Schlieren Image Velocimetry of Swirl Sprays

IF 2 3区工程技术 Q3 MECHANICS

Flow, Turbulence and Combustion Pub Date : 2022-10-30 DOI:10.1007/s10494-022-00385-z

Danilo Almeida Machado, Fernando de Souza Costa, José Carlos de Andrade, Gabriel Silva Dias, Gustavo Alexandre Achilles Fischer

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引用次数: 3

Abstract

Schlieren image velocimetry (SIV) is based on light deflection through flow heterogeneities and image cross-correlations. This is a low-cost and relatively low complexity technique that allows measurement of the droplet velocity field in a large region of a spray. A Z-type Toepler schlieren system with a high-speed camera was used to determine mean vertical and horizontal droplet velocities, as well as the cone angles of sprays produced by a pressure swirl injector with characteristic geometric constant K = 2. Different LEDs and digital filters were evaluated for edge detection and improvement of image contrast. Open software was adopted for digital image processing and velocimetry. Interrogation windows and overlaps of different sizes were tested to obtain an appropriate correlation for determination of the velocity field. The digital images were obtained with 5 × 10³ fps and a resolution of 2.77 pixels/mm. Since the swirl sprays analysed presented instabilities, a number of 100 cross-correlations of images was required to reduce mean velocity fluctuations. Injection pressures varied from 0.05 to 7 bar and mass flow rates varied from 1.389 to 13.89 g/s, using water as test fluid. The wideband warm white LED with Laplacian or high-pass filters provided velocity data for a larger range of injection pressures. Mean axial velocities varied from 3.3 to 11.3 m/s, approximately, with mean horizontal velocities varying from around 0.17 to 3.3 m/s for pressures from 0.05 to 3.22 bar. The velocity data were compared to microscopic shadowgraphy results, showing a good agreement. Spray cone angles ranged from about 32.5^o to 69.5°, for injection pressures from 0.05 to 7 bar, and results of triangulation with a blue LED were closer to semi-empirical data.

Graphic Abstract

Abstract Image

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旋流喷雾纹影图像测速

纹影图像测速(SIV)是基于流体非均质性引起的光偏转和图像互相关。这是一种低成本和相对低复杂性的技术，可以在喷雾的大区域内测量液滴速度场。采用高速摄像机的z型托普勒纹影系统，测定了特征几何常数K = 2的压力旋流喷射器产生的平均垂直和水平液滴速度以及喷雾锥角。评估了不同led和数字滤波器在边缘检测和图像对比度改善方面的效果。采用开放式软件进行数字图像处理和测速。对不同大小的询问窗口和重叠部分进行了测试，以获得确定速度场的适当相关性。获得了5 × 103 fps的数字图像，分辨率为2.77像素/mm。由于所分析的旋流喷雾存在不稳定性，因此需要100多个图像的相互关联来减少平均速度波动。注射压力范围为0.05 ~ 7bar，质量流量范围为1.389 ~ 13.89 g/s，测试流体为水。带拉普拉斯滤波器或高通滤波器的宽带暖白光LED为更大范围的注入压力提供了速度数据。在0.05 ~ 3.22 bar压力下，平均轴向速度约为3.3 ~ 11.3 m/s，平均水平速度约为0.17 ~ 3.3 m/s。将速度数据与显微影成像结果进行了比较，结果吻合较好。喷射压力为0.05 ~ 7bar，喷射锥角范围约为32.5 ~ 69.5°，蓝色LED三角测量结果更接近半经验数据。图形抽象

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来源期刊

Flow, Turbulence and Combustion 工程技术-力学

CiteScore

5.70

自引率

8.30%

发文量

审稿时长

2 months

期刊介绍： Flow, Turbulence and Combustion provides a global forum for the publication of original and innovative research results that contribute to the solution of fundamental and applied problems encountered in single-phase, multi-phase and reacting flows, in both idealized and real systems. The scope of coverage encompasses topics in fluid dynamics, scalar transport, multi-physics interactions and flow control. From time to time the journal publishes Special or Theme Issues featuring invited articles. Contributions may report research that falls within the broad spectrum of analytical, computational and experimental methods. This includes research conducted in academia, industry and a variety of environmental and geophysical sectors. Turbulence, transition and associated phenomena are expected to play a significant role in the majority of studies reported, although non-turbulent flows, typical of those in micro-devices, would be regarded as falling within the scope covered. The emphasis is on originality, timeliness, quality and thematic fit, as exemplified by the title of the journal and the qualifications described above. Relevance to real-world problems and industrial applications are regarded as strengths.