Name: visualization of high speed liquid jet impaction on a moving surface
Uploaded: 2015-04-17T14:00:00.000+00:00
Duration: 8 min 34 s
Description: Watch this Scientific Journal Video about Visualization of High Speed Liquid Jet Impaction on a Moving Surface at JoVE.com

自然科学和加拿大（NSERC）和LB福斯特铁技术，公司的工程研究理事会共同支持这项研究通过NSERC协作研究及发展资助计划。

1.纺纱磁盘设备<ol><li>识别所需的测试条件和记录测试条件在表中（ 例如，环境温度，流体特性，喷射和表面速度， 等等 ）。 </li><li>材料的制备<ol><li>准备甘油水或PEO-甘油水溶液的撞击测试。 <ol><li>在PEO-甘油 - 水试验的情况下，逐渐溶解得到4.5g的PEO粉末（百万和4000000的粘均分子量）为1495.5克蒸馏水在温和磁力搅拌下在24小时的周期。避免过度搅拌PEO样品，防止机械降解。 </li><li>逐渐加入1.5公斤的USP级甘油在24小时内将水PEO溶液以达到0.15％的PEO浓度和50％的甘油浓度的水溶液。 </li></ol></li><li>在每次测试迷你后RT下的密闭容器分开存放测试液体迈兹蒸发，吸水率从环境空气中和污染。表征和内准备五天喷液体。 </li></ol></li><li>实验性能<ol><li>确保所述旋转盘的空气轴承的空气供给阀打开和压力表读数是在正确的工作范围（60-80 psig）的。清除任何可能妨碍盘运动和旋转磁盘用手在两个方向旋转5检查与磁盘和轴承的任何问题。 </li><li>清洁和安全的压缩气体蓄能封闭测试流体加压。倾3公斤测试液体的入1加仑累加器的流体端口。 </li><li>经由压力调节器连接的累加器中的氮罐的气体端口。累加器的流体端口连接到射流喷嘴。 </li></ol></li><li>设置控制系统和高速成像系统。 <ol><li>启动纺纱盘控制软件和VFD控制软件。位置两台高速摄像机电影35厘米离撞击点和调整高倍率镜头从两个角度捕捉到撞击点。 </li><li>调整150W的光纤光源，以达到均匀照亮背景为最佳的图像质量（ 图1）。功率控制系统在这一点上，以方便相机调整。 </li><li>通过点击"自我检查"按钮，在控制软件，以确保系统按预期执行自检程序。 </li></ol></li><li>执行射流冲击测试<ol><li>设置磁盘速度与VFD的控制软件（500-3000转）所需的值。 </li><li>要执行测试，请点击"测试序列"按钮启动从控制软件自动实验序列。软件会自动确定最佳的参数和坐标系统的每个部件，以相应地执行该测试。 </li><li>保存该所得的冲击测试视频（见，例如，屏幕截图在图2中）。阅读和记录表面的速度，喷嘴背压和温度控制软件。 注:每次测试后，盘的清洗顺序自动运行以冲洗和干燥磁盘表面。