作者谨此致谢香港研究资助局 (否。GRF526913), 香港创新科技委员会 (不。ITS/334/15FP), 美国海军研究局全球办事处 (不。N00014-16-1-2161) 提供财政支持。

1. 风洞设置
<ol><li>三角洲机翼模型
	<ol>
<li>构造一个三角翼模型从铝, 以扫角φ 75°, 弦长度c 280 毫米, 根跨度b 150 毫米和厚度5毫米。在35°上有两个前导边斜面以修复分离点17 (请参见图 1a)。</li>
	</ol></li>
	<li>风洞设施
	<ol>
<li>在闭环低速风洞中进行实验, 测试部分为2.4 米 (长度) x 0.6 米 (宽) x 0.6 米 (高度), 装有玻璃墙, 允许在实验期间进行光学访问。这种设施的湍流强度应小于0.4%。 注: 在本研究中, 我们采用了香港理工大学的风洞, 具有上述特点。此外, 流速度U∞ 从2.64 米/秒到10.56 米/秒不等, 对应于雷诺数, Re, 从 5 x 104到 2 x 105, 基于三角翼的弦长, 这是典型的飞行范围。无人飞行器 (无人机)。</li>
		<li>根据需要, 使用三种不同的安排 (请参见激光片和照相机的图 1bd), 以观察纵向剖面、跨距截面和横断面的流动结构。安装程序的示意图显示在图 1b中。 注: 本协议详细说明了纵向剖面的设置和测量。</li>
	</ol></li>
	<li>安装三角翼
	<ol>
<li>修正三角翼尾缘上的刺, 这是在一个圆形运动指南用于调整攻击角度 (农产品), α。圆形导轨的中心位于风洞试验区的中心线上。因此, 三角洲机翼的中心始终可以在测试部分的中心。将 "农产品" 调整为α = 34°。</li>
		<li>仔细调整三角洲机翼模型, 以尽量减少任何偏航角和滚动角度, 通过检查读数的角度表和三轴激光水平。在目前的研究中, 这两个角度的不确定性小于0.1°。</li>
	</ol></li>
	<li>设置激光片
	<ol>
<li>分别使用两个激光器来阐明 PIV 测量和烟雾流动可视化的流动结构。<ol>
<li>对于 PIV 测量, 使用双脉冲激光器, 波长为532毫微米和最大能量为600兆焦耳 (可调) 为每个脉冲。用晶体管晶体管逻辑 (TTL) 信号的同步器控制它 (请参见图 1b)。</li>
			<li>对于烟雾流动可视化, 使用波长为 532 nm 的连续激光器, 功率为 1 W。这种连续激光器独立工作。在安装过程中, 使用10% 透射率的中性密度滤波器对激光束进行安全过滤。</li>
		</ol>
</li>
		<li>佩戴合适的激光护目镜。</li>
		<li>调整反射镜, 将激光束引入风洞中。激光光轴与镜面之间的夹角为, 使激光束垂直于三角洲机翼表面. <img alt="Equation 1" src="/files/ftp_upload/57244/57244eq1.jpg"> </img>确保激光束位于x/c ≅0.25 的位置, 稍后将成为视图领域的中心 (FOV)。</li>
		<li>安装激光光学 (与连续激光, 首先) 形成激光片, 如图 1b所示。凸透镜用于控制激光束的尺寸 (也适用于板厚)。圆柱透镜将激光束扩展到激光片上。 注: 在目前的研究中, 圆柱透镜的焦距为700毫米, 圆柱透镜的直径为12毫米。</li>
		<li>通过测量模型上的激光线, 检查激光片的厚度。如果激光片厚度不合适, 调整凸透镜的位置 (在这里, 大约1毫米, 以有效宽度的激光片在测试部分大约100毫米)。注意, 激光片的厚度依赖于 1) 的速度分量在正常方向的激光片和 2) 的时间间隔之间的两个快照的 PIV 测量。</li>
		<li>在三角翼上放置一个校准目标板, 其表面与激光片重合。这一步是必不可少的, 因为 FOV 在目前的研究是不正交的风洞坐标。</li>
	</ol></li>
	<li>摄像头设置
	<ol>
<li>设置相机时关掉激光器。与激光一样, 在这个实验的每个单独的部分使用两个摄像头:<ol>
<li>对于 PIV 测量, 请使用一个分辨率为 2048年 x 2048 像素的高速 CCD 摄像机。此摄像机由同步器和双脉冲激光器控制 (请参阅图 1b)。此相机中的数据将直接传送到计算机。</li>
			<li>对于烟雾流可视化, 在烟雾流可视化过程中, 使用具有 4000 x 6000 像素快照分辨率的商用数码相机和 50 Hz 视频记录分辨率 720 x 1280 像素。它将手动操作。</li>
		</ol>
</li>
		<li>移动相机的位置 (商用数码相机, 首先), 以获得所需的 FOV。调整相机镜头, 聚焦在校准靶板上。请确保整个字段都是集中的。如果没有, 相机的坐标可能不是正交的校准目标板。因此, 请仔细调整相机的位置18。</li>
		<li>相机设置好后, 采取几帧。随后, 标定目标板的这些帧将用于校准实际尺寸和帧像素之间的比例因子, 并识别 xyz 坐标中的参考位置。然后, 卸下校准目标板。</li>
	</ol></li>
