Characterization of the fractal dimension of helium plumes in laminar to turbulent transition

IF 2.5 3区工程技术 Q2 ENGINEERING, MECHANICAL Experiments in Fluids Pub Date : 2025-03-07 DOI:10.1007/s00348-025-04001-4

Maria N. D’Orazio, Christian Peterson, Michael J. Hargather

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Abstract

Schlieren imaging in conjunction with a high-speed camera was used to observe the behavior of metered helium plumes as they transition from laminar to turbulent flow in an air environment. The plumes were visualized at twelve jet Reynolds numbers ranging from 200 to 2980. The fractal dimension of the flows was obtained by applying a box counting algorithm to the recorded schlieren images. The results were analyzed to determine the correlation between the Reynolds number of the flow and the fractal dimension of the observed turbulence. A trend of increasing fractal dimension with increasing Reynolds number was observed for several different types of schlieren cutoffs including horizontal cutoff, vertical cutoff, circular cutoff, focused shadowgraphy and de-focused shadowgraphy. The vertical cutoff and focused shadowgraphy imaging methods showed the most consistent results for the fractal dimension characterization during the laminar to turbulent transition. For transitional plumes, it was observed that fractal dimension increased with distance from the jet outlet.

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层流到湍流过渡中氦羽流分形维数的表征

纹影成像与高速相机一起被用来观察测量氦羽流在空气环境中从层流转变为湍流的行为。这些羽流在200到2980之间的12个射流雷诺数下被可视化。通过对记录的纹影图像进行盒计数，得到了流场的分形维数。对实验结果进行了分析，确定了湍流的雷诺数与观测到的湍流分形维数之间的关系。水平截断、垂直截断、圆形截断、聚焦阴影和去聚焦阴影等不同类型纹影截断的分形维数随雷诺数的增加呈增加趋势。垂直截断和聚焦阴影成像方法对层流向湍流过渡过程的分形维数表征结果最为一致。对于过渡羽流，分形维数随距离射流出口的增加而增加。

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来源期刊

Experiments in Fluids 工程技术-工程：机械

CiteScore

5.10

自引率

12.50%

发文量

157

审稿时长

3.8 months

期刊介绍： Experiments in Fluids examines the advancement, extension, and improvement of new techniques of flow measurement. The journal also publishes contributions that employ existing experimental techniques to gain an understanding of the underlying flow physics in the areas of turbulence, aerodynamics, hydrodynamics, convective heat transfer, combustion, turbomachinery, multi-phase flows, and chemical, biological and geological flows. In addition, readers will find papers that report on investigations combining experimental and analytical/numerical approaches.