假定为初始运动的主要模式。为了正确刻画临界屏蔽数作为床身几何的功能, 必须首先对运动模式进行深入分析。为此, 我们记录了粒子运动, 我们使用了一个图像处理算法来计算珠子39的旋转角度。如果此值与图 2 (g)或图 3 (g)的初始范围中所描述的纯滚动的理论角度相匹配, 则可以使用 eq. 1 和 eq 8 来推断该协议的1和2节分别.该算法识别粒子位置和标记, 以研究旋转和滑动运动的最小的人干预。粒子的跟踪是基于一个精明的边缘探测器和霍夫变换。此组合已被证明为研究颗粒传输过程提供了一个健壮可靠的工具1,39,67,68。另一方面, 标记检测是以简单的灰度阈值为基础的。该算法的主要缺点是必须根据成像系统调整阈值。尽管该算法考虑了几何罚的标记, 但跟踪更容易受到不同阈值级别和光强度波动所造成的误差的影响, 例如, 从蓝色圆圈中可以看出, 这表明在图 3 (e)和3 (f)的快照中, 靠近珠子中心的标记的质心。为了进一步应用, 我们建议使用交叉相关技术来检测后续帧之间的标记位移。这可能使我们能够实现子像素分辨率69 , 并且可以在存在许多标记时改进角度的检测。
在文献中发现了粒子阈值的不同定义。在层流条件下, 如1节所考虑的那样, 临界屏蔽数作为运动开始的无量纲参数通常定义为在 Eq. 1,即具有特征剪切应力为<img alt="Equation 74" src="/files/ftp_upload/57238/EQ/57238eq074.jpg"> </img> 32,34 ,36,70。其他无量纲参数作为伽利略号也在层流流37中找到。然而, 这个选择似乎足够在更高的粒子雷诺数, 惯性比摩擦更相关。Eq 1 中给出的定义在爬行流限制中显得特别充分, 在这种极限下, 当几何参数简化为常规结构40时, 确定性建模方法是有效的。本声明与第1节中所述的实验系统所测量的5-7% 级的最大标准偏差一致。在步骤1.4.2.3 中估计的标准偏差, 描绘了与流变仪相关的随机误差, 以及由于基体或珠子尺寸的局部缺陷而引起的波动。请注意, 水动力力的波动不应再低于一。使用14µm 珠子之间的间隔的二次基板, 我们得到了一个临界屏蔽数等于 0.040, 0.00238。确定标准偏差时, 考虑到图 5、 i. e的所有单个度量值, 五个不同的运行为每个材料组合在三个不同的地方位置。对于标准偏差, 对于显示方法精度的其他基板配置, 可找到高达7% 的值。值得一说的是, 除了导线网格尺寸的偏差外, 基板有时还会出现较大的局部缺陷, 如固定珠已分离的空洞或高度的变化等。因此, 在开始测量之前, 建议对顶部和侧面摄像机进行目视检查。高分辨率激光3D 打印可用于在需要亚微米分辨率的进一步应用中建立基板。
当珠部分或完全暴露于湍流, 如2节所考虑的, 当我们试图识别初始粒子运动时, 必须考虑峰值湍流速度值及其持续时间的作用。脉冲14、71或能量判据62显示为经典盾牌标准的一个有价值的替代品。他们建议, 除了水动力, 流动结构的特征时间尺度必须正确参数71。为此, 得到时间平均值和平方均方速度的相同算法, 根据条件估计能量流事件的持续时间. <img alt="Equation 75" src="/files/ftp_upload/57238/EQ/57238eq075.jpg"> </img>对于<img alt="Equation 76" src="/files/ftp_upload/57238/EQ/57238eq076.jpg"> </img>图 4 (e)的说明性实验, 能量流事件的持续时间保持为1-2 毫秒. 如果使用的是 Eq 中所给出的拖动系数 10, 如 Vollmer 和 Kleinhans 200713或阿里和德伊 201620基于科尔曼的实验72, 修改后的保持在上一个值的上方, 并且测量的最大持续时间减少到约1.6 毫秒. 在任何情况下, 持续时间仍然远远低于10毫秒的顺序, 如前所述<img alt="Equation 77" src="/files/ftp_upload/57238/EQ/57238eq077.jpg">在水通道62中进行的 Valyrakis、Diplas et 等2013 的实验。此外, 该算法还确定了 Gabry、傅et 201473基于罗奇方法74所示的积分长度刻度。在距基材直径一半的距离上, 估计的宏观尺度长度约为1.5 毫米。已经证明, 能够触发初始运动的大多数能量事件应该具有大约四粒径62的特征长度。因此, 这一说法可能表明, 在我们的低速风洞诱发的高能事件无法触发初始运动。这与图 4(e)中所示的平均速度略高于临界值, 并与在实验中注意到的5毫米珠子无关, 而中的标准偏差小于 8%. <img alt="Equation 73" src="/files/ftp_upload/57238/EQ/57238eq073.jpg">在步骤 2.2. 5-2. 2.6 中计算出的中的标准偏差提供了与流动参数相关的随机波动的估计, 以及常规基板上的局部缺陷. <img alt="Equation 73" src="/files/ftp_upload/57238/EQ/57238eq073.jpg">对于直径为5毫米的氧化铝珠, 我们获得了一个等于 12.30 0.23 米/秒的. <img alt="Equation 73" src="/files/ftp_upload/57238/EQ/57238eq073.jpg">这标准偏差被确定考虑10个个体奔跑在三个不同的位置在同一个距离从领先的边缘。对于2毫米的珠子, 标准偏差增加到大约14%。考虑到这一结果, 我们决定将盾构准则与 Eq 8 中定义的临界屏蔽号结合使用。此外, 我们选择提供具有代表性的不确定性的临界屏蔽数的特定值, 而不是呈现夹带的可能性。有两个主要来源的不确定性在 Eq. 6 为了评估剪切速度: 和. <img alt="Equation 73" src="/files/ftp_upload/57238/EQ/57238eq073.jpg"> <img alt="Equation 78" src="/files/ftp_upload/57238/EQ/57238eq078.jpg"> </img>从测量的标准偏差推断出的相对不确定性. <img alt="Equation 73" src="/files/ftp_upload/57238/EQ/57238eq073.jpg">中的相对不确定度与湍流边界层的测量有关. <img alt="Equation 78" src="/files/ftp_upload/57238/EQ/57238eq078.jpg">在同一个距离从领先的边缘, 典型偏差在适应系数范围在5和10% 之间取决于风扇速度轮流取决于基体几何和珠密度。在最保守的分析中假定中的相对不确定性为 10%. <img alt="Equation 78" src="/files/ftp_upload/57238/EQ/57238eq078.jpg">因此, 根据实验的不同, 的不确定性范围介于7和18% 之间. <img alt="Equation 79" src="/files/ftp_upload/57238/EQ/57238eq079.jpg"> </img>图 5中的误差线在应用上述分析 (包括相对不确定的颗粒直径、空气和粒子密度) 后, 显示护盾编号的不确定性。
实验协议允许将初始粒子运动定性为不同流场中埋藏度的函数。使用常规几何图形简化几何因素到一个单一的几何, 并避免任何疑问的作用, 邻里。当珠子从初始位置移动到下一平衡点时, 初始运动的判据就满足了。图像处理算法的应用阐明了初始运动的模式。在以前的研究中使用了该协议1节所述的实验方法, 指出了在层流条件下, 局部床排列对初始运动的强烈影响38,39,40,41. 然而, 该系统仅限于3以下。在较高的 Re, 我们提出了一个新的实验方法, 使我们能够解决水力过渡和粗糙的湍流流的制度。有趣的是, 系统的湍流特性与简化的几何参数结合在一起, 使我们能够用临界屏蔽数来描述初始运动, 其中的不确定性范围介于14和25% 之间。我们只在40至150之间, 提出一些典型的申请例子。作为研究研究的未来范围, 必须在更广泛的范围内特别强调水力过渡流制度, 因为在文献中可获得较少的数据。同样, 在更大的埋葬程度的实验应该进行。这些结果可能被用作更复杂模型的基准。例如, 阿里和德伊2016最近提出的现实模型是基于一个障碍系数, 这是从实验结果推断出的, 只有紧密堆积的泥沙珠20。实验结果为较少暴露于流动的微粒在爬行的流动极限被解决可能触发模型的推断在更大的埋葬程度。此外, 所提出的实验方法可以让我们强调湍流相干结构在初始粒子运动中的作用, 并能很强地简化几何因子。这在文学中仍然是很不清楚的。

