这种材料是基于工作由美国国家科学基金会的支持下批准号CBET-1032930大学的密歇根州的定量激光诊断实验室进行工作。

1。实验室安全<ol><li>回顾激光安全操作前的激光材料，并确保培训的要求已得到满足。 </li><li>获取正确的安全设备与激光器工作。每一个人都应该穿一双激光防护镜，将阻止激光的发射波长（次）。在实验室之外进行安装警告标志，让别人知道激光器工作时。恒光学平台周围的激光安全布隔离从其他同事在一个共享的空间实验室。 </li><li>删除所有的手表和珠宝，工作时用激光。 </li><li>考虑光束路径时，设立设备：设置装备进行调整，以便将不需​​要达到梁的上方或下方。 </li><li>阅读激光手册，以确定如何安全地操作激光。 </li><li>你的眼睛保持水平的激光束的飞机！ </li></ol> 2。台式设置<ol><li>确定的放大倍率t帽子将所需的应用程序，并选择合适的镜头。的放大倍数（M）除以芯片的摄像头的视场的视场（FOV）的相应长度的长度可被确定。在这个例子中，摄像头芯片的长度是17.6毫米，视场的相应长度为2.4mm。因此，M = 17.6毫米/ 2.4毫米= 7.33。这里使用的是长途显微镜来实现这一较小的FOV。 <ol><li>预期的速度在近壁区进行一些粗略的计算。使用这些估计值，以确定记录的参数，例如，帧速率和延迟时间根据实际指引的PIV 1,2。确定的时间才能够把一个粒子前往8个像素。这将决定（dt）的每一个激光脉冲之间的时间延迟。按时间序列的PIV 1/dt将确定必要的摄像机的帧速率，必须是小于相机所允许的最大帧速率。小调整这些参数可能购买要优化的流记录，获得高品质的速度数据。如果所需要的帧速率超过最大激光重复率，也可以使用两个激光器执行PIV横跨在帧模式。在这个例子中，帧速率（5千赫）不超过最大重复率的激光，因此只有一个单一的激光需要执行PIV在时间序列模式。 </li></ol></li><li>激光级表<ol><li>激光头设置在一个电平的光表的一端。将直接在光束路径表在其另一端的光束转储。 </li><li>将激光头的光轨之间的光束转储。磁带目标光束阻滞剂，固定梁阻滞剂给承运人，将在轨道上的载体。 </li><li>一个低电流设定设定了激光器的电流 - 足以产生激光，但没有足够的燃烧一张纸。打开激光来回滑动托盘。进行小的调整激光位置UNT金正日的激光束的中心保持在一个地方，为载体来回移动。修复激光光学表。 </li><li>测量使用的组合正方形的激光束的中心的高度。关闭激光。 </li></ol></li><li>安装激光板料成形光学<ol><li>取出导轨，但这里的光束阻断剂与目标前面的光束转储。打开激光，并仔细标记的中心的光束击中目标。将片材成型的光学元件，这是光束均化器（BH），还包括一个片材形成望远镜在此演示中，在激光光路形成激光片。激光片材的高度必须大于视场。 BH中心目标上的标记的高度和宽度的激光负债表调整位置，并保持背反射到激光腔旅行回来。将光圈之间的激光头和BH，如果有必要，以避免反射。关闭激光。升在这个示范的飞行片的高度分别为8毫米和0.5毫米的厚度，脉冲能量为0.4兆焦耳/脉冲。 </li><li>如果空间有限，在光学平台上，放置90°45°高反射镜将激光片。磁带的另一个目标光束阻断剂，修复束阻滞剂给承运人，放在载体上轨。将轨组装后镜。打开激光。镜进行小的调整，直到光片中心目标停留在一个地方，因为它沿轨道滑动。 </li><li>设定了激光器的重复率，以匹配测量（在这里所讨论的例子中的5千赫）的帧速率，并设定了激光器的电流的最大设定值。把BH和目标之间的铁路。将第二束阻滞剂载体，将在轨道上组装。打开激光。来回滑动托盘从BH的焦点，以确定位置。 FOC的位置标记人点相对的BH。如果使用反射镜时，使测量相对的反射镜。测量高度的近似激光片的焦点。关闭激光。 </li></ol></li><li>安装并调节长距离显微镜和相机<ol><li>标记长途显微镜（LDM）和摄像头孔，使用一个中心广场和联合广场的水平和垂直中心线。测量表和LDM和相机的水平中心线之间的距离。 </li><li>修复LDM和相机的载流子，和使用任何隔离物，如垫圈或螺母，使LDM和相机的水平中心线是在同一高度上。