New omega vortex identification method

• Published in: Science China. Physics, mechanics & astronomy Vol. 59; no. 8; pp. 56 - 64
• Main Authors: Liu, ChaoQun, Wang, YiQian, Yang, Yong, Duan, ZhiWei
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.08.2016; Springer Nature B.V
• Subjects: Astronomy; Classical and Continuum Physics; Criteria; Decomposition; Direct numerical simulation; Fluid flow; Identification methods; Observations and Techniques; Physics; Physics and Astronomy; Three dimensional flow; Vortices; Vorticity; 三维涡流; 旋涡结构; 欧米茄; 涡旋; 直接数值模拟; 识别准则; 识别方法; 速度分解; vortex; turbulence; vorticity; vortex identification
• ISSN: 1674-7348; 1869-1927
• DOI: 10.1007/s11433-016-0022-6

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 λ_2-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 λ_2 chosen to visualize vortices are obscure;（3）being different from Q and λ_2 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 λ_2 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.