初始粒子运动在广泛的工业和自然过程中遇到。环境例子包括河流和海洋中泥沙运输的初始过程、河床侵蚀或沙丘形成等其他1,2,3。气力输送4, 清除污染物或清洗表面5,6是典型的工业应用, 涉及粒子运动的开始。
由于广泛的应用, 粒子运动的开始已经被广泛研究了一个世纪, 主要是在湍流条件下7,8,9,10,11, 12,13,14,15。已有许多实验方法用于确定运动起始的阈值。研究内容包括粒子雷诺数13、16、17、18、19、20、相对流淹没等参数。21,22,23,24或几何因素作为静止的角度16,18,25, 暴露于流26,27,28,29,相对谷物凸起29或流向床斜率30。
包括湍流条件在内的阈值的当前数据大致分散12、31 , 结果通常看起来不一致24。这主要是由于在湍流条件下控制或确定流参数的固有复杂性13,14。此外, 泥沙运动的阈值强烈取决于运动模式,即滑动, 滚动或提升17和特征的初始运动31的标准。后者在侵蚀沉积床上可能不明确。
在过去十年中, 实验研究人员研究了层流流中的初始粒子运动32,33,34,35,36,37,38,39,40,41,42,43,44, 其中避免了与床交互的宽范围的长度刻度,45。在许多实际的情况下, 暗示沉淀, 粒子是相当小的, 粒子雷诺数保持低于约 546。另一方面, 层流可以产生像涟漪和沙丘一样的几何图案, 如湍流流做42,47。这两种方案中的班扬都反映了在基础物理47中的类比, 因此对粒子传输的重要洞察力可以从一个更好的受控实验系统48中获得。
在层流中, Charru et . 注意到, 均匀大小的珠子颗粒床的局部重排, 所谓的床装甲, 导致运动开始的门槛逐渐增加, 直到饱和条件达到32. 然而, 根据实验设置3644, 在不规则排列的沉积层中, 文献揭示了饱和条件的不同阈值。这种散射可能是由于对沉积物的定向、凸出层和致密性等粒子参数的控制困难所致。
本手稿的主要目的是详细描述如何将单个球体的起动作为水平沉积床几何性质的函数来刻画。为此, 我们使用常规几何, 由固定珠的单分子膜按照三角形或二次构型定期排列。类似于我们使用的常规衬底在微流控分析中的粒子模板组装 (49)、受限结构几何50或内部粒子诱导的 microdevices 的自组装等应用中发现。在微51中传输。更重要的是, 使用常规的衬底, 我们可以突出的影响, 地方几何和方向, 并避免任何 dubiety 的作用, 邻里。
在层流中, 我们观察到, 临界屏蔽数增加了 50%, 这取决于基体球体之间的间距, 从而使珠子暴露在流38上。类似地, 我们发现, 临界屏蔽号由两个因素所改变, 取决于基板的方向与流向38的方向。我们注意到, 不动的邻居只影响移动珠的开始, 如果他们比大约三粒径41。在实验结果的触发下, 我们最近提出了一个严格的分析模型, 可以预测爬行流限制40中的临界屏蔽数。该模型涵盖了从高暴露到隐藏珠的运动开始。
本手稿的第一部分论述了以往研究中所使用的剪切雷诺数的实验程序的描述, 再到1。层流是由旋转流变仪与平行配置引起的。在这个低雷诺数限制, 粒子不应该经历任何速度波动20和系统匹配所谓的水力平滑流, 其中粒子被淹没在粘性子层。
一旦形成层流的初始运动, 湍流的作用就会变得更加清晰。在这个想法的驱使下, 我们介绍了一个新的实验程序在第二部分的协议。采用开放射流试验段的哥廷根低速风洞, 可以在很大范围内确定临界屏蔽数, 包括水力过渡流和湍流体系。实验结果可以提供重要的洞察力和扭矩如何作用的粒子由于湍流流动取决于基体几何。此外, 这些结果可以作为一个基准, 为更复杂的模型在高 Re * 以类似的方式, 过去的工作在层流已经被用来养活半概率模型52或验证最近的数字模型53。我们提出一些典型的应用实例, 从40到150不等。
从初始平衡位置到下一粒子的运动, 建立了起始判据。图像处理用于确定运动开始的模式,即滚动、滑动、提升39、41。为此, 检测到手动标记的移动球体的旋转角度。该算法跟踪标记的位置, 并将其与球体的中心进行比较。在两个实验装置中进行了初步的实验, 阐明了临界屏蔽数与设置和相对流淹没的有限尺寸效应无关。实验方法的设计, 以排除任何其他参数依赖的关键盾号超越再 * 和几何性质的泥沙床。使用不同的流体-粒子组合来改变重复 *。临界屏蔽号的特征是埋葬程度的函数,, 由. <img alt="Equation 01" src="/files/ftp_upload/57238/57238eq001.jpg"> </img> 37作为<img alt="Equation 03" src="/files/ftp_upload/57238/57238eq003.jpg"> , <img alt="Equation 02" src="/files/ftp_upload/57238/57238eq002.jpg">其中是养神的<img alt="Equation 04" src="/files/ftp_upload/57238/57238eq004.jpg">角度,即54的运动发生的临界角, 是曝光度, 定义为实际暴露于流中的横截面积的比值。移动珠的总横截面积。