	<li>以低速 (例如, 3 米/秒) 打开风洞, 并将油粒子注入风洞。将气溶胶发生器的压力设置在2.5 巴, 并在三十年代对预播种流可视化方法进行操作。在此之后, 整个风洞将被均匀地播种与油颗粒在正常直径约1µm。 注: 在目前的研究中, 在烟气流动可视化中, 风洞中的估计油粒密度浓度约为; <img alt="Equation 2" src="/files/ftp_upload/57244/57244eq2.jpg">因此, 风洞中的总流量密度变化为. <img alt="Equation 3" src="/files/ftp_upload/57244/57244eq3.jpg"> </img></li>
	<li>PIV 软件设置
	<ol>
<li>用 piv 软件控制 piv 系统 (见材料表)。此软件可以命令同步器向激光器和照相机发送 TTL 信号, 如图 1b所示。</li>
		<li>将采样频率设置为5赫兹, 总采样数为500。PIV 帧之间的时间间隔为80µs. 请注意, 时间间隔取决于 FOV 和流速的大小。请确保两帧中的审讯区域有大约 50-75% 重叠。</li>
	</ol></li>
</ol>2. 运行实验
<ol><li>
改进的烟雾流动可视化
	<ol>
<li>以所需的流速度打开风洞 (U = 2.64 米/秒)。运行10分钟, 以稳定流速度。在Re = 5万, 流速度为U = 2.64 米/秒。</li>
		<li>打开连续激光器。使用数码相机捕捉流结构的 5-10 快照。</li>
		<li>检查激光片是否位于列芯的纵向截面上 (请参阅图 3中显示的典型结构)。如果是这样, 在三角洲机翼模型上标记这个位置, 作为以后 PIV 测量的参考;否则, 通过调整光学透镜来改变激光片的位置, 并在 1.4.6 1.5.3 的步骤后复位校准。</li>
		<li>查看这些图像并检查焦点和亮度。如果图像质量不理想, 则调整透镜的光圈或 ISO 设置。</li>
		<li>采取更多的快照 (通常大约 20) 和视频 (大约四十年代) 与正确的设置。关闭激光并将数据传输到计算机。</li>
	</ol>
</li>
	<li>
PIV 测量
	<ol>
<li>根据从步骤2.1.3 已知的引用位置和步骤2.1.5 中快照的结果, 选择一个有趣的区域 (x/c≈ 0.3) 作为 FOV, 在那里可以观察到涡流子结构。用双脉冲激光和 CCD 摄像机代替连续激光和数码相机进行 PIV 测量。</li>
		<li>重复步骤 1.4.6 1.5.3 记录 PIV 测量的校准。</li>
		<li>以所需的流速度打开风洞, U = 2.64 米/秒. 运行10分钟以确保流速度稳定。</li>
		<li>将双脉冲激光器调整到最高功率水平并待命。使用该软件启动100s 的数据获取。数据记录完成后, 关闭激光头。</li>
		<li>回顾软件中获取的图像, 检查激光片的分布、粒子密度 (每个所需的审问区域中通常有6-10 粒子)、焦点以及双帧之间的粒子位移 (25-50% 的审讯区域)。</li>
		<li>如果图像的质量令人满意, 如步骤2.2.5 中所述, 请将数据保存到 PC 的硬盘上, 然后通过重复上述步骤来运行其他情况。否则, 请重复步骤1.7 和 2.2, 并仔细调整安装程序。</li>
	</ol>
</li>
</ol>3. 数据处理
<ol><li>
改进的烟雾可视化 注意: 以下步骤 3.1. 1-3. 1.4, 是通过 MATLAB 代码自动完成的 (请参阅补充编码文件)。<ol>
<li>将视频转换为帧序列。将帧从 RGB 窗体转换为灰度。旋转框架使三角翼表面水平。为以后的处理选择感兴趣的区域 (图 2a)。</li>
		<li>调整亮度和对比度以突出显示流结构。应用自适应阈值将灰度图像转换为二进制图像 (图 2b)。</li>
		<li>将每列中的二进制值相加, 并查找总和突然更改的位置。此位置是涡流击穿位置 (图 2c)。</li>
		<li>记录涡流击穿位置及其相应的时间。因而可以获得击穿振荡的时间历史。</li>
		<li>使用像素-实际大小比例因子 (从图像中测量的步骤1.5.3 中的校准目标板), 将时间历史从像素转换为实际大小, 并识别参考位置。绘制故障振荡的时间历史记录。</li>
	</ol>
</li>
	<li>
PIV 测量
	<ol>
<li>运行 PIV 软件。使用步骤2.2.2 中获取的图像设置坐标的比例因子和参考位置。通过图像处理库预先处理获取的数据, 以突出显示粒子并减少噪音18。</li>
		<li>使用自适应审讯区域方法, 其最小网格大小为 32 x 32 像素, 最小重叠为50%。选择图像区域, 并为自适应交叉关联设置 3 x 3 向量验证。</li>
		<li>结果作为一个速度向量场, 其中蓝色向量是正确的向量, 绿色的是取代向量, 红色的是坏的向量。</li>
		<li>应用 3 x 3 移动平均验证方法, 通过比较邻域中的向量来估计局部速度。用邻居的平均值替换离邻居太远的向量。</li>
		<li>计算速度图中的矢量统计量, 以获取时间历史中的流特性,例如、时间平均速度、标准偏差和速度分量之间的相互关联。计算矢量图中的标量导数, 以证明流场的内部特征,例如、涡度、剪切应力和旋转强度。</li>
	</ol>
</li>
</ol>