修复LDM和相机在轨道上。将LDM和相机使用相应的适配器。调整组件的高度，使水平中心线光片为中心的表中的相同的距离，。 </li><li>修正了一个翻译阶段的焦点在前面的标志INT的光束。翻译阶段的运动将是平行的光束传播。翻译阶段的相机组件的轨道与固定，从而使整个组件垂直于光片。中心相机组件LDM和相机的焦点对准垂直中心线。 </li><li>将相机连接到计算机和高速控制器（HSC）。将HSC的激光。保持的摄像头安装在帽和校准的的PIV软件程序（，LaVision戴维斯7.2）在执行力度。 </li><li>在软件程序中，将相机设置为连续抢模式和摄像头组件取下帽子。将结合广场的焦点。沿导轨移动相机和LDM的标尺，成为关注的焦点，直到清晰的图像。继续沿导轨移动相机和LDM，并把图片转换成焦点LDM的调焦杆，直到摄像头芯片跨越所需的字段的视图（2。4×1.8毫米2对应的800×600像素芯片）。 </li></ol></li><li>板固定到支架上，因此，它是平行于表，并将其放置在焦点。提高板，以便它在计算机上的图像是可见的。关闭连续抓帽的相机组件。打开激光和确保激光片沿板的表面接触。 </li></ol> 3。流量设置<ol><li>在这个演示中，PIV进行录制图像硅油液滴散射光。油滴中创建使用油雾化器。下列项目连接气源：微粒过滤器，油过滤器，压力调节阀，质量流量计，油雾化。将雾化器的输出连接到钢管。使用坐骑和夹紧钢管固定在光学平台，提升管上面的表，并直接向板。 </li><li>打开供气阀。设置回&gt; 140千帕创建足够的流过系统的压力调节器的压力。 </li><li>开启的流量和雾化喷射和雾化器的旁通阀通过调整播种密度。 </li></ol> 4。优化设置<ol><li>在软件程序中输入的帧速率。检查的HSC发送触发信号的帧速率相匹配的激光。上的激光电源，设置重复率和电流（5 kHz和15.5 A在这个例子中，分别）。设定了激光器的外部模式。激光组对激光的重复率相匹配，然后切换到外部模式，否则激光将过热的HSC必须不断收到触发信号。 </li><li>设置相机不断抢，打开激光，开启雾化器。对LDM使用聚焦杆，以确保颗粒图像处于焦点。另外，还要确保粒子图像的强度是不饱和凸轮时代。如果是这样的话，掉头向下的激光电流 - 这会影响焦点位置！重复步骤2.3.3和2.4.3中，如果激光电流改变。关闭抓重点粒子图像模式时实现。 </li><li>获得有效的速度数据的记录，审查和调整参数<ol><li>记录几百流的图像。录制结束后，检查记录的图像，以确保颗粒不超过8个像素转移，播种密度为8-10颗粒每32×32像素的审讯窗口的顺序，并验证图像的焦点。重复步骤4.3.1-4.3.4直到已经达到上述标准。 </li><li>如果颗粒被转移超过8个像素，减小两者之间的PIV激光脉冲dt的，以取得最大的8个像素的位移。如果颗粒转移基本上小于8个象素，dt的增加。对于单激光PIV系统，dt的调整通过改变帧速率，因此激光的重复率。使用两个激光器的PIV，dt是从所述第一激光和第二激光的一个脉冲的脉冲之间的时间延迟。如果调整DT的问题并没有缓解，帧速率和激光重复率可能会首先进行调整，然后DT可能需要再次进行微调。 </li><li>如果是难以跟踪整个一系列的图像中的颗粒组，可能有太多的平面运动。有几种方法来解决这个问题：1）从焦点偏移的相机组件，使相机的成像较厚的轻质板材，相机之间的工作距离和光板面组件（二）增加和集中使用对焦杆），以实现更大范围内的深度的焦点，但是，这将降低的空间分辨率。 </li><li>如果播种密度过于稀疏或过于密集，增加或减少雾化喷嘴的数量。 </li></ol></li></ol> 5。运行实验<ol><li>执行CAMER“一个强度上限设置在相机上装配强度的参考校准。一旦校准完成后，取下帽子。 </li><li>设置激光优化的重复率和电流。激光切换到外部模式之前，请确保激光接收连续触发信号相匹配的设定频率。打开激光。 </li><li>记录光片放牧板面上的一个序列的背景图像。保存这些图像。 </li><li>打开的流动，并允许以稳定的流量。 </li><li>将相机设定为连续抢确认摄像头收集集中粒子图像。