<table><tbody><tr><td>MCR 302 Rotational Rheometer</td><td>Anton Paar</td><td>Induction of shear laminar flow</td><td></td></tr><tr><td>Measuring Plate PP25</td><td>Anton Paar</td><td>Induction of shear laminar flow</td><td></td></tr><tr><td>Peltier System P-PTD 200</td><td>Anton Paar</td><td>Keep temperature of silicon oils constant in the system at laminar flow</td><td></td></tr><tr><td>Silicone oils with viscosities of approx. 10 and 100 mPas</td><td>Basildon Chemicals</td><td>Fluid used to induced the shear in the particles</td><td></td></tr><tr><td>Soda-lime glass beads of (405.9 &amp;plusmn; 8.7) &amp;mu;m</td><td>The Technical Glass Company</td><td>Construction of the regular substrates for laminar flow conditions</td><td></td></tr><tr><td>Opto Zoom 70 Module 0.3x-2.2x</td><td>WEISS IMAGING AND SOLUTIONS GmbH</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>2 x TV-Tube 1.0x, D=35 mm, L=146.5 mm</td><td>WEISS IMAGING AND SOLUTIONS GmbH</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>UI-1220SE CMOS Camera</td><td>IDS Imaging Development Systems GmbH</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>UI-3590CP CMOS Camera</td><td>IDS Imaging Development Systems GmbH</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>Volpi IntraLED 3 - LED light source&amp;nbsp;</td><td>Volpi USA</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>Active light guide diameter 5mm</td><td>Volpi USA</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>300 Watt Xenon Arc Lamp</td><td>Newport Corporation</td><td>Imaging system for recording the bead motion in the rheometer</td><td></td></tr><tr><td>Wind-tunnel with open jet test section, G&amp;ouml;ttingen type&amp;nbsp;</td><td>Tintschl BioEnergie und Str&amp;ouml;mungstechnik AG</td><td>Induction of turbulent flow</td><td></td></tr><tr><td>Glass spheres of (2.00 &amp;plusmn; 0.10) mm</td><td>Gloches South Korea</td><td>Construction of the regular substrates for turbulent flow conditions</td><td></td></tr><tr><td>Alumina spheres of (5.00 &amp;plusmn; 0.25) mm</td><td>Gloches South Korea</td><td>Targeted bead for experiments</td><td></td></tr><tr><td>CTA Anemometer DISA 55M01</td><td>Disa Elektronik A/S&amp;nbsp;</td><td>Measurement of&amp;nbsp; flow velocity in the wind tunnel</td><td></td></tr><tr><td>Miniaure Wire Probe Type 55P15</td><td>Dantec Dynamics</td><td>Measurement of&amp;nbsp; flow velocity in the wind tunnel</td><td></td></tr><tr><td>HMO2022 Digital Oscilloscope, 2 Analogue. Ch., 200MHz</td><td>Rohde &amp;amp; Schwarz</td><td>Measurement of&amp;nbsp; flow velocity in the wind tunnel</td><td></td></tr><tr><td>Phantom Miro eX1 High-speed Camera</td><td>Vision Research IncVis</td><td>Imaging system for recording the bead motion in the wind-tunnel</td><td></td></tr><tr><td>Canon ef 180mm f/3.5 l usm macro lens</td><td>Canon</td><td>Imaging system for recording the bead motion in the wind-tunnel</td><td></td></tr><tr><td>Table LED Lamp</td><td>Gloches South Korea</td><td>Imaging system for recording the bead motion in the wind-tunnel</td><td></td></tr></tbody></table>