<ol>
	<li>Smits, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Flow visualization: Techniques and examples. , (2012).</li><li>Barlow, J. B., Rae, W. H., Pope, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Low-speed wind tunnel testing. , (1999).</li><li>Merzkirch, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Flow visualization. , (1987).</li><li>Raffel, M., Willert, C. E., Wereley, S., Kompenhans, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Particle image velocimetry: A practical guide. , (2007).</li><li>Westerweel, J., Elsinga, G. E., Adrian, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Particle+Image+Velocimetry+for+Complex+and+Turbulent+Flows.">Particle Image Velocimetry for Complex and Turbulent Flows.</a> Annu Rev Fluid Mech. 45 (1), 409-436 (2013).</li><li>Meinhart, C. D., Wereley, S. T., Santiago, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PIV+measurements+of+a+microchannel+flow.">PIV measurements of a microchannel flow.</a> Exp Fluids. 27 (5), 414-419 (1999).</li><li>Gursul, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review+of+unsteady+vortex+flows+over+slender+delta+wings.">Review of unsteady vortex flows over slender delta wings.</a> J Aircraft. 42 (2), 299-319 (2005).</li><li>Gursul, I., Gordnier, R., Visbal, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unsteady+aerodynamics+of+nonslender+delta+wings.">Unsteady aerodynamics of nonslender delta wings.</a> Prog Aerosp Sci. 41 (7), 515-557 (2005).</li><li>Lowson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Some+experiments+with+vortex+breakdown.">Some experiments with vortex breakdown.</a> JRoy Aeronaut Soc. 68, 343-346 (1964).</li><li>Payne, F. M., Ng, T., Nelson, R. C., Schiff, L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+and+wake+surveys+of+vortical+flow+over+a+delta+wing.">Visualization and wake surveys of vortical flow over a delta wing.</a> AIAA J. 26 (2), 137-143 (1988).</li><li>Lowson, M. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+three+dimensional+vortex+sheet+structure+on+delta+wings.">The three dimensional vortex sheet structure on delta wings.</a> Fluid Dynamics of Three-Dimensional Turbulent Shear Flows and Transition. , 11.11-11.16 (1989).</li><li>Riley, A. J., Lowson, M. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+three-dimensional+free+shear+layer.">Development of a three-dimensional free shear layer.</a> J Fluid Mech. 369, 49-89 (1998).</li><li>Menke, M., Gursul, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unsteady+nature+of+leading+edge+vortices.">Unsteady nature of leading edge vortices.</a> Phys Fluids. 9 (10), 2960 (1997).</li><li>Yayla, S., Canpolat, C., Sahin, B., Akilli, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Yaw+angle+effect+on+flow+structure+over+the+nonslender+diamond+wing.">Yaw angle effect on flow structure over the nonslender diamond wing.</a> AIAA J. 48 (10), 2457-2461 (2010).</li><li>Menke, M., Gursul, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonlinear+response+of+vortex+breakdown+over+a+pitching+delta+Wing.">Nonlinear response of vortex breakdown over a pitching delta Wing.</a> J Aircraft. 36 (3), 496-500 (1999).</li><li>Sahin, B., Yayla, S., Canpolat, C., Akilli, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+structure+over+the+yawed+nonslender+diamond+wing.">Flow structure over the yawed nonslender diamond wing.