清洗过程需要重复，直到所有的测试液残渣已被删除。 注意:虽然水和甘油溶液测试流体可以与清洁序列进行清洗，其他LFMs需要用有机溶剂如丙酮清洗。在这种情况下，将清洁材料的布，而不是直接喷射盘。 </li></ol></li><li>数据分析<ol><li>准备关于每个测试条件（ 例如 ，流体特性，环境温度，表面粗糙度等 ）的含电子表格信息。 </li><li>与电影观看软件打开记录射流冲击图像，播放完整的视频录制，在正常加快并观察飞机撞击的行为。 </li><li>记录撞击行为特征（飞溅/飞溅/沉积; 见图3）准备的电子表格，记录任何不寻常的趋势可能预示并发症的实验装置。 </li><li>保存检测结果和条件，在电子表格中。记录值得注意的发现和异常事件的测试日志（ 如色斑/沉积阈值点，飞溅/沉积过渡， 等 ）。截图保存在必要时。 </li><li>进行图像分析测量和记录数据。 <ol><li>启动屏幕上的像素的测量工具。开撞击图像，并通过测量微尺在图像屏幕上的像素的测量工具（ 图4）校准图像的规模。 </li><li>的兴趣度的尺寸（ 例如 ，薄片扩散宽度，W和薄片滞流点半径R;参见图5）与像素测量吨OOL在那里的喷墨似乎是最稳定的，在制备的电子表格中的视频和记录数据的点。然后采取另一基团的尺寸100帧的测量第一组后，以确认这两个射流和薄片是稳定的。在图表上的情节数据点并完成曲线拟合。 </li></ol></li></ol></li></ol> 2.空气炮设备<ol><li>确定所需的试验条件和准备材料的步骤1.1和1.2步。 </li><li>实验性能<ol><li> POWER UP系统控制软件。 </li><li>将弹进炮筒。移动的止动机构靠近枪管退出测试（ 图6）后，以正确采集弹丸。 </li><li>打开加压建筑物空气管线通向空气罐。加压罐30磅和70磅之间，这取决于所期望的弹丸速度。 30 psi的罐压给了约5弹丸速度米/秒，以及70磅给出约25米/秒的速度。 </li><li>准备该压缩气体封闭累加器，用于试验的流体加压。 <ol><li>倾3公斤试验液体到累加器的流体端口。从蓄能器的气体阀门的液体喷射喷嘴连接管和蓄压器压力设定为高达300psig下。 </li></ol></li><li>将摄像机安装到剪式千斤顶。固定剪式千斤顶到位于旁边的喷射喷嘴的平台。 </li><li>确保高强度光源，以横跨从照相机和扩散片后面的平台。检查照明和摄像机定位使用软件控制接口的摄像机观看功能，以及调整定位作为必要的（ 图7）。 </li><li>戴上耳罩用于保护从空气炮的声音鼓风。 </li><li>解锁大炮控制面板，并按下控制面板上的按钮，报警多次信号实验的开始。 </li><li>命中控制面板按钮的打开的电磁阀连接贮气罐与空气炮筒。 </li><li>之后该设备已被发射以及所述弹丸捕获，通过与清洗液和海绵，以除去残留的测试流体擦拭清洁设备。最后，干燥弹丸的撞击表面。 </li></ol></li><li>通过测量所需的时间的旅行一个固定的（10厘米）的距离弹丸的量测量在所记录的高速视频弹丸的速度。分析数据如在步骤1.5。 </li></ol>