visually based characterization of the incipient particle motion in regular substrates: from laminar to turbulent conditions

本文提出了两种不同的实验方法来确定粒子运动的阈值, 作为从层流到紊流条件下的床的几何性质的函数。为此, 在规则基板上研究了单个珠的起动运动, 这些基体由均匀大小固定球体的单层组成, 它们定期排列在三角形和二次对称中。阈值以临界屏蔽数为特征。运动开始的判据被定义为从原来的平衡位置到相邻的位移。用成像系统识别位移和运动方式。层流是使用旋转流变仪与平行磁盘配置诱导。剪切雷诺数保持在1以下。采用开放射流试验剖面, 在低速风洞中诱导湍流流动。风机用变频器调节风速。速度剖面是用一个与热膜风速计连接的热导线探头来测量的。剪切雷诺数范围在40和150之间。利用罗塔所提出的对数速度定律和修正后的墙法, 从实验数据中推断出剪切速度。当移动珠部分暴露于所谓的水力过渡流体系中的湍流流动时, 后者是特别感兴趣的。剪切应力是在运动开始时估计的。结果表明, 在两种体制下, 静力角的影响很大, 而珠对剪切流的暴露也有代表性。

图 1(a)表示用于描述爬行流限制中的临界护盾编号的实验设置示意图, 该协议1节。测量是在旋转流变仪中进行的, 为这个特定的应用进行了修改。一个直径为70毫米的透明有机玻璃板被仔细地固定在直径为25毫米的平行板上。测量系统的惯性因此在测量之前被调整了。一个定制的圆形容器, 直径为176毫米, 具有透明的墙壁, 与流变仪同心耦合。在前面部分进行了垂直切口。显微镜幻灯片被仔细地固定在前部, 以改善成像。调整间隙设置剖面以考虑容器的存在。在开始测量前, 板速最小化接近流体界面, 避免了珠运动。在该系统中, 单个珠可以从顶部通过透明板进行光学跟踪, 请参阅图 1(b), 或从侧面通过透明壁, 请参阅图 1(c)。在旋转板和基体之间产生剪切流剖面。因此, 临界剪切速率由提供. <img alt="Equation 48" src="/files/ftp_upload/57238/57238eq048.jpg"> </img>因此, 临界屏蔽数和剪切雷诺数可以定义为 eq. 1 和 eq 2 分别。协议2节中使用的设置在图 1(d)中进行了说明。测量是在一个定制的低速风洞与开放喷气试验区, 哥廷根类型进行。19 x 25 cm2的常规衬底位于测试部分的中间。风扇速度和因而流体速度由连接到鼓风机风扇的变频器调控。湍流边界层被诱导在规则基底之上。速度剖面用一个专门设计用于测量边界层的热导线微型探头来测量 (参见图 1(e)), 并将其与恒温风速计 (CTA) 耦合在一起。壁法线位置y由垂直阶段控制, 可在约0.01 毫米内重新定位。该位置用数字电平指示器测量, 分辨率为0.01 毫米。在完全粗糙的湍流机制 (通常是重 > 70), 剪切速度可以推断从一个适当的实验数据到对数墙定律, Eq. 559。在水力过渡机制中, 从适合于修改后的墙体定律推导出剪切速度, Eq 758。临界屏蔽数和剪切雷诺数可从8和 eq 9 分别表达的剪切速度得到。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57238/57238fig1.jpg"> 图 1: 在层流条件下使用的实验设置示意图(a). (405.9 @ 8.7) µm 直径的移动珠, 它们分别从顶部 (b) 和侧面 (c) 上, 由相同大小的球体组成, 其间距为14µm。在湍流条件下使用的实验设置示意图 (d)。两个移动珠子 (3.00 英寸 0.15) 毫米和 (5.00 英寸 0.25) mm 休息在一个二次基板上没有间距 (2.00 英寸 0.10) mm 接近微型热导线探头 (e)。探头放置在距基体球体顶部约0.05 毫米的距离。图 1(d)是从 Agudo et . 2017a39中复制的, 并获得了该发布的许可。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57238/57238fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
在以前的研究中开发了一个分析标记珠的图像处理例程39来计算运动开始时珠的旋转角度。图 2和图 3描述了在层流、re * = 0.06 和湍流条件下的适用性示例, 分别为87.5。使用有标记的球体, 我们得到了相同的临界屏蔽号, 对于无标记的珠子在测量不确定范围内。在精明的边缘检测和霍夫变换的基础上, 该程序能够识别出1.2 和 4%39之间的相对不确定度的珠子。旋转角由基于灰度阈值的跟踪标记确定。在这种情况下, 不确定性会增加到从7°到17°的绝对值, 这取决于成像系统39。图 2(a) - (f)中的快照说明了单个玻璃珠 (405.9 µm 8.7) 的代表性例子, 从初始平衡位置到下一个二次基板上的一个相同的珠子大小与14µm 之间的差距在球体之间。视频已从顶部通过透明测量系统记录, 如第1节所述 (见步骤 1.2.3)。图 2(g)显示在位移过程中旋转的角度, 它是沿基板弯曲轨迹的函数 (请参见<img alt="Equation 49" src="/files/ftp_upload/57238/57238eq049.jpg"> 图 2(g)的插入)。在两个平衡位置 () 之间的曲线路径上, 轨迹被归一化为珠线所移动的距离. <img alt="Equation 50" src="/files/ftp_upload/57238/57238eq050.jpg"> </img>图 2(g)中的虚线表示纯滚动的角度。单珠经历的总旋转 (140 8.5) °, 这与纯滚动运动的角度重合, 这也具有近似140°的价值。因此, 滚动是初始运动和 Eq 的模式. 1 可以用来表征初始粒子运动。