关闭连续抢模式。 </li><li>输入所需数量的图像，然后按记录。 </li><li>一旦录制完成，关闭流和激光。检查图像序列的检查粒子移位，播种密度和粒子图像的焦点。保存记录，如果满意，否则重复步骤5.4-5.7。 </LI&gt; <li>重复步骤5.4-5.7收集更多的运行。 </li><li>增加曝光时间（相机采集图像的每帧的时间量）的摄像头。 </li><li>轻质板材平面设置校准目标，并确保它与板接触。从后面用一个光源（ 即手电筒）照射目标。随着连续抢模式的相机，调整目标，使所记录的图像中的重点和不失真。确保板之间的接触点和目标图像中是可见的 - 用于确定在影像中的板的位置，这一点是至关重要的。 </li><li>记录10张图像校准目标。重复步骤5.9-5.11每次相机组件或改变焦点。 </li></ol> 6。数据处理<ol><li>本演示中使用的PIV软件程序LaVision戴维斯8.1。平均每套校准目标图像。使用生成的图像校准柔齿确定真实世界中采集的图像尺寸。 </li><li>每个校准应用到对应的一组图像。 </li><li>确定校正后的图像中的板的位置。这个信息是必要的，用于创建一个的几何蒙板（6.6）。 </li><li>平均的背景图像。确定，如果从表面激光反射显著贡献的背景噪声强度计数的平均背景图像进行比较，播种颗粒计数的强度。附近的墙上有明亮的激光反射强度高于粒子强度。这将产生不利影响的的PIV相关性壁附近的和限制的位置的第一个可靠的向量最近的在墙壁上。在这个例子中，激光反射没有显着贡献的背景。 </li><li>前处理校准流量图像使用一个高通滤波器（减去滑动背​​景过滤器），以除去大强度波动蒸发散的背景下，如激光反射。粒子信号强度小的波动，并通过过滤器。 </li><li>定义几何蒙板 - 使用矩形遮罩板位于images禁用矢量计算。注：戴维斯有两个选项为几何的面具：PIV的相关性，使指定区域内和禁用PIV指定区域内的相关性。本演示中使用面具指定区域内启用的PIV算法。 </li><li>在“高级掩码设置”菜单，确保面具适当应用（ 即只使用面罩内的像素）。 </li><li>指定向量计算过程：在这个例子中，一个多道程序的窗口大小减小 - 2初始通行证50％使用64 x 64像素的审讯窗口重叠随后3次传球，50％重叠使用32×32像素的审讯窗口。 </li><li>速度矢量字段在此演示后处理使用五个子程序以提高质量互相关的结果：a）使面罩永久; b）拆下载体的峰值比（Q）&lt;1.1;三）应用中值滤波;）删除组&lt;5向量ê）应用矢量填充。该峰值比（Q）被定义为<img alt="方程" fo:src="/files/ftp_upload/50559/50559eq1highres.jpg" src="/files/ftp_upload/50559/50559eq1.jpg" /> ，其中P1和P2是第一和第二相关峰值最高，分别和最小的相关平面中的最小值。Q是用于评估一个向量的质量度量。 Q性最高的相关峰值，这会导致在最好的载体，共同表示由第二最高相关峰值的相关背景。与Q接近1的载体是一个迹象表明，相关性最高的峰值是一个虚假的峰值。接下来，中值滤波确定中位数矢量（U，V 中位数中位数一组向量和相邻向量的偏差（U，V RMS有效值 ））。中值滤波拒绝中间载体（U，V），如果它不符合下列条件：U 位数 - U RMS≤U≤U位数 + U RMS和V 中位数 - V RMS≤V≤V中位数 + V RMS。此外，它是未能取得杂散载体组中指定的速度矢量计算，如果一个大的重叠。因此，它是可以除去用小于指定数目的向量的向量组。一旦被删除，杂散载体矢量填充，也可以使用与确定非零相邻向量的内插向量，填补了空白。最后，应用口罩永久删除任何载体外面罩。 </li><li>评估结果的质量：a）你的结果物理意义？ （ 即较慢的速度的边界附近，从墙上的距离的增加而上升的速度向量的方向跟随的流量等 ）的一般方向，二）主要是由第一选择矢量得到的矢量场（由PIV处理软件）。通常情况下，建议第一选择矢量的分数是高于95％的。一个更广泛的范围后处理步骤中描述的文献， 如 1,2。 </li></ol>