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用于空气炮建立弹丸是由一个轻便，木碱。虽然木材料片略经多次试验，已经发现，更有效地吸收动能比弹丸的材料，如塑料或金属，这往往在冲击止动机构粉碎组成。木弹丸的尺寸被设计为紧密地匹配的钢桶内，从而限制了空气泄漏。胶合板的两层之间固定一个1/8"厚橡胶片附连到抛射体的背面进一步收紧围绕筒的内部的密封。装在射弹的顶部的金属撞击表面被紧固不同粗糙度高度的三个独立的...

这项研究的目的是确定应用LFM（液体摩擦改进剂）的液体射流形式到移动表面，同时实现高程度的传输效率和均匀沉积成果的战略。实现这一目标需要开​​发的影响对移动表面的液体射流冲击因素的全面了解。 该项目由需要提高铁路部门使用的润滑应用技术的效率动机。作为减少燃料消耗和机车的维护成本，摩擦改性剂的薄膜的方法，现在被应用到常规铁路轨道的上轨道表面。最近的研究已经表明，将一种类型的水基LFM对于导轨的顶（TOR），摩擦控制降低能耗水平6％和钢轨和车轮凸缘超过50％的1,2-穿通过。其他的研究表明，采用LFM到铁轨减少s横向力和噪音水平，以及，更重要的是，轨道波纹和滚动接触疲劳，这是出轨3,4的一个主要原因的损害。这些结果进一步证实了在东京地铁系统的5场测试。 LFMs目前从连接到几十个机车在整个加拿大和美国的鼓风雾化器分配。在这种形式应用中，线性调频由雾化器安装下方移动轨道车施加到铁轨的顶部。 LFM应用这个模式是难以实施的许多铁路机车，因为所需的高容量和高压空气供给水平可能无法实现。气喷喷嘴也被认为当在侧风操作产生高度不规则的轨道覆盖范围，侧风造成细小雾滴从原来的轨迹偏离。侧风也已知在喷嘴结垢受到牵连，可能对于相同的原因。由于与鼓风雾化器相关的问题，铁路部门目前正在寻找替代办法LFM应用到铁轨。一个可行的解决方案涉及配药LFM通过连续（未雾化）液体喷射的手段，因为液体射流是侧风的影响较不敏感，由于其较低的拖动以惯性比。此外，由于需要的雾化喷嘴的高气压和音量级别不需要在液体射流喷射技术，后者充当维持有效控制LFM应用率更精简和强大的喷涂机制。 类似物理，液滴撞击的区域，已被广泛研究。我们发现通过几个研究者，对于在移动干光滑表面的液滴撞击，溅行为取决于许多参数，包括粘度，密度，表面张力和冲击速度14,15的正常组成部分。鸟<e米&gt;等人证明，无论是正常和切向速度是至关重要16。范围等人和克鲁克斯等人已经表明，用于在静止的干表面的液滴撞击，表面粗糙度显著降低飞溅的阈值（ 即 ，它使液滴更容易产生飞溅）17,18。 尽管它的实际意义，对移动表面射流冲击很少受到关注的学术文献。照韦伯斯特和利斯特进行了大量的实验证明对移动表面检查稳定和不稳定粘性射流冲击和作者开发了一款型号为源源不断的情况下6。 HLOD 等建模的附加 ​​积分条件下通过对未知长度的域三阶的ODE的装置的流动和进行比较的预测配置，与实验结果7。然而，雷诺数审查在这两个研究中比用典型的铁路LFM应用相关联的要低得多。 Gradeck 等数值和实验研究水射流冲击的流场到下各种喷射速度，表面速度，和喷嘴直径条件8移动基板。 Fujimoto 等人的圆形水射流撞击到覆盖的水9的薄膜移动基板的另外研究了流动特性。然而，这两个项目中使用相对较大的喷嘴直径和下表面并与那些在目前的工作中使用的射流速度。而且，尽管前面的实验，数值，和分析研究提供了大量数据中，多数都集中在传热参数，而不是在液体流动过程，如喷溅行为。在本研究中提供的实验方法，从而有助于通过重新液体喷射的应用技术澄清涉及较小喷嘴直径和高速喷射和表面速度条件下这样的技术。本方法也提炼与移动接触线相关的基本流体力学问题的认识。 上述的研究已经通常涉及用低速移动表面低速射流的相互作用。已经有层流高速射流冲击相对较少的研究到高速移动的表面。在高速液体喷射嵌塞射流液体径向地散布在冲击地点的附近，形成了薄的薄片。此薄片然后通过下游的粘性强迫施加的移动表面，产生特征为U形薄片对流。 Keshavarz 等人已报告了实验采用牛顿和弹性液体射流撞击到高速表面。他们分为撞击过程分为两个不同的类型:"沉积＆＃8221;和"飞溅"10。对于撞击到被分类为沉积，喷射液体必须粘附到表面，而飞溅的特征在于液体薄片用于分隔的表面上，并随后分解成液滴。第三个冲击的制度也被形容 - "飞溅"。在此，比较罕见，政权薄片仍然附着在表面，作为"沉积"，但细液滴从靠近薄片的前缘喷出。在随后的非牛顿流体的影响的研究中，Keshavarz 等人的结论是，飞溅/沉积阈主要由雷诺数和Deborah号码确定的，而喷射冲击角度和喷射速度进行表面速度比仅具有较小的影响11 。在根据可变空气压力下进行的实验中，Moulson 等人发现，飞溅/沉积门槛雷诺数显着与降低环境空气压力的增加（ 即 ，较高的环境压力使射流更容易发生飞溅），同时减少环境空气的压力低于某一阈值抑制飞溅完全12。这一发现有力地表明，作用在薄片气动力在使薄片剥离和随后溅起到至关重要的作用。在高速撞击在高速基板最近的工作，斯特林表明，对于基底速度和喷射条件接近溅阈值时，飞溅可能由非常小的局部的表面粗糙度和次要喷射不稳触发。他还表明，在这些条件下的薄片剥离和再附着是一个随机过程13。 这里所描述的实验方案，可以用于研究涉及的流体与运动高速表面的相互作用等物理的情况。例如，相同的方法可以用于研究直升机BLAD电子涡流相互作用（其中，涡旋流体被着色用示踪粒子）和表面的机器人喷涂。