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57238/57238fig2.jpg"> 图 2: 在一个标记的珠子 (405.9 µm 8.7) 的初始运动中的快照在二次衬底上, 其间距为14µm, 在大约 0.06(a)-(f)。红十字会和绿线代表球体的中心, 并分别从算法获得的珠轮廓。蓝色圆圈表示标记的几何中心的轨迹。从左向右流动。快照是从 Agudo et al (2017)39中复制的, 并获得了该发布的许可。沿两个平衡位置 (g) 的曲线轨迹函数的旋转角。在关系图中指示快照的时间实例。虚线表示纯滚动运动的旋转角度。图 2(g)从 Agudo et al (2014)41中复制, 并获得了该发布的许可。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57238/57238fig2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
图 3(b) - (e)中的快照描绘了一个例子, 其中氧化铝珠的 (5 英寸 0.25) 毫米取代四位的一个二次基板由球体 (2.00 英寸 0.10) 毫米和它们之间无间隙。视频已从侧面记录, 如第2节 (见步骤 2.2. 1-2. 2.4)。测量的角度同意理论一在大约前二平衡位置的路径 (参见图 3(g))。因此, 轧制被认为是初始运动和 Eq 的模式. 8 可用于计算临界屏蔽数。然而, 在第二个平衡位置之后, 测量的旋转角似乎偏离了纯滚动运动。图 3(f)中的红线表示在基板上大约17个位置的较长路径中的珠轨迹。从弹道上可以看出粒子是如何在其沿基底运动过程中经历小飞行的。
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57238/57238fig3.jpg"> 图 3: 在二次基板上的标记珠 (5.00 英寸 0.25) 毫米直径的初始运动过程中的快照, 在大约87.5 个球体之间无间距的情况下,(a)-(e)。红十字会和绿线代表球体的中心, 并分别从算法获得的珠轮廓。蓝色圆圈表示标记的几何中心的轨迹。红色十字架在 (f) 代表珠中心的轨道沿大约17个位置沿基体。从左向右流动。旋转角度作为曲线轨迹的函数沿四平衡位置 (g)。在关系图中指示快照的时间实例。虚线表示纯滚动运动的旋转角度。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57238/57238fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
图 4(a)说明了方波测试, 用于估计在临界自由流速下的 CTA 在 (5 0.25) 毫米的氧化铝珠 (见步骤 2.3.5) 上的频率响应。电压下降 97%, 所需的时间约为0.1 毫秒. 因此, 由<img alt="Equation 51" src="/files/ftp_upload/57238/57238eq051.jpg"> </img> <img alt="Equation 52" src="/files/ftp_upload/57238/57238eq052.jpg"> </img> 60提供的频率响应结果大约为7.7 赫。从图 4(a)可以看出, 低于仍然远远低于峰值响应的15%。这表明热丝 CTA 参数 (包括过热率) 正确适应61。说明性示例的校准曲线显示在图 4(b)之前 (红色方块) 和速度剖面 (黑色圆圈) 的测量之后。两条曲线相互重叠, 表示实验期间未发生任何更改。对于 (5 英寸 0.25) 毫米的氧化铝珠, 在图 4(c)和4 (d)中, 时间平均速度和根平方速度绘制为规范化的壁法线组件的函数。它们是按照从2.5.1 到2.6.1 的步骤所描述的那样获得的。两种速度均以临界自由流速度正常化。从的最大值可以看出, 所测的粘性子层厚度约为0.25 毫米. <img alt="Equation 32" src="/files/ftp_upload/57238/57238eq032.jpg"> </img>图 4(c)中的实线表示符合实验数据的对数速度定律, Eq. 5, 而蓝线代表的数据适合根据罗塔20提出的修正速度定律,58, Eq 7。在这种情况下, 两种配合都是很好的协议, 因为粘性子层代表的移动珠直径的5%。因此, 从两种拟合得到的剪切速度不到8%。图 4(e)说明了由 Valyrakis et 等. 201362所述的能源标准角度出发的波动力对初始运动的作用。该实线显示瞬时流向速度的立方体的时间历史的一部分,, 测量在距离的一半移动氧化铝珠直径从基体. <img alt="Equation 53" src="/files/ftp_upload/57238/57238eq053.jpg"> </img>在这个特定的测量中, 速度以 25 kSa 的采样速率存储。蓝线表示平均速度的立方体,. <img alt="Equation 54" src="/files/ftp_upload/57238/57238eq054.jpg"> </img>红色虚线表示在 Valyrakis et 201163中计算的临界速度的立方体。
<img alt="Equation 55" src="/files/ftp_upload/57238/57238eq055.jpg">(10)
<img alt="Equation 57" src="/files/ftp_upload/57238/57238eq057.jpg">其中, 是流体力学质量系数, 大约等于 1, 在我们的实验中, 是假定为0.9 的拖动系数, <img alt="Equation 56" src="/files/ftp_upload/57238/57238eq056.jpg">如 Valyrakis et . 201163中所考虑的那样。和分别计算为 Eq 11 和12所示. <img alt="Equation 58" src="/files/ftp_upload/57238/57238eq058.jpg"> </img> <img alt="Equation 04" src="/files/ftp_upload/57238/57238eq004.jpg"> </img>瞬时流功率是速度62的立方体的线性函数。因此, 如果这些流事件的持续时间超过了<img alt="Equation 53" src="/files/ftp_upload/57238/57238eq053.jpg"> 62, 则在临界值之上的上的峰值可能被视为初始粒子运动的潜在触发器。自开发的算法通过在整个实验中评估与水平线的交集来估计能量流事件的持续时间. <img alt="Equation 53" src="/files/ftp_upload/57238/57238eq053.jpg"> <img alt="Equation 59" src="/files/ftp_upload/57238/57238eq059.jpg">在图 4中描述的演示实验中, 能量流事件的持续时间为1-2 毫秒, 最大值为2.1 毫秒。