</a> Aerosp Sci Technol. 23 (1), 108-119 (2012).</li><li>Kohlman, D. L., Wentz, J. W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vortex+breakdown+on+slender+sharp-edged+wings.">Vortex breakdown on slender sharp-edged wings.</a> J Aircraft. 8 (3), 156-161 (1971).</li><li>Lu, 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+Particle+Image+Velocimetry+Near+Surfaces.">High-speed Particle Image Velocimetry Near Surfaces.</a> J Vis Exp. (76), e50559 (2013).</li><li>Mitchell, A. M., Barberis, D., Molton, P., D&#233;lery, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oscillation+of+Vortex+Breakdown+Location+and+Blowing+Control+of+Time-Averaged+Location.">Oscillation of Vortex Breakdown Location and Blowing Control of Time-Averaged Location.</a> AIAA J. 38 (5), 793-803 (2000).</li><li>Shen, L., Wen, C. -. y., Chen, H. -. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetric+Flow+Control+on+a+Delta+Wing+with+Dielectric+Barrier+Discharge+Actuators.">Asymmetric Flow Control on a Delta Wing with Dielectric Barrier Discharge Actuators.</a> AIAA J. 54 (2), 652-658 (2016).</li><li>Leibovich, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Structure+of+Vortex+Breakdown.">The Structure of Vortex Breakdown.</a> Annu Rev Fluid Mech. 10 (1), 221-246 (1978).</li><li>Mitchell, A. M., Molton, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vortical+Substructures+in+the+Shear+Layers+Forming+Leading-Edge+Vortices.">Vortical Substructures in the Shear Layers Forming Leading-Edge Vortices.</a> AIAA J. 40 (8), 1689-1692 (2002).</li><li>Gad-El-Hak, M., Blackwelder, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+discrete+vortices+from+a+delta+wing.">The discrete vortices from a delta wing.</a> AIAA J. 23 (6), 961-962 (1985).</li><li>Zhou, J., Adrian, R. J., Balachandar, S., Kendall, T. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+for+generating+coherent+packets+of+hairpin+vortices+in+channel+flow.">Mechanisms for generating coherent packets of hairpin vortices in channel flow.</a> J. Fluid Mech. 387, 353-396 (1999).</li><li>Adrian, R. J., Christensen, K. T., Liu, Z. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+and+interpretation+of+instantaneous+turbulent+velocity+fields.">Analysis and interpretation of instantaneous turbulent velocity fields.</a> Exp Fluids. 29 (3), 275-290 (2000).</li><li>Yoda, M., Hesselink, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+three-dimensional+visualization+technique+applied+to+flow+around+a+delta+wing.">A three-dimensional visualization technique applied to flow around a delta wing.</a> Exp. Fluids. 10 (2-3), (1990).</li><li>Greenwell, D. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> RTO AVT Symposium. , (2001).</li><li>Furman, A., Breitsamter, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Turbulent+and+unsteady+flow+characteristics+of+delta+wing+vortex+systems.">Turbulent and unsteady flow characteristics of delta wing vortex systems.</a> Aerosp Sci Technol. 24 (1), 32-44 (2013).</li><li>Wang, C., Gao, Q., Wei, R., Li, T., Wang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+flow+visualization+and+tomographic+particle+image+velocimetry+for+vortex+breakdown+over+a+non-slender+delta+wing.">3D flow visualization and tomographic particle image velocimetry for vortex breakdown over a non-slender delta wing.</a> Exp Fluids. 57 (6), (2016).</li></ol>