<table><tbody><tr><td colspan="4">Equipment for Air Cannon Set-Up</td></tr><tr><td>30-gallon air tank</td><td>Steel Fab</td><td>A10028</td><td></td></tr><tr><td>Solenoid actuated poppet valve</td><td>Parker Hannifin Corp.</td><td>#16F24C2164A3F4C80</td><td></td></tr><tr><td>1.5&quot; NPT rubber hose</td><td></td><td></td><td></td></tr><tr><td>Rectangular steel tubing</td><td></td><td></td><td></td></tr><tr><td>Stop mechanism</td><td>Customized</td><td></td><td></td></tr><tr><td>Stainless steel plates</td><td>Customized</td><td></td><td></td></tr><tr><td>Wooden projectile</td><td>Customized</td><td></td><td></td></tr><tr><td>1 kW high-intensity incandescent light</td><td>Photographic Analysis Ltd.</td><td>T986851</td><td></td></tr><tr><td>Light diffuser sheet</td><td></td><td></td><td></td></tr><tr><td>Optic sensor</td><td>BANNER</td><td>SM312LV</td><td></td></tr><tr><td colspan="4">Equipment for Spinning Disc Set-Up</td></tr><tr><td>Motor</td><td>WEG</td><td>TEFC-W22</td><td></td></tr><tr><td>Bearings</td><td></td><td></td><td></td></tr><tr><td>Disk</td><td>Customized</td><td></td><td></td></tr><tr><td>Fiber optic light source</td><td>Fiberoptics Technology Incorporated</td><td>MO150AC</td><td></td></tr><tr><td>High intensity LED array</td><td>Torshare Ltd.</td><td>TF10CA</td><td></td></tr><tr><td>Vacuum</td><td>Ridge Tool Company</td><td>WD09450</td><td></td></tr><tr><td>Interrupter</td><td>Customized</td><td></td><td></td></tr><tr><td colspan="4">Shared Equipment for Both Devices</td></tr><tr><td>Phantom v611 high-speed cine camera</td><td>Vision Research Inc.</td><td>V611</td><td></td></tr><tr><td>Phantom v12 high-speed cine camera</td><td>Vision Research Inc.</td><td>V12</td><td></td></tr><tr><td>Zoom 7000 lens</td><td>Navitar Inc.</td><td>Zoom 7000</td><td></td></tr><tr><td>Zoom 6000 lens</td><td>Navitar Inc.</td><td>Zoom 6000</td><td></td></tr><tr><td>Compressed nitrogen tank</td><td>Praxair Technology, Inc.</td><td></td><td></td></tr><tr><td>Pressure regulator</td><td>Praxair Technology, Inc.</td><td>PRS20124351CGA</td><td></td></tr><tr><td>Hose for compressed nitrogen</td><td>Swagelok Company</td><td>SS-CT8SL8SL8-12</td><td></td></tr><tr><td>Hose for liquid</td><td>Swagelok Company</td><td>SS-7R8TA8TA8</td><td></td></tr><tr><td>Accumulator</td><td>Accumulators, Inc.</td><td>A131003XS</td><td></td></tr><tr><td>Solenoid Valve</td><td>Solenoid Solutions Inc.</td><td>2223X-A440-00</td><td></td></tr><tr><td>Pressure transducer</td><td>WIKA Instruments Ltd</td><td>#50398083</td><td></td></tr><tr><td>Nozzle assembly</td><td>Customized</td><td></td><td></td></tr><tr><td>Glycerin</td><td></td><td></td><td></td></tr><tr><td>Poly(ethylene oxide)</td><td></td><td></td><td></td></tr></tbody></table>

visualization of high speed liquid jet impaction on a moving surface

两个装置用于检查液体射流冲击在高速移动表面进行了说明:空气炮装置（用于检查在0至25米/秒的表面速度）和一个旋转盘装置（用于检查在15和100m的表面速度/秒）。空气炮线性横动是旨在加速金属轨道表面安装在一木制弹丸顶部气动能量供电系统。一个增压缸装有一个电磁阀快速释放加压空气进入桶内，迫使弹下来炮筒。弹丸行进的喷雾喷嘴，其撞击液体喷射到它的金属上表面的下方，并且弹丸然后击中一个止动机构。一种照相机记录了射流冲击，以及一个压力传感器记录下喷嘴背压。旋转盘设置由钢盘是通过可变频率驱动（VFD）马达速度达到500至3000转的。喷雾系统SImilar到空气炮产生的液体射流撞击到所述旋转盘，并放置在多个光纤接入点摄像机记录射流冲击。射流冲击过程的录像记录和检查，以确定撞击的结果是否飞溅，飞溅，或沉积。该设备是第一个涉及低雷诺数液体射流在高速移动的表面高速撞击。除了它的铁路行业应用中，所描述的技术可以用于技术和工业用途，如炼钢和可能有关的高速三维打印。