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57238/57238fig4.jpg"> 图 4: 具有代表性的结果, 在低速风洞试验段中, 在不带间距的二次基板上休息的氧化铝珠 (5 英寸 0.25) mm 的运动开始时, 获得了典型的效果(a) CTA 在方波测试 (b) 校准曲线之前 (红色方块) 和速度剖面 (黑色圆圈) 测量后的频率响应。实线表示与数据匹配的第三个多项式趋势。拟合系数在图 (c) 时间平均流向速度剖面的嵌入中描述。实线和蓝色符号根据对数和修改后的壁律分别表示拟合 (d) 在小高度范围内的根均方根流向速度剖面。测量的粘性子层约0.25 毫米 (e) 瞬时流向速度立方体的时间历史的一部分, 测量在距离的一半移动氧化铝珠直径从基体。蓝线表示时间平均流向速度的立方体。红色虚线表示在 Valyrakis et 201164中计算的临界速度的立方体。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57238/57238fig4large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
图 5(a)表示临界护盾编号依赖项, 它是由 <img alt="Equation 60" src="/files/ftp_upload/57238/57238eq060.jpg"> </img> 37定义为2009的埋葬程度的函数。标记为红色的符号是从协议中的示例中获得的阈值。在我们的常规结构中, 静止角和曝光度是几何耦合的。养神的角度可以分析计算如下:
<img alt="Equation 61" src="/files/ftp_upload/57238/57238eq061.jpg">(11) 其中, 上标引用三角形几何, 引用在球体之间有间距的二次几何. <img alt="Equation 62" src="/files/ftp_upload/57238/57238eq062.jpg"> </img> <img alt="Equation 63" src="/files/ftp_upload/57238/57238eq063.jpg"> <img alt="Equation 64" src="/files/ftp_upload/57238/57238eq064.jpg">同样, 暴露度被定义为横截面积的流动产生:
<img alt="Equation 65" src="/files/ftp_upload/57238/57238eq065.jpg">(12) 其中, 是在有效零级和垂直轴之间的珠子曲面之间的角度 (请参见<img alt="Equation 66" src="/files/ftp_upload/57238/57238eq066.jpg"> </img>图 5的插入)。对于具有间距的三角形和二次基板, 可以显示: <img alt="Equation 64" src="/files/ftp_upload/57238/57238eq064.jpg">
<img alt="Equation 67" src="/files/ftp_upload/57238/57238eq067.jpg">(13) 其中是基板顶部下面的有效零级别 (请参见<img alt="Equation 68" src="/files/ftp_upload/57238/57238eq068.jpg"> 图 5的插入)。在蠕变流量极限中, 数值模拟表明, 有效零电平与间距: 线性增加. <img alt="Equation 64" src="/files/ftp_upload/57238/57238eq064.jpg"> </img> <img alt="Equation 69" src="/files/ftp_upload/57238/57238eq069.jpg"> </img>在较大的 Re * 中, 假定有效的零级为常量, 如德伊德<img alt="Equation 70" src="/files/ftp_upload/57238/57238eq070.jpg"> et 等. 201264所示。在40和150之间的重复范围内, 利用修改后的墙体法推断出剪切应力, 其中包括水力过渡流体系。实线和虚线是与实验数据相适应的功率趋势。如图 5所示, 临界屏蔽数随埋藏程度的增加而增大, 这表明部分屏蔽粒子对剪切流的影响很大。这包括比较三角形和二次基板的配置和不同的移动珠直径。沉积床几何的影响在较高的 Re 上似乎更明显。在相同的凸起程度上, 在1以下的临界护盾数仍远远高于40至150之间的重度值。
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57238/57238fig5.jpg"> 图 5: 临界护盾号对从层流到紊流条件的埋藏程度的依赖性.在 Re < 1, 三角形, 正方形, 圆形和菱形表明得到的结果, 三角形和二次基板的间距为 14, 94 和109µm, 分别。开放和固体符号代表的实验, 以较少粘性和更高的粘性油分别进行。在 40 < Re < 150 中, 三角形和正方形分别表示三角形和二次基板的实验。黑色、蓝色、红色、绿色和紫色表明, 分别用玻璃、钢、氧化铝、聚苯乙烯磺酸盐和有机玻璃进行了实验。在 Agudo et al (2012)38中, 重新发布 < 1 中的数据将被复制。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57238/57238fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>

