New omega vortex identification method

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SCIENCE CHINA Physics, Mechanics & Astronomy
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SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 59, Issue 8: 684711(2016) https://doi.org/10.1007/s11433-016-0022-6

New omega vortex identification method

ChaoQun Liu1,*, YiQian Wang1,2, Yong Yang1, ZhiWei Duan3
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  • ReceivedJan 13, 2016
  • AcceptedApr 19, 2016
  • PublishedJun 12, 2016
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Abstract

A new vortex identification criterion called W-method is proposed based on the ideas that vorticity overtakes deformation in vortex. The comparison with other vortex identification methods like Q-criterion and l2-method is conducted and the advantages of the new method can be summarized as follows: (1) the method is able to capture vortex well and very easy to perform; (2) the physical meaning of W is clear while the interpretations of iso-surface values of Q and l2 chosen to visualize vortices are obscure; (3) being different from Q and l2 iso-surface visualization which requires wildly various thresholds to capture the vortex structure properly, W is pretty universal and does not need much adjustment in different cases and the iso-surfaces of W=0.52 can always capture the vortices properly in all the cases at different time steps, which we investigated; (4) both strong and weak vortices can be captured well simultaneously while improper Q and l2 threshold may lead to strong vortex capture while weak vortices are lost or weak vortices are captured but strong vortices are smeared; (5) W=0.52 is a quantity to approximately define the vortex boundary. Note that, to calculate W, the length and velocity must be used in the non-dimensional form. From our direct numerical simulation, it is found that the vorticity direction is very different from the vortex rotation direction in general 3-D vortical flow, the Helmholtz velocity decomposition is reviewed and vorticity is proposed to be further decomposed to vortical vorticity and non-vortical vorticity.


Funded by

The simulation of MVG was originally supported by Air Force Office of Scientific Research supervised by Dr. John Schmisseur(FA9550-08-1-0201)


Acknowledgment

The direct numerical simulation data of the transitional boundary layer was supported by the Department of Mathematics at University of Texas at Arlington. This work is accomplished by using Code DNSUTA which was released by Dr. ChaoQun Liu at University of Texas at Arlington in 2009. The simulation of MVG was originally supported by Air Force Office of Scientific Research (Grant No. FA9550-08-1-0201) supervised by Dr. John Schmisseur and then the Department of Mathematics at University of Texas at Arlington. This work was accomplished by using Code LESUTA which was developed by Drs. Qin Li and ChaoQun Liu at University of Texas at Arlington. The authors are grateful to Texas Advanced Computing Center (TACC) for providing computation hours. YiQian Wang also would like to acknowledge the Chinese Scholarship Council (CSC) for financial support.


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