作者没有什么可透露的。

本文介绍了两种流动可视化方法, 改进了烟气流动可视化和 PIV 测量, 对三角洲机翼的流动结构进行了定性和定量的研究。对实验的一般程序进行了逐步的描述。这两种方法的设置几乎相同, 而所涉及的设备则不同。这两种流动可视化方法的基本原理是通过激光片来照亮流动中的粒子。改进后的烟气流动可视化可以同时获得全局流结构和小局部结构, 有助于获得未知流结构的概述。定量 PIV 分析提供?...

通过可视化技术进行流场测量是流体工程的基本方法。在不同的可视化技术中, 风洞实验中的烟线流动可视化和水隧道实验中的染料可视化, 是对渗流结构进行定性描述的最广泛的应用。PIV 和激光多普勒测速技术 (LDA) 是两种典型的定量技术 1.
在烟雾线流动可视化中, 烟雾 streaklines 是由加热导线上的油滴产生的, 或在实验过程中从外层烟雾发生器/容器中注入。大功率灯或激光片用于照亮烟雾 streaklines。然后记录图像以进行进一步分析。这是一个简单但非常有用的流可视化方法2。然而, 这种方法的有效性可能受到各种因素的限制, 如烟线的短时间, 复杂的三维流场, 相对较高的流速和烟雾产生的效率3。
在 PIV 测量中, 带有气流粒子的流场的剖面由激光片照亮, 在这个剖面中粒子的瞬时位置被高速相机捕获。在极小的时间间隔内, 记录一对图像。通过将图像分割成一个审讯区网格, 通过交叉相关函数计算审讯区域内粒子的平均运动, 可以得到观测到的剖面上的瞬时速度矢量图。然而, 也知道, 必须达成妥协的因素, 包括观察窗口的大小, 速度图的分辨率, 平面的速度大小, 对图像的时间间隔, 正交速度大小和粒子密度4。因此, 可能需要进行许多探索性实验以优化实验设置。用 PIV 测量单独的5、6来调查未知和复杂的流场将是昂贵且耗时的。针对上述问题, 提出了一种结合烟气流动可视化和 PIV 测量的策略, 并在此基础上对细长三角洲机翼上的复杂流动进行了研究。
在三角洲机翼上进行的比对列的大量研究已经进行了7、8, 并使用流可视化技术作为主要工具。许多有趣的流现象被观察到: 螺旋型和气泡式涡击穿9,10, 不稳定剪切层子结构11,12, 列弗击穿位置的振荡13, 以及俯仰和偏航角度14、15、16在流结构上的影响。然而, 三角洲翼流中某些不稳定现象的基本机制仍然不清楚7。在这项工作中, 烟雾流动可视化的改进使用相同的播种粒子用于 PIV 测量, 而不是烟雾线。这种改进大大简化了可视化的操作, 提高了图像的质量。基于改进的烟气流动可视化结果, PIV 测量主要集中在感兴趣的流场上获取定量信息。
本文详细介绍了如何在风洞中进行流动可视化实验, 并研究了三角洲机翼上的非恒定流现象。本实验将两种可视化方法、改进的烟气流动可视化和 PIV 测量相结合使用。该过程包括设备设置和参数调整的分步指导。典型的结果表明, 结合这两种方法来测量复杂的流场的空间和世俗的优势。

<table><tbody><tr><td>532 nm Nd:YAG laser</td><td>Quantel Laser</td><td>Evergreen 600mJ</td><td></td></tr><tr><td>High speed camera</td><td>Dantec Dynamic</td><td>HiSense 4M</td><td></td></tr><tr><td>camera lens</td><td>Tamron</td><td>SP AF180mm F/3.5 Di</td><td></td></tr><tr><td>PIV recording and processing software</td><td>Dantec Dynamic</td><td>DynamicStudio</td><td></td></tr><tr><td>cylindrical lens</td><td>Newport</td><td></td><td>&amp;Phi;=12 mm</td></tr><tr><td>convex lens</td><td>Newport</td><td></td><td>f=700 mm</td></tr><tr><td>neutral density filter</td><td>Newport</td><td></td><td></td></tr><tr><td>Calibration target</td><td></td><td></td><td>custom made</td></tr><tr><td>aerosol generator</td><td>TSI</td><td>TSI 9307-6</td><td></td></tr><tr><td>PULSE GENERATOR</td><td>Berkeley Nucleonics Corp</td><td>BNC 575</td><td></td></tr><tr><td>continuous laser</td><td></td><td>APGL-FN-532-1W</td><td></td></tr><tr><td>Digital camera</td><td>Nikon</td><td>Nikon D5200</td><td></td></tr><tr><td>Image processing</td><td>Matlab</td><td></td><td>custom code</td></tr><tr><td>wind tunnel support</td><td></td><td></td><td>custom made</td></tr><tr><td>laser level</td><td>BOSCH</td><td>GLL3-15X</td><td></td></tr><tr><td>angle meter</td><td>BOSCH</td><td>GAM220</td><td></td></tr></tbody></table>

experimental investigation of the flow structure over a delta wing via flow visualization methods

众所周知, 三角洲机翼上的流场由一对反旋转前缘涡 (列列) 控制。然而, 他们的机制还没有得到很好的理解。流场可视化技术是一种很有前途的非侵入性方法, 可以在空间和世俗上说明复杂的流动。一个基本的流可视化设置由高功率的激光和光学透镜组成, 用于生成激光片、照相机、示踪粒子发生器和数据处理器。风洞的设置, 所涉及的设备的规格, 以及相应的参数设置取决于要获得的流量特征。
正常的烟线流动可视化使用烟线来证明流动 streaklines。然而, 在复杂流场中, 由于空间分辨率差, 该方法的性能受到限制。为此, 研制了一种改进的烟气流动可视化技术。该技术同时说明了大规模的全球列流场和小尺度剪切层流结构, 为以后详细的粒子图像测速 (PIV) 测量提供了宝贵的参考。
本文介绍了改进的烟气流动可视化和 PIV 测量在三角洲机翼非恒定流现象研究中的应用。列举了风洞安装、数据采集、数据处理等实验过程和注意事项。结果表明, 这两种流动可视化方法是对三维流场进行定性和定量研究的有效方法。