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L., Sick, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+imaging+analysis+of+misfires+in+a+spray-guided+direct+injection+engine.">High-speed imaging analysis of misfires in a spray-guided direct injection engine.</a> Proceedings of the Combustion Institute. 33 (2), 3089-3096 (2011).</li></ol>

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任何光学流量测量技术，高速粒子图像测速（PIV）的设置规划，需要评估的约束和评估的测量任务的最佳妥协。依赖于的流所研究的详细信息的选择的图像的放大倍率，帧速率，激光表属性，和分析算法。如果需要的话，必须进行勘探测量，识别参数设置高保真测量。 本文介绍的一般程序和一些示例结果高速PIV研究边界层流沿平板。 500幅图像的序列被记录在5 kHz。长途显微镜下，实现了2.4×1.8毫米2场的视图位于板面。种子油滴实现了与高品质的照明光束从一个脉冲二极管泵浦固态激光器，被扩大成光的sh余氏使用的光束均化器。光束均化器包含一个微透镜阵列由小柱面透镜和一个额外的，集成的望远镜。微透镜阵列由入射光束分裂成小束在垂直方向上扩展的圆形光束。然后下面的望远镜叠加小束创建一个光片​​正常光束传播的光板面均匀的光强度分布。图像处理使用PIV互相关算法。应当指出的是形成均匀的光束有所帮助，特别是当工作表面附近，但它不是在这里描述的应用程序的关键。 在此过程中介绍的方法使非侵入式的高清晰度，高速的流量使用健壮的相关算法的调查。这种高清晰度，高速测量技术的主要优点是高时空分辨率，识别和跟踪的能力结构的演变，内流。使用这些技术，Alharbi 6和：Jainski， 等 。8表现出的能力的内燃机的边界层内的可视化和跟踪涡结构。这些关键特性使调查的高瞬变流的结构和动力学。此外，PIV可能会扩展至二维（2D-2C）成分速度场（这里描述的）解决3组件（3C）（立体声-PIV），在一个平面上，并在一个卷（断层PIV扫描，全息PIV PIV）。此外，PIV和其它技术，如平面激光诱导荧光（PLIF），过滤瑞利散射（FRS），和热成像的荧光体，以实现同步的二维测量的速度和其他标量（温度，组分浓度，当量比）11可以被实现-14。在这些光学，激光为基础的方法，可直接应用于调查质量和能量交换过程的许多应用中，如近壁流动的内燃机。

