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Open AccessArticle

Analysis of the Interconnections between Classic Vortex Models of Coherent Structures Based on DNS Data

College of Civil Engineering, Fuzhou University, Fuzhou 350116, China
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Author to whom correspondence should be addressed.
Water 2019, 11(10), 2005; https://doi.org/10.3390/w11102005
Received: 7 August 2019 / Revised: 21 September 2019 / Accepted: 23 September 2019 / Published: 26 September 2019
(This article belongs to the Special Issue Physical and Mathematical Fluid Mechanics)
Low- and high-speed streaks (ejection, Q2, and sweep, Q4, events in quadrant analysis) are significant features of coherent structures in turbulent flow. Streak formation is closely related to turbulent structures in several vortex models, such as attached eddy models, streamwise vortex analysis models, and hairpin vortex models, which are all standard models. Vortex models are complex, whereby the relationships among the different vortex models are unclear; thus, further studies are still needed to complete our understanding of vortices. In this study, 30 sets of direct numerical simulation (DNS) data were obtained to analyze the mechanics of the formation of coherent structures. Image processing techniques and statistical analysis were used to identify and quantify streak characteristics. We used a method of vortex recognition to extract spanwise vortices in the x–z plane. Analysis of the interactions among coherent structures showed that the three standard vortex models all gave reasonably close results. The attached eddy vortex model provides a good explanation of the linear dimensions of streaky structures with respect to the water depth and Q2 and Q4 events, whereby it can be augmented to form the quasi-streamwise vortex model. The legs of a hairpin vortex envelop low-speed streaky structures and so move in the streamwise direction; lower-velocity vortex legs also gradually accumulate into a streamwise vortex. Statistical analysis allowed us to combine our present results with some previous research results to propose a mechanism for the formation of streaky structures. This study provides a deeper understanding of the interrelationships among different vortex models. View Full-Text
Keywords: image processing; streaky structures; hairpin vortex; attached-eddy vortex; streamwise vortex image processing; streaky structures; hairpin vortex; attached-eddy vortex; streamwise vortex
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MDPI and ACS Style

Wang, H.; Peng, G.; Chen, M.; Fan, J. Analysis of the Interconnections between Classic Vortex Models of Coherent Structures Based on DNS Data. Water 2019, 11, 2005. https://doi.org/10.3390/w11102005

AMA Style

Wang H, Peng G, Chen M, Fan J. Analysis of the Interconnections between Classic Vortex Models of Coherent Structures Based on DNS Data. Water. 2019; 11(10):2005. https://doi.org/10.3390/w11102005

Chicago/Turabian Style

Wang, Hao; Peng, Guoping; Chen, Ming; Fan, Jieling. 2019. "Analysis of the Interconnections between Classic Vortex Models of Coherent Structures Based on DNS Data" Water 11, no. 10: 2005. https://doi.org/10.3390/w11102005

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