图 2d显示了列在分解位置的时间历史记录。黑色曲线表示左舷, 红色曲线指示右舷列列。时间尺度由自由流速度和弦长 nondimensionalized。这两次历史的相关系数为r = −0.53, 表明了列的击穿位置振荡的强反对称相互作用。此结果与其他13、19、20的工作很好地吻合。
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Watch this Scientific Journal Video about Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods at JoVE.com

Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods

在这里, 我们提出了一种通过改进的烟雾流可视化技术来观察三角洲机翼上非恒定涡流流的协议, 并研究了导致前缘涡击穿位置振荡的机制。

基于流动可视化方法的三角洲机翼流动结构实验研究

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is ...

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Unit 1

Flow over Immersed Bodies

Force Vectors

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10.5K 次观看.  Hong Kong Polytechnic University. 在这里, 我们提出了一种通过改进的烟雾流可视化技术来观察三角洲机翼上非恒定涡流流的协议, 并研究了导致前缘涡击穿位置振荡的机制。

视频: Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods

Investigating the Three-dimensional Flow Separation Induced by a Model Vocal Fold Polyp

The fluid-structure energy exchange process for normal speech has been studied extensively, but it is not well understood for pathological conditions. Polyps and nodules, which are geometric abnormalities that form on the medial surface of the vocal folds, can disrupt vocal fold dynamics and thus can have devastating consequences on a patient&#39;s ability to communicate. Our laboratory has reported particle image velocimetry (PIV) measurements, within an investigation of a model polyp located on the medial surface of an in&#160;vitro driven vocal fold model, which show that such a geometric abnormality considerably disrupts the glottal jet behavior. This flow field adjustment is a likely reason for the severe degradation of the vocal quality in patients with polyps. A more complete understanding of the formation and propagation of vortical structures from a geometric protuberance, such as a vocal fold polyp, and the resulting influence on the aerodynamic loadings that drive the vocal fold dynamics, is necessary for advancing the treatment of this pathological condition. The present investigation concerns the three-dimensional flow separation induced by a wall-mounted prolate hemispheroid with a 2:1 aspect ratio in cross flow, i.e. a model vocal fold polyp, using an oil-film visualization technique. Unsteady, three-dimensional flow separation and its impact of the wall pressure loading are examined using skin friction line visualization and wall pressure measurements.

Vocal fold polyps can disrupt vocal fold dynamics and thus can have devastating consequences on a patient&#39;s ability to communicate. Three-dimensional flow separation induced by a wall-mounted model polyp and its impact on the wall pressure loading are examined using particle image velocimetry, skin friction line visualization, and wall pressure measurements.

研究模型声乐折叠聚合物引起的三维流量分离

The fluid-structure energy exchange process for normal speech has been studied extensively, but it is not well understood for pathological conditions. ...

科研

生物工程

Experimental Investigation of Secondary Flow Structures Downstream of a Model Type IV Stent Failure in a 180&#176; Curved Artery Test Section

The arterial network in the human vasculature comprises of ubiquitously present blood vessels with complex geometries (branches, curvatures and tortuosity). Secondary flow structures are vortical flow patterns that occur in curved arteries due to the combined action of centrifugal forces, adverse pressure gradients and inflow characteristics. Such flow morphologies are greatly affected by pulsatility and multiple harmonics of physiological inflow conditions and vary greatly in size-strength-shape characteristics compared to non-physiological (steady and oscillatory) flows 1 - 7.
Secondary flow structures may ultimately influence the wall shear stress and exposure time of blood-borne particles toward progression of atherosclerosis, restenosis, sensitization of platelets and thrombosis 4 - 6, 8 - 13. Therefore, the ability to detect and characterize these structures under laboratory-controlled conditions is precursor to further clinical investigations.
A common surgical treatment to atherosclerosis is stent implantation, to open up stenosed arteries for unobstructed blood flow. But the concomitant flow perturbations due to stent installations result in multi-scale secondary flow morphologies 4 - 6. Progressively higher order complexities such as asymmetry and loss in coherence can be induced by ensuing stent failures vis-&#224;-vis those under unperturbed flows 5. These stent failures have been classified as &#34;Types I-to-IV&#34; based on failure considerations and clinical severity 14.
This study presents a protocol for the experimental investigation of the complex secondary flow structures due to complete transverse stent fracture and linear displacement of fractured parts (&#34;Type IV&#34;) in a curved artery model. The experimental method involves the implementation of particle image velocimetry (2C-2D PIV) techniques with an archetypal carotid artery inflow waveform, a refractive index matched blood-analog working fluid for phase-averaged measurements 15 - 18. Quantitative identification of secondary flow structures was achieved using concepts of flow physics, critical point theory and a novel wavelet transform algorithm applied to experimental PIV data 5, 6, 19 - 26.