多维测量的速度和流场的时间能够跟踪在许多领域的科学，工程科学和医学等提供重要信息。当中使用最广泛的血流成像技术，粒子图像测速（PIV）。最初成立为平面的技术测得的快照的两个平面的速度分量，PIV变种已开发，以提供三分量和体积的测量能力。所有PIV系统中的示踪粒子，在一个或多个光源，一个或多个摄像机组成。固体颗粒或液滴常用作为示踪粒子，但也可以用来作为示踪粒子流中的固有的气泡。相机（次），然后散射或发射的光由光源（次）照射后从示踪粒子的图像（S）。变化1,2之间的范围广泛的最常见的一种捕获两个大鼠在一个平面上的速度分量E几帧每秒。最近，已启用新的仪器高帧速率的测量（1千赫）按照流量在kHz范围内的湍流时间尺度。 PIV确定通过跟踪从一对被分离的图像，由一个已知​​的时间延迟的颗粒群的平均运动速度场。每个图像被划分成网格的间隔规则的询问窗口。最常见的询问窗口的大小是32×32像素。的算法计算出的互相关函数的所有询问窗口，导致每个询问窗口的一​​个位移矢量，并因此产生一个规则的网格的向量。除以位移矢量场的时间延迟，然后确定速度矢量场。 规划PIV测量时，重要的是要意识到，通常的选择实验的设置是相互冲突的要求之间的一种折衷。换句话说，实验精神状况需要仔细计划捕捉流动方面的重要性，学习手。这些书由拉费尔等1和阿德里安和Westerweel 2提供优异的深入讨论这些约束。下面我们着重介绍几种，在目前情况下是最关键的。 领域的视角（FOV）的选择将设置参数选择的起点。摄像头芯片上的像素的数量，然后确定的空间分辨率得到的向量的数目，假设一个人选择使用询问窗口大小为32×32像素，通常具有50％的重叠期间的互相关程序。 8-10每审讯窗口颗粒播种密度一般是需要帮助的互相关函数。不过，也有特殊的算法，如粒子跟踪测速（PTV）和时间平均相关办法，可能可用于解决接种密度低的情况下，（1-3颗粒/询问窗口）的情况一样，与附近的表面成像。请注意，每个审讯窗口内的速度梯度应该是很少的，以避免偏见产生的代表载体，窗口。 一个既定的规则进行的拇指的是，在第一和第二帧的粒子之间的位移应不超过8个像素（¼的审讯窗口的大小），以减少数量的配对损失（损失的粒子图像的询问窗口内从所述第一帧的第二帧）的相关性。其结果是，（dt）的两个连续的激光脉冲之间的时间作相应的调整。然而，下方的相当于8像素位移的减少dt的降低速度的动态范围，因为下端的分辨率极限是0.1像素的位移的顺序。 类似的8像素的位移瓦特内成象平面，最高速度的颗粒不应遍历超过¼光片厚度，再次，以减少损失的配对。由于两个激光脉冲之间的时间延迟用于光片平面内，以确保最佳的相关性，在片材的厚度是在此上下文中的变量。虽然不是至关重要的，因为它是基于强度的测量，如平面激光诱导荧光成像如图3所示 ，顶帽附近的光束轮廓的光强度的均匀性，特别是对较高分辨率的成像帮助PIV质量。 在一般情况下，可以使用的流动的性质，所研究的一些假设为出发点，在选择的实验参数。然后，探索性实验，可能需要细化的设置。 在这里，我们描述了如何建立一个允许高帧频成像测量两种速度组件管理的PIV实验NTS空间分辨率，是足以解决边界层结构。这是通过使用高重复率TEM 00二极管泵浦固态激光器，长途显微镜，以及高帧速率的CMOS摄像头。成像表面附近的一些细节也包括在内。

<table border="1" fo:keep-together.within-page="always">
	<tbody>
		<tr>
			<td>Name of Equipment</td>
			<td>Company</td>
			<td>Model</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>High-speed 532 nm Nd:YAG laser</td>
			<td>Quantronix</td>
			<td>Model: Hawk I</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Long distance microscope (QM-100)</td>
			<td>Questar</td>
			<td>Model: QM-100</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>High-speed CMOS camera (Phantom v7.3)</td>
			<td>Vision Research</td>
			<td>Model: Phantom v7.3</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Atomizer (TSI 9306)</td>
			<td>TSI</td>
			<td>Model: 9306</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Silicone oil</td>
			<td>Dow Corning CST 510</td>
			<td>CST 510 Fluid</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Beam homogenizer</td>
			<td>Fraunhofer</td>
			<td>&nbsp;</td>
			<td>Custom made part</td>
		</tr>
		<tr>
			<td>45&deg; high-reflectivity (HR) 532 nm turning mirror</td>
			<td>Laser Optik</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
		<tr>
			<td>Aperture</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
		<tr>
			<td>Calibration target</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Custom made part</td>
		</tr>
		<tr>
			<td>PIV recording and processing software</td>
			<td>LaVision</td>
			<td>Software: Da Vis</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>High-speed controller (HSC)</td>
			<td>LaVision</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Optical rail and carriers</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
		<tr>
			<td>Laser beam blocks and traps</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
		<tr>
			<td>Mounts for optical elements</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
		<tr>
			<td>Translation stage</td>
			<td>Newport</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Metal tubing to create jet flow</td>
			<td>McMaster-Carr</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
		<tr>
			<td>Combination square and centering square</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Multiple suppliers</td>
		</tr>
	</tbody>
</table>

