LAUSR

Abstract The vortex identification methods are mutually compared on the basis of extracting coherent vortices and isolating incoherent regions from a filtered turbulent velocity field. Those identification schemes are the high rotation Q − criterion, the second large eigen value λ 2 − definition, the Δ − method, the vorticity magnitude |ω| and the new omega identification method ωnew. The velocity field of a forced homogeneous isotropic turbulent flow is obtained by simulating the lattice Boltzmann method (LBM) in a periodical box with resolutions of 1283 and 2563, respectively. The anisotropic diffusion model (ADM) is used to filter the velocity field into coherent and incoherent parts and finally the four identification methods are applied to identify the organized vortices as well as the noisy regions. The probability distribution functions (PDFs), the joint PDFs (JPDFs) and the spectrum of the extracted fields for the different identification methods are examined in details. Results show that the JPDFs have different shapes in the coherent cases, for example, the ( λ 2 − Δ ) and ( Q − Δ )-JPDFs for the non-filtered and coherent fields show an ellipse-like shape where the large axis is found in the Δ direction. The ( | ω | − Δ )-JPDFs for the non-filtered and coherent fields show a half circle - like shape. The ( | ω | − Q )-JPDFs for the non - filtered and coherent fields inclined towards the positive direction of Q and it is longer at higher values of |ω|. The ( | ω | − λ 2 )-JPDFs for the non-filtered and coherent fields inclined towards the negative values of λ2 and it is also longer for high values of |ω|. The incoherent JPDFs for the Δ method with other identification methods are found constant and their maximum existence are mostly found for moderate values of Q and λ2 at different values of Δ. However, the incoherent JPDFs ( | ω | − Q ) and ( | ω | − λ 2 ) are almost similar and the incoherent JPDF for ( λ 2 − Q ) is different, where most overlapping regions are found at negative values of Q and positive values of λ2. There is a tendency to have a universal JPDFs between the different identification methods where the same JPDF shapes can be observed in the 1283 and 2563 cases.