LOCAL VORTEX IDENTIFICATION CRITERIA: INTER-RELATIONSHIPS AND A UNIFIED OUTLOOK

Vortex identification is important for understanding the physical mechanism of turbulent flow. The common vortex identification techniques based on velocity gradient tensor such as [Formula: see text] criterion will consume a lot of computing resources for processing great quantity of experimental data. To improve the vortex identification efficiency and achieve real-time recognition, we present a novel vortex identification method using segmentation with convolutional neural network (CNN) based on flow field image data, which is named “Butterfly-CNN”. Considering that the view of flow field is small, it is necessary to integrate both the local and global feature maps to achieve higher precision. The architecture consists of an encoded–decoded path, which is similar to [Formula: see text]-net but with different superimposed network part. In the Butterfly-CNN, the cross-expanding paths are designed with the global information to enable precise localization, and the feature maps after each convolution are regarded as the original pictures, then convolute to the size of the last feature map and upsample to the original size again. Finally, the decoded and cross-expanding networks are added up. The Butterfly-CNN can be trained end-to-end from a few images, and it is useful and efficient for vortex identification.

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Combining PIV, POD and vortex identification algorithms for the study of unsteady turbulent swirling flows

Measurement Science and Technology ◽

10.1088/0957-0233/12/9/307 ◽

2001 ◽

Vol 12 (9) ◽

pp. 1422-1429 ◽

Cited By ~ 494

Author(s):

Laurent Graftieaux ◽

Marc Michard ◽

Nathalie Grosjean

Keyword(s):

Swirling Flows ◽

Vortex Identification

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3D tomographic PIV, POD and vortex identification of turbulent slot jet flow impinging on a flat plate

Journal of Mechanical Science and Technology ◽

10.1007/s12206-017-1029-9 ◽

2017 ◽

Vol 31 (11) ◽

pp. 5347-5357 ◽

Cited By ~ 4

Author(s):

Mahmoud Charmiyan ◽

Ahmad Reza Azimian ◽

Ebrahim Shirani ◽

Fethi Aloui ◽

Cedric Degouet ◽

...

Keyword(s):

Flat Plate ◽

Jet Flow ◽

Vortex Identification ◽

Tomographic Piv

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Influence of Upstream Disturbances on the Vortex Structure of Francis Turbine Based on the Criteria of Identification of Various Vortexes

Energies ◽

10.3390/en14227626 ◽

2021 ◽

Vol 14 (22) ◽

pp. 7626

Author(s):

Tao Guo ◽

Lihui Xu ◽

Wenquan Wang

Keyword(s):

Flow Field ◽

Vortex Structure ◽

Draft Tube ◽

Francis Turbine ◽

Vortex Identification ◽

Vortex Rope ◽

Blade Passage ◽

Small Opening ◽

Turbulent Characteristics ◽

Passage Vortex

The inter-blade passage vortex, the vortex rope of the draft tube, and the vortex in the guide apparatus are the characteristics of flow instability of the Francis turbine, which may lead to fatigue failure in serious cases. In the current study, in order to accurately capture the transient turbulent characteristics of flow under different conditions and fully understand the flow field and vortex structure, we conduct a simulation that adopts sliding grid technology and the large-eddy simulation (LES) method based on the wall-adapting local eddy viscosity (WALE) model. Using the pressure iso-surface method, the Q criterion, and the latest third-generation Liutex vortex identification method, this study analyzes and compares the inter-blade passage vortex, the vortex rope of the draft tube, and the outflow and vortex in the guide apparatus, focusing on the capture ability of flow field information by various vortex identification methods and the unique vortex structure under the condition of a small opening. The results indicate that the dependence of Liutex on the threshold is small, and the scale range of the flow direction vortex captured by Liutex is wider, but the ability of the spanwise vortex is relatively weak. The smaller the opening, the more disorderly the vortexes generated in each component and the more unstable the flow field. In the draft tube, the original shape of the vortex rope is destroyed due to the interaction between vortexes. Under the condition of a small opening, an inter-blade passage vortex is generated, affecting the efficient and stable operation of the turbine.

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On the relationships between different vortex identification methods based on local trace criterion

Physics of Fluids ◽

10.1063/5.0063326 ◽

2021 ◽

Vol 33 (10) ◽

pp. 105116

Author(s):

Yangwei Liu ◽

Weibo Zhong ◽

Yumeng Tang

Keyword(s):

Vortex Identification ◽

Identification Methods

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The Four Stage Development of Starting Turbulent Buoyant Plumes

10.1115/fedsm2021-65540 ◽

2021 ◽

Author(s):

Thanh Tran ◽

Kiran Bhaganagar

Keyword(s):

Large Scale ◽

Wildland Fire ◽

Forecast Model ◽

Vortex Identification ◽

Buoyant Plumes ◽

Volcanic Plumes ◽

Turbulence Structures ◽

Eddy Simulation ◽

Stage Development ◽

High Reynolds

Abstract Turbulent heated and buoyant plumes have important applications in the atmosphere such as wildland fire plumes, volcanic plumes, and chemical plumes. The purpose of the study is to analyze the turbulence structures, and to understand the stages of the development of the starting turbulent plumes. For this purpose, data generated from an in-house Weather Research Forecast model coupled with Large-eddy simulation (WRF-bLES) with two-way feedback between the buoyant plume and the atmosphere developed has been used. The release of both dense gases (Co2, So2) and, buoyant gases (He, NH3, heated air) from a circular source at the bottom of the domain have been investigated. The simulations of the axisymmetric plume were performed at a high Reynolds number of 108. Vortex Identification methods were used to extract the Coherent structures and the large-scale features of the flow. The results have demonstrated that both the dense and the buoyant heated plumes with different initial characters exhibited universal characteristics and the development of the starting plumes occurred in four characteristic stages: Stage 1 is the plume acceleration stage, followed by stage 2 which corresponds to the formation of the head of the plume which grows spatially. Stage 3 is when the plume head is fully formed and the flow transitions to quasi-steady-state behavior. The final stage is the fully developed plume. The identification of the four-stage development of the plume in the neutral environment is the first step in studying the turbulent heated and buoyant plumes development in order to characterize realistic plumes and to quantify the extent of mixing at each of these stages. This work has important contributions to fundamental fluid dynamics of buoyant plumes with implications on forecasting the plume trajectory of smoke, wildland fire, and volcanic plumes.

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