high-speed particle image velocimetry near surfaces

多维和瞬变流在科学，工程和健康科学的许多领域发挥关键作用，但往往不能很好地理解。利用粒子图像测速（PIV），一种基于激光成像技术，光学访问流量，这些流量可以研究的复杂性。虽然许多形式的PIV存在延伸超越了原来的平面状的双组分的速度测量功能的技术，基本的PIV系统包括光源（激光），一个摄像头，示踪粒子，和分析算法。成像和记录参数，光源，该算法被调整，以优化的还流的记录，并获得有效的速度数据。 常见的PIV调查测量双组分速度在每秒几帧的在一个平面上。然而，最近的仪器仪表的发展提供了便利的高帧速率（&gt; 1千赫）测量能够解决过渡耳鼻喉科流量高时间分辨率。因此，高帧速率测量的结构和动力学演化的高瞬变流功能的调查。这些调查中发挥了关键作用在理解复杂流动的基本物理。 这里介绍的详细描述进行高分辨率，高速平面PIV研究平板表面附近的瞬时流量。调整参数限制，如图像和录制属性，激光片属性，以及处理算法，以适应PIV利益流的详细信息都包括在内。

照片的设置如图1所示。 图2中所示的32×32像素的询问窗口从两个连续捕获的图像的壁附近的上游的粒子图像。在图2a中的粒子位移2-3个像素，在图2b中的权利和满足“四分之一规则”，其中规定，在面内和平面外的粒子位移不应超过¼询问窗口大小。此外，粒子密度每审讯窗口应该是大约8-10颗粒，，因为PIV相关算法跟踪颗粒组。然而，在近壁PIV调查接种密度通常是1-3颗粒的顺序。因此，应使用特殊的算法来解决与播种密度较低，如粒子跟踪测速（PTV）算法跟踪单个粒子1,2,4-6研究。时间平均相关办法，7,8也可以被用来接种密度低的问题，但是这通常会导致时间分辨率的损失。此外，靠近墙壁的影响，可能产生不利影响的PIV相关性和产生虚假的载体明亮的激光反射成像。这些明亮的反射也限制在墙上的法线方向的速度矢量的第一个有效的位置。前处理的原始粒子图像是必要的，以减少背景噪声的影响，从信息源，例如激光的反射。在这个演示中的第一个有效载体位于23微米从墙上。 原始粒子图像后处理使用的的PIV相关性算法，产生的速度矢量场的质量和有效性进行评估。杂散向量在原向量场是不可避免的，但有几个显着特点。不正确的矢量附近的表面是常见的，在边缘处的光的片材，并在边缘ö发流。另外，无效的矢量的大小和方向的不同的显着从相邻的载体，将无法进行物理意义。在此边界层流的例子的情况下，有效的速度矢量指向从左至右，从图2中的颗粒的位移的指示。此外，该速度应减少的壁附近的无滑移条件9。 图3中所示的瞬时速度场适合这些物理条件。另一种有用的度量PIV结果的有效性进行评估，以确定在速度矢量场的每​​个矢量的矢量选择。在一般情况下，矢量场&gt; = 95％的第一选择载体的组成， 即那些需要无需后处理，从而使强大的后处理算法可用于检测和替换不产生相当大的工件2的杂散载体。的瞬时向量中所示的字段<s阮富仲图3是由完全的第一选择载体。 高速，或电影，PIV测量的意义变得显而易见的，从流的图像的时间序列的检查。上面的记录序列的开始，中间和结束的瞬时速度（V）和速度变动（V&#39;）的向量场示于图3。使用的雷诺数分解，V i是平均流速场的总和（ <img alt="方程" fo:src="/files/ftp_upload/50559/50559eq2highres.jpg" src="/files/ftp_upload/50559/50559eq2.jpg" /> ） 和V&#39;10。在这个实验中， <img alt="方程" fo:src="/files/ftp_upload/50559/50559eq2highres.jpg" src="/files/ftp_upload/50559/50559eq2.jpg" />乃平均时间序列中的所有图像。通过瞬时向量场出的记录顺序非常相似，从左侧到右侧显示的流量。这些结果还表明，流动主要是在水平方向上，因为水平速度分量（u）是远大于垂直速度分量（五 ）。波动向量场的水平速度波动（U&#39;）大于垂直速度波动（V&#39;）的 。然而，波动也表明，流动被放慢，因为u值在整个记录序列中改变方向。 U -时间平均和瞬时分布在几个不同的时间在整个记录序列， 如图4所示，验证的流量随着时间的推移正在放缓。 U -型材重新确定通过平均4个相邻的矢量列，共同提高紧贴墙壁的结果的统计学意义。该程序是用在以往的工作6,8。误差线表示的四个相邻的向量列的标准偏差的两倍。最大误差酒吧附近发生的板面上，并重申播种密度低的地区使用的PIV相关性算法的难度。一些分析算法旨在解决播种密度低，如PTV 5,6和时间平均相关方法7,8。 <img alt="图1" src="/files/ftp_upload/50559/50559fig1.jpg" /> 图1。台式组装。 <img alt="图2" fo:content-width="5.5in" fo:src="/files/ftp_upload/50559/50559fig2highres.jpg" src="/files/ftp_upload/50559/50559fig2.jpg" /> 图2。在一个32 x 32像素的讯问壁附近的粒子图像A）T = 0.2毫秒和b）吨= 0.4毫秒的询问窗口的物理尺寸是96×96微米2。 <img alt="图3" src="/files/ftp_upload/50559/50559fig3.jpg" /> 图3。在左边：瞬时（V I），右：波动（V&#39;）的速度场的记录序列的开头，中间和结尾。向量场完全是由第一选择载体。一个较小的子集矢量场显示的清晰度。 V I字段表示V“由左到右，而相反方向的流动。请注意，只有每第四个矢量列在水平方向上显示的清晰度。另外规模之间的V i和V&#39;字段，速度是不同的，所表示的各图像的左上角。 <img alt="图4" src="/files/ftp_upload/50559/50559fig4.jpg" /> 图4。水平速度（U）型材在不同的时间在整个流程中。时间平均U -轮廓用圆圈所示。误差棒显示在T = 0.1毫秒的个人主页上代表所有其他时间的误差线。历史U -型材的时间显示流量随着时间的推移减少。