<html>正如在引言部分所讨论的，液体射流冲击相关的三个主要行为是沉积，飞溅和飞溅。这些射流冲击行为是利用记录由位于各种光点高速电影摄像机的视频数据中观察到。静止图像，从视频记录，它描绘三个液体喷射的结果获得的实例示于图3中 。 图3A示出了液体喷射沉积，其中，所述喷射在一个朝向撞击表面完全伸直并源源不断流动。射流附着到表面，并保持在表面?...

Watch this Scientific Journal Video about Visualization of High Speed Liquid Jet Impaction on a Moving Surface at JoVE.com

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

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 ...

visualization-of-high-speed-liquid-jet-impaction-on-a-moving-surface

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11.4K 次观看.  University of British Columbia. 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.

视频: Visualization of High Speed Liquid Jet Impaction on a Moving Surface

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 ...

科研

工程学

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 ...

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 ...

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

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.

Two different methods for characterizing the incipient particle motion of a single bead as a function of the sediment bed geometry from laminar to turbulent flow are presented.

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 ...

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 ...

Impacts of Free-falling Spheres on a Deep Liquid Pool with Altered Fluid and Impactor Surface Conditions

Vertical impacts of spheres on clean water have been the subject of numerous water entry investigations characterizing cavity formation, splash crown ascension and Worthington jet stability. Here, we establish experimental protocols for examining splash dynamics when smooth free-falling spheres of varying wettability, mass, and diameter impact the free surface of a deep liquid pool modified by thin penetrable fabrics and liquid surfactants. Water entry investigations provide accessible, easily assembled and executed experiments for studying complex fluid mechanics. We present herein a tunable protocol for characterizing splash height, flow separation metrics, and impactor kinematics, and representative results which might be acquired if reproducing our approach. The methods are applicable when characteristic splash dimensions remain below approximately 0.5 m. However, this protocol may be adapted for greater impactor release heights and impact velocities, which augurs well for translating results to naval and industry applications.

This protocol demonstrates the basic experimental configuration for water entry experiments with free-falling spheres. Methods for the alteration of liquid surface with penetrable fabrics, the preparation of chemically non-wetting spheres, and steps for splash visualization and data extraction are discussed.

自由落体对变液和冲击物表面条件下深层液池的影响

Vertical impacts of spheres on clean water have been the subject of numerous water entry investigations characterizing cavity formation, splash crown ...

High Throughput Analysis of Liquid Droplet Impacts

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters such as material properties, impact conditions, and experimental configurations. Compounding this, drop impacts are often studied using data-rich high-speed photography, so that it is difficult to analyze many experiments in a detailed and timely manner. The purpose of this method is to enable efficient study of droplet impacts with high-speed photography by using a systematic approach. Equipment is aligned and calibrated to produce videos that can be accurately processed by a custom image processing code. Moreover, the file structure setup and workflow described here ensure efficiency and clear organization of data processing, which is carried out while the researcher is still in the lab. The image processing method extracts the digitized outline of the impacting droplet in each frame of the video, and processed data are stored for further analysis as required. The protocol assumes that a droplet is released vertically under gravity, and impact is recorded by a camera viewing from side-on with the drop illuminated using shadowgraphy. Many similar experiments involving image analysis of high-speed events could be addressed with minor adjustment to the protocol and equipment used.

This protocol enables efficient collection of experimental high-speed images of liquid drop impacts, and speedy analysis of those data in batches. To streamline these processes, the method describes how to calibrate and set up apparatus, generate an appropriate data structure, and deploy an image analysis script.

液滴冲击的高通量分析

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters ...