Watch this Scientific Journal Video about Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions at JoVE.com

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

提出了两种不同的方法来表征单个珠的初始粒子运动, 即从层流到湍流的沉积床几何函数。

从层流到湍流条件下的规则基底表面初始粒子运动的可视化表征

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to ...

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Equilibrium of a Particle

Open Channel Flow

Application of Newton's Laws of Motion

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8.6K 次观看.  University of Erlangen-Nuremberg. 提出了两种不同的方法来表征单个珠的初始粒子运动, 即从层流到湍流的沉积床几何函数。

视频: Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

制造，操作和表面声波驱动声逆流微流体流动可视化

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

科研

工程学

High-speed Particle Image Velocimetry Near Surfaces

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The complex nature of these flows may be studied using particle image velocimetry (PIV), a laser-based imaging technique for optically accessible flows. Though many forms of PIV exist that extend the technique beyond the original planar two-component velocity measurement capabilities, the basic PIV system consists of a light source (laser), a camera, tracer particles, and analysis algorithms. The imaging and recording parameters, the light source, and the algorithms are adjusted to optimize the recording for the flow of interest and obtain valid velocity data. 
Common PIV investigations measure two-component velocities in a plane at a few frames per second. However, recent developments in instrumentation have facilitated high-frame rate (&gt; 1 kHz) measurements capable of resolving transient flows with high temporal resolution. Therefore, high-frame rate measurements have enabled investigations on the evolution of the structure and dynamics of highly transient flows. These investigations play a critical role in understanding the fundamental physics of complex flows.
A detailed description for performing high-resolution, high-speed planar PIV to study a transient flow near the surface of a flat plate is presented here. Details for adjusting the parameter constraints such as image and recording properties, the laser sheet properties, and processing algorithms to adapt PIV for any flow of interest are included.

A procedure for studying transient flows near boundaries using high-resolution, high-speed particle image velocimetry (PIV) is described here. PIV is a non-intrusive measurement technique applicable to any optically accessible flow by optimizing several parameter constraints such as the image and recording properties, the laser sheet properties, and analysis algorithms.

表面附近的高速粒子图像测速

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The ...