Watch this Scientific Journal Video about High-speed Particle Image Velocimetry Near Surfaces at JoVE.com

High-speed Particle Image Velocimetry Near Surfaces

研究瞬变流边界附近，使用高分辨率，高速粒子图像测速（PIV）的一个过程。 PIV是一种非侵入式测量技术适用于任何光学访问的流量通过优化多个参数的限制，例如图像和记录性能，激光表属性，和分析算法。

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 ...

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32.9K 次观看.  University of Michigan. 研究瞬变流边界附近，使用高分辨率，高速粒子图像测速（PIV）的一个过程。 PIV是一种非侵入式测量技术适用于任何光学访问的流量通过优化多个参数的限制，例如图像和记录性能，激光表属性，和分析算法。

视频: High-speed Particle Image Velocimetry Near Surfaces

Echo Particle Image Velocimetry

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.2 For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.3,4,5,6 In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine7 with a PC running commercial particle image velocimetry (PIV) software8 is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported.
For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/&delta;t. (See 9 for a review of ultrasound imaging.)
For a typical EPIV experiment, the frame rate is between 20-60 fps, depending on flow conditions, and 100-1000 B-mode images of the spatial distribution of the tracer particles in the flow are acquired. Once acquired, the B-mode ultrasound images are transmitted via an ethernet connection to the PC running the PIV commercial software. Using the PIV software, tracer particle displacement fields, D(x,y)[pixels], (where x and y denote horizontal and vertical spatial position in the ultrasound image, respectively) are acquired by applying cross correlation algorithms to successive ultrasound B-mode images.10 The velocity fields, u(x,y)[m/s], are determined from the displacements fields, knowing the time step between image pairs, &Delta;T[s], and the image magnification, M[meter/pixel], i.e., u(x,y) = MD(x,y)/&Delta;T. The time step between images &Delta;T = 1/fps + D(x,y)/B, where B[pixels/s] is the time it takes for the ultrasound probe to sweep across the image width. In the present study, M = 77[&mu;m/pixel], fps = 49.5[1/s], and B = 25,047[pixels/s]. Once acquired, the velocity fields can be analyzed to compute flow quantities of interest.

An echo particle image velocimetry (EPIV) system capable of acquiring two-dimensional fields of velocity in optically opaque fluids or through optically opaque geometries is described, and validation measurements in pipe flow are reported.

回声粒子图像测速技术

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 ...