Stent implants in stenosed arterial curvatures are prone to "Type IV" failures involving the complete transverse fracture of stents and linear displacement of the fractured parts. We present a protocol for detection of secondary flow (vortical) structures in a curved artery model, downstream of clinically relevant "Type IV" stent failures.

在180°弧形动脉试验段的二次流动结构下游的型号IV型支架失败的实验研究

The arterial network in the human vasculature comprises of ubiquitously present blood vessels with complex geometries (branches, curvatures and ...

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 ...

工程学

Airfoil Behavior: Pressure Distribution over a Clark Y-14 Wing

Source: David Guo, College of Engineering, Technology, and Aeronautics (CETA), Southern New Hampshire University (SNHU), Manchester, New Hampshire
An airfoil is a 2-dimensional wing section that represents critical wing performance characteristics. The pressure distribution and lift coefficient are important parameters that characterize the behavior of airfoils. The pressure distribution is directly related to the lift generated by airfoils. A Clark Y-14 airfoil, which is used in this demonstration, has a thickness of 14% and is flat on the lower surface from 30% of chord length to the back.
Here we will demonstrate how the pressure distribution around an airfoil is measured using a wind tunnel. A Clark Y-14 airfoil model with 19 pressure ports is used to collect pressure data, which is used to estimate the lift coefficient.

机翼行为:克拉克Y-14翼上的压力分布

Source: David Guo, College of Engineering, Technology, and Aeronautics (CETA), Southern New Hampshire University (SNHU), Manchester, New Hampshire
An ...

教育

JoVE Science Education

航空工程

Turbulence Sphere Method: Evaluating Wind Tunnel Flow Quality

Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Wind tunnel tests are useful in the design of vehicles and structures that are subjected to airflow during their use. Wind tunnel data are generated by applying a controlled air flow to a model of the object being studied. The test model usually has a similar geometry but is a smaller scale compared to the full-sized object. To ensure accurate and useful data is collected during low speed wind tunnel tests, there must be a dynamic similarity of the Reynolds number between the tunnel flow field over the testing model and the actual flow field over the full-sized object.
In this demonstration, wind tunnel flow over a smooth sphere with well-defined flow characteristics will be analyzed. Because the sphere has well-defined flow characteristics, the turbulence factor for the wind tunnel, which correlates the effective Reynolds number to the test Reynolds number, can be determined, as well as the free-stream turbulence intensity of the wind tunnel.

Turbulence Measurements at Varying Air Speeds

湍流球法:评估风洞流量质量

Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Wind tunnel tests are useful ...

Cross Cylindrical Flow: Measuring Pressure Distribution and Estimating Drag Coefficients

Source: David Guo, College of Engineering, Technology, and Aeronautics (CETA), Southern New Hampshire University (SNHU), Manchester, New Hampshire
The pressure distributions and drag estimations for cross cylindrical flow have been investigated for centuries. By ideal inviscid potential flow theory, the pressure distribution around a cylinder is vertically symmetric. The pressure distribution upstream and downstream of the cylinder is also symmetric, which results in a zero-net drag force. However, experimental results yield very different flow patterns, pressure distributions and drag coefficients. This is because the ideal inviscid potential theory assumes irrotational flow, meaning viscosity is not considered or taken into account when determining the flow pattern. This differs significantly from reality.
In this demonstration, a wind tunnel is utilized to generate a specified airspeed, and a cylinder with 24 ports of pressure is used to collect pressure distribution data. This demonstration illustrates how the pressure of a real fluid flowing around a circular cylinder differs from predicted results based on the potential flow of an idealized fluid. The drag coefficient will also be estimated and compared to the predicted value.

Cross Cylindrical Flow: Pressure Distribution &amp; Drag Coefficients

交叉圆柱流:测量压力分布和估计阻力系数

Source: David Guo, College of Engineering, Technology, and Aeronautics (CETA), Southern New Hampshire University (SNHU), Manchester, New Hampshire
The ...

