论文标题
圆形湍流氦气喷气机的Schlieren和BOS Velocimetry
Schlieren and BOS velocimetry of a round turbulent helium jet in air
论文作者
论文摘要
无籽的速度法正在对许多工业和研究应用中引起人们的兴趣。我们报告了一项使用传统的，镜像的刀具边缘光学的光学速度计的比较研究，以红色= 5,890和11,300的空气中的亚音速圆形湍流氦气的空气中的亚音速圆形湍流氦射流的schlieren（BOS）。具有1024个像素流式分辨率（0 <x/d <200）的数字图像以6000帧/s的速度捕获。通过使用OpenPIV软件以及X-T图（Kymography）的条纹分析对这些结果进行了赛车测定。还收集了有限的PIV数据以验证Schlieren速度测定结果。 BOS和传统的Schlieren都在根据中心线速度的1/X衰减，高斯形径向速度曲线和射流的线性扩散速率来测量平均流helium Jet自相似性方面都显示出部分成功。可视化的湍流涡流（用作Schlieren速度法中的示踪剂）的持续时间比目前的氦气喷射中所需的时间长。同样，在某些结果中，测得的对流速度似乎足够健壮，可以汇总到射流平均速度。 Kymography比DIC产生的总体结果更好，DIC归因于Kymography的喷射速度时空“频谱”，从而使射流中心线附近的快速涡流歧视在射流周围附近的速度较慢。 DIC和其他分析方法遭受了一个平均偏差，会对结果产生负面影响。速度计的基因学数据的降低是手动完成的，也是通过傅立叶转换图像 - 功能定位代码进行的，都产生了等效的结果。
Seedless velocimetry is gaining interest in many industrial and research applications. We report on a comparative study of time-resolved optical velocimetry using traditional, mirror-type knife-edge schlieren optics versus Background-Oriented Schlieren (BOS) of subsonic round turbulent helium jets in air at Red = 5,890 and 11,300. Digital images with 1024 pixels streamwise resolution (0 < x/d < 200) were captured at 6000 frames/s in large ensembles. Velocimetry was performed on these results by digital image correlation (DIC) using OpenPIV software, and by streak-schlieren analysis of x-t diagrams (kymography). Limited PIV data were also collected for verification of the schlieren velocimetry results. Both BOS and traditional schlieren show partial success in measuring the mean-flow helium jet self-similarity in terms of the 1/x decay of centerline velocity, Gaussian-shaped radial velocity profiles, and linear spreading rate of the jet. Visualized turbulent eddies, used as tracers in schlieren velocimetry, are observed to last longer than is necessary for this purpose in the present helium jets. Also, the measured convective velocity appears to be sufficiently robust to sum to the jet mean velocity in some of the results. Kymography yields better overall results than DIC, which we attribute to kymography's spatiotemporal "spectrum" of jet velocities, enabling the discrimination of fast eddies near the jet centerline from slower ones near the jet periphery. DIC and other analysis methods suffer from a path-averaging bias which negatively affects the results. The reduction of kymographic data for velocimetry was done manually and also by a Fourier-transform image-feature-orientation code, both yielding equivalent results.