科研

工程学

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

在固体氧化物燃料电池电极表面的探测和测绘

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

制备纳米设计的脉冲激光沉积透明导电氧化物

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

High-resolution, High-speed, Three-dimensional Video Imaging with Digital Fringe Projection Techniques

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth.&#160;However, unlike a stereo-based method, DFP uses a digital video projector to replace one of the cameras1. The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera&#8217;s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation.
Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop.&#160;DFP systems can also achieve the same measurement resolution as the camera.&#160;For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in1-5). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30&#160;Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame6,7.&#160;Binary defocusing DFP methods can achieve even greater speeds8.
Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis9, facial animation10, cardiac mechanics studies11, and fluid surface measurements, but many other potential applications exist.&#160;This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.

This video describes the fundamentals of digital fringe projection techniques, which provide dense 3D measurements of dynamically changing surfaces.&#160;It also demonstrates the design and operation of a high-speed binary defocusing system based on these techniques.

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

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 ...

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their behavior for single stages of a process or even an entire process. For the simulation with occurring particle-particle and particle-wall contacts, the value of the coefficient of restitution is required. It can be determined experimentally. The coefficient of restitution depends on several parameters like the impact velocity. Especially for fine particles the impact velocity depends on the air pressure and under atmospheric pressure high impact velocities cannot be reached. For this, a new experimental setup for free-fall tests under vacuum conditions is developed. The coefficient of restitution is determined with the impact and rebound velocity which are detected by a high-speed camera. To not hinder the view, the vacuum chamber is made of glass. Also a new release mechanism to drop one single particle under vacuum conditions is constructed. Due to that, all properties of the particle can be characterized beforehand.

The coefficient of restitution is a parameter that describes the loss of kinetic energy during collision. Here, a free-fall setup under vacuum conditions is developed to be able to determine the coefficient of restitution parameter for particles in micrometer range with high impact velocities.

实验装置的研制归还系数在真空条件下测量

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their ...

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 ...

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. Optical property evaluation of thin films and the surfaces of bulk materials is an important step in understanding new optical material systems and their applications. The method presented can estimate thickness, refractive index, and use absorptive properties of materials for detection. This metrology system uses evanescent field-based photoacoustics (EFPA), a field of research based upon the interaction of an evanescent field with the photoacoustic effect. This interaction and its resulting family of techniques allow the technique to probe optical properties within a few hundred nanometers of the sample surface. This optical near field allows for the highly accurate estimation of material properties on the same scale as the field itself such as refractive index and film thickness. With the use of EFPA and its sub techniques such as total internal reflection photoacoustic spectroscopy (TIRPAS) and optical tunneling photoacoustic spectroscopy (OTPAS), it is possible to evaluate a material at the nanoscale in a consolidated instrument without the need for many instruments and experiments that may be cost prohibitive.

Here we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. This technique evanescent field-based photoacoustics can be used to create a photoacoustic metrology system to estimate materials&#39; thicknesses, bulk and thin film refractive indices, and explore their optical properties.

基于渐逝场光声：光学性能评估在表面

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. ...

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as aqueous solutions and biomaterials, with fast acquisition times. Here, we discuss the assembly and operation of a Brillouin spectrometer that uses stimulated Brillouin scattering (SBS) to measure stimulated Brillouin gain (SBG) spectra of water and lipid emulsion-based tissue-like samples in transmission mode with &lt;10 MHz spectral-resolution and &lt;35 MHz Brillouin-shift measurement precision at &lt;100 ms. The spectrometer consists of two nearly counter-propagating continuous-wave (CW) narrow-linewidth lasers at 780 nm whose frequency detuning is scanned through the material Brillouin shift. By using an ultra-narrowband hot rubidium-85 vapor notch filter and a phase-sensitive detector, the signal-to-noise-ratio of the SBG signal is significantly enhanced compared to that obtained with existing CW-SBS spectrometers. This improvement enables measurement of SBG spectra with up to 100-fold faster acquisition times, thereby facilitating high spectral-resolution and high-precision Brillouin analysis of soft materials at high speed.

We describe the construction of a rapid continuous-wave-stimulated-Brillouin-scattering (CW-SBS) spectrometer. The spectrometer employs single-frequency diode-lasers and an atomic vapor notch-filter to acquire transmission spectra of turbid/non-turbid samples with high spectral-resolution at speeds up to 100-fold faster than those of existing CW-SBS spectrometers. This improvement enables high-speed Brillouin material analysis.

用于材料分析的高速连续波受激布里渊散射光谱仪

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...