Schlieren Imaging: A Technique to Visualize Supersonic Flow Features

Source: Jose Roberto Moreto, Jaime Dorado, and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Military jet fighters and projectiles can fly at incredible speeds that exceed the speed of sound, which means they are traveling at a supersonic speed. The speed of sound is the speed at which a sound wave propagates through a medium, which is 343 m/s. Mach numbers are used to gauge the flight speed of an object relative to the speed of sound.
An object traveling at the speed of sound would have a Mach number of 1.0, whereas an object traveling faster than the speed of sound has a Mach number greater than 1.0. The compressibility effects of air must be accounted for when traveling at such speeds. A flow is considered compressible when the Mach number is greater than 0.3. In this demonstration, Mach 2.0 supersonic flow over a cone will be analyzed by visualizing the formation of shock waves and compression waves in compressible flow using a Schlieren system.

Schlieren Imaging: Visualization of Supersonic Flow Features

施利伦成像:一种可视化超音速流特性的技术

Source: Jose Roberto Moreto, Jaime Dorado, and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Military jet ...

Flow Visualization in a Water Tunnel: Observing the Leading-edge Vortex Over a Delta Wing

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The delta wing, shown in Figure 1D, is a popular design in high-speed airplanes due to its superb performance in transonic and supersonic flight regimes. This type of wing has a small aspect ratio and high sweep angle, which reduces drag at high subsonic, transonic and supersonic flight regimes. The aspect ratio is defined as the wing span divided by the average chord <img align="middle" src="/files/ftp_upload/10459/10459eq1a.jpg" />.
An important advantage of the delta wing is its high stall angle. The stall of a delta wing is delayed compared to the stall of a high aspect ratio wing. This is because the lift of a delta wing is enhanced by the leading-edge vortex over the wing.
An effective way to observe this vortex flow phenomenon and study the vortex breakdown in a delta wing is by visualizing the flow in a water tunnel. By injecting dye in the flow surrounding a model from dye ports on the leading-edge, the vortex development and breakdown can be observed and its position measured. The data can also be used to estimate the stall angle.
<img src="/files/ftp_upload/10459/10459fig1.jpg" />
Figure 1. Typical wing planform shapes: A) Rectangular, with constant chord along span, B) elliptical, C) tapered, with variable chord along the span, and D) delta wing, an aft-swept wing with zero taper ratio.

Flow in a Water Tunnel: Leading-edge Vortex over a Delta Wing

水隧道中的流量可视化:在三角洲翼上观察前沿涡流

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The ...

Surface Dye Flow Visualization: A Qualitative Method to Observe Streakline Patterns in Supersonic Flow

Flow visualization around or on a body is an important tool in aerodynamics research. It provides a method to qualitatively and quantitatively study flow structure, and it also helps researchers theorize and verify fluid flow behavior. Flow visualization can be divided into two categories: off-the-surface visualization and surface flow visualization. Off-the-surface flow visualization techniques involve determining the flow characteristics around the body of interest. They include but are not restricted to particle image velocimetry (PIV), Schlieren imaging, and smoke flow visualization. These techniques can provide qualitative as well as quantitative data on the flow around a body. However, these techniques are generally expensive and difficult to set-up. Surface flow visualization techniques, on the other hand, involve coating the body of interest with a dye to study flow on the surface. These techniques, which are more invasive in practice, include dye flow visualization and, more recently, use pressure-sensitive paint, which gives a detailed image of the flow on the body&#39;s surface. This allows researchers to visualize different flow features, including laminar bubbles, boundary layer transitions, and flow separation. Dye flow visualization, the technique of interest in the current experiment, provides a qualitative picture of the surface flow and is one of the simplest and most cost-effective surface flow visualization methods, specifically for visualizing gaseous flows on a body.
In this experiment, the surface flow behavior on six bodies are studied in supersonic flow. The streakline patterns are obtained using the dye flow visualization technique, and the flow paths, degree of flow attachment and separation, and location and type of shocks are identified and studied from the flow images.

Surface Dye Flow: Streakline Patterns in Supersonic Flow

表面染料流可视化:观察超音速流中条纹模式的定性方法

Flow visualization around or on a body is an important tool in aerodynamics research. It provides a method to qualitatively and quantitatively study flow ...

Measuring Turbulent Flows

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows exhibit very high frequency fluctuations that require instruments with high time-resolution for their appropriate characterization. Hot-wire anemometers have a short enough time-response to fulfill this requirement. The purpose of this experiment is to demonstrate the use of hot-wire anemometry to characterize a turbulent jet.
In this experiment, a previously calibrated hot-wire probe will be used to obtain velocity measurements at different positions within the jet. Finally, we will demonstrate a basic statistical analysis of the data to characterize the turbulent field.

Measuring Turbulent Flows Using Hot-Wire Anemometers

测量紊流

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