A Microfluidic System with Surface Patterning for Investigating Cavitation Bubble(s)&#8211;Cell Interaction and the Resultant Bioeffects at the Single-cell Level

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass substrate, that precisely controls the generation of tandem bubbles and individual cells patterned nearby with well-defined locations and shapes. We then demonstrate the generation of tandem bubbles by using two pulsed lasers illuminating a pair of gold dots with a few-microsecond time delay. We visualize the bubble-bubble interaction and jet formation by high-speed imaging and characterize the resultant flow field using particle image velocimetry (PIV). Finally, we present some applications of this technique for single cell analysis, including cell membrane poration with macromolecule uptake, localized membrane deformation determined by the displacements of attached integrin-binding beads, and intracellular calcium response from ratiometric imaging. Our results show that a fast and directional jetting flow is produced by the tandem bubble interaction, which can impose a highly localized shear stress on the surface of a cell grown in close proximity. Furthermore, different bioeffects can be induced by altering the strength of the jetting flow by adjusting the standoff distance from the cell to the tandem bubbles.

A microfluidic chip was fabricated to produce pairs of gold dots for tandem bubble generation and fibronectin-coated islands for single-cell patterning nearby. The resultant flow field was characterized by particle image velocimetry and was employed to study various bioeffects, including cell membrane poration, membrane deformation, and intracellular calcium response.

用的表面图案化微流体系统用于在单细胞水平调查空泡（S） - 细胞的相互作用及产生的生物效应

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass ...

生物工程

Visualization of Flow Past a Bluff Body

Source: Ricardo Mejia-Alvarez, Hussam Hikmat Jabbar and Mahmoud N. Abdullatif, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Owing to the non-linear nature of its governing laws, fluid motion induces complicated flow patterns. Understanding the nature of these patterns has been the subject of intense scrutiny for centuries. Although personal computers and supercomputers are extensively used to deduce fluid flow patterns, their capabilities are still insufficient to determine the exact flow behavior for complex geometries or highly inertial flows (e.g. when momentum dominates over viscous resistance). With this in mind, a multitude of experimental techniques to make flow patterns evident have been developed that can reach flow regimes and geometries inaccessible to theoretical and computational tools.
This demonstration will investigate fluid flow around a bluff body. A bluff body is an object that, due to its shape, causes separated flow over most of its surface. This is in contrast to a streamlined body, like an airfoil, which is aligned in the stream and causes less flow separation. The purpose of this study is to use hydrogen bubbles as a method of visualizing flow patterns. The hydrogen bubbles are produced via electrolysis using a DC power source by submerging its electrodes in the water. Hydrogen bubbles are formed in the negative electrode, which needs to be a very fine wire to ensure that the bubbles remain small and track fluid motion more effectively. This method is suitable for steady and unsteady laminar flows, and is based on the basic flow lines that describe the nature of the flow around objects. [1-3]
This paper focuses on describing the implementation of the technique, including details about the equipment and its installation. Then, the technique is used to demonstrate the use of two of the basics flow lines to characterize the flow around a circular cylinder. These flow lines are used to estimate some important flow parameters like flow velocity and the Reynolds number, and to determine flow patterns.

Flow Around a Bluff Body, Bubbles and Von Karman Vortex Street

通过钝体流的可视化

Source: Ricardo Mejia-Alvarez, Hussam Hikmat Jabbar and Mahmoud N. Abdullatif, Department of Mechanical Engineering, Michigan State University, East ...

教育

JoVE Science Education

机械工程

Jet Impinging on an Inclined Plate

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The goal of this experiment is to demonstrate how a fluid flow exerts forces on structures by conversion of dynamic pressure into static pressure. To this end, we will make a plane jet impinge on a flat plate and will measure the resulting pressure distribution along the plate. The resultant force will be estimated by integrating the product between the pressure distribution and appropriately defined area differentials along the surface of the plate. This experiment will be repeated for two angles of inclination of the plate with respect to the direction of the jet and two flow rates. Each configuration produces a different pressure distribution along the plate, which is the result of different levels of conversion of dynamic pressure into static pressure at the plate's surface.
For this experiment, pressure will be measured with a diaphragm pressure transducer connected to a scanning valve. The plate itself has small perforations called pressure taps that connect to the scanning valve through hoses. The scanning valve sends the pressure from these taps to the pressure transducer one at a time. The pressure induces mechanical deflection on the diaphragm that the pressure transducer converts into voltage. This voltage is proportional to the pressure difference between the two sides of the diaphragm.

Jet Impinging and Conversion of Dynamic Pressure into Static Pressure

射流撞击斜面板

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The goal of this ...