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

密闭静态和流动胶体聚合物混合物的共聚焦成像

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

化学

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

快速成像技术来研究非牛顿流体的跌落冲击动力学

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

高速喷液嵌塞对移动表面的可视化

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

Image-based Lagrangian Particle Tracking in Bed-load Experiments

Image analysis has been increasingly used for the measurement of river flows due to its capabilities to furnish detailed quantitative depictions at a relatively low cost. This manuscript describes an application of particle tracking velocimetry (PTV) to a bed-load experiment with lightweight sediment. The key characteristics of the investigated sediment transport conditions were the presence of a covered flow and of a fixed rough bed above which particles were released in limited number at the flume inlet. Under the applied flow conditions, the motion of the individual bed-load particles was intermittent, with alternating movement and stillness terms. The flow pattern was preliminarily characterized by acoustic measurements of vertical profiles of the stream-wise velocity. During process visualization, a large field of view was obtained using two action-cameras placed at different locations along the flume. The experimental protocol is described in terms of channel calibration, experiment realization, image pre-processing, automatic particle tracking, and post-processing of particle track data from the two cameras. The presented proof-of-concept results include probability distributions of the particle hop length and duration. The achievements of this work are compared to those of existing literature to demonstrate the validity of the protocol.

The manuscript presents a protocol for the conduction of bed-load sediment transport experiments where the moving particles are tracked by image analysis. The experimental facility, the procedures for run realization and data processing, and finally some proof-of-concept results are presented here.

基于图像的拉格朗日粒子跟踪在床载荷实验

Image analysis has been increasingly used for the measurement of river flows due to its capabilities to furnish detailed quantitative depictions at a ...

环境科学

Three-dimensional Particle Tracking Velocimetry for Turbulence Applications: Case of a Jet Flow

3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a set of particles in three dimensions using stereoscopic recording of image sequences. The basic components, features, constraints and optimization tips of a 3D-PTV topology consisting of a high-speed camera with a four-view splitter are described and discussed in this article. The technique is applied to the intermediate flow field (5 &#60;x/d &#60;25) of a circular jet at Re &#8776; 7,000. Lagrangian flow features and turbulence quantities in an Eulerian frame are estimated around ten diameters downstream of the jet origin and at various radial distances from the jet core. Lagrangian properties include trajectory, velocity and acceleration of selected particles as well as curvature of the flow path, which are obtained from the Frenet-Serret equation. Estimation of the 3D velocity and turbulence fields around the jet core axis at a cross-plane located at ten diameters downstream of the jet is compared with literature, and the power spectrum of the large-scale streamwise velocity motions is obtained at various radial distances from the jet core.

A three-dimensional particle tracking velocimetry (3D-PTV) system based on a high-speed camera with a four-view splitter is described here. The technique is applied to a jet flow from a circular pipe in the vicinity of ten diameters downstream at Reynolds number Re &#8776; 7,000.

湍流应用三维粒子跟踪测速:一喷流病例

3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a set of particles in three dimensions using stereoscopic ...

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

一种研究稠密气体和液体分子流体力学过程的模拟宏观技术

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

A protocol to study the contributions of waves to droplet impact dynamics on flowing liquid films is presented.

薄膜控制研究波浪对液滴冲击动力学的影响薄流动液体薄膜

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous ...

Simultaneous Measurement of Turbulence and Particle Kinematics Using Flow Imaging Techniques

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine micro-organisms, and/or sediments in the ocean, or fluidized bed reactors and combustion processes in engineered systems. In order to study the effect of turbulence on the kinematics of particles in such flows, simultaneous measurements of both the flow and particle kinematics are required. Non-intrusive, optical flow measurement techniques for measuring turbulence, or for tracking particles, exist but measuring both simultaneously can be challenging due to interference between the techniques. The method presented herein provides a low cost and relatively simple method to make simultaneous measurements of the flow and particle kinematics. A cross section of the flow is measured using a particle image velocimetry (PIV) technique, which provides two components of velocity in the measurement plane. This technique utilizes a pulsed-laser for illumination of the seeded flow field that is imaged by a digital camera. The particle kinematics are simultaneously imaged using a light emitting diode (LED) line light that illuminates a planar cross section of the flow that overlaps with the PIV field-of-view (FOV). The line light is of low enough power that it does not affect the PIV measurements, but powerful enough to illuminate the larger particles of interest imaged using the high-speed camera. High-speed images that contain the laser pulses from the PIV technique are easily filtered by examining the summed intensity level of each high-speed image. By making the frame rate of the high-speed camera incommensurate with that of the PIV camera frame rate, the number of contaminated frames in the high-speed time series can be minimized. The technique is suitable for mean flows that are predominantly two-dimensional, contain particles that are at least 5 times the mean diameter of the PIV seeding tracers, and are low in concentration.

The technique described herein offers a low cost and relatively simple method to simultaneously measure particle kinematics and turbulence in flows with low particle concentrations. The turbulence is measured using particle image velocimetry (PIV), and particle kinematics are calculated from images obtained with a high-speed camera in an overlapping field-of-view.

流成像技术同时测量湍流和粒子运动学

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine ...