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Using a Navier-Stokes isotropic turbulent field numerically simulated(Biferale et al., Phys. Fluids (2005)), we show that the probability of havinga stretching-tilting larger than twice the local enstrophy is negligible. Byusing an anisotropic filter in the Fourier space we analyze these survivalstatistics when the large, the small inertial or the small inertial anddissipation scales are filtered out. The probability that the ratio (|{\omega}\dot U|/|{\omega}|^2) is higher than a given threshold is higher in theunfiltered isotropic field than in the fields where the large scales werefiltered out and is lower than in the fields were the small inertial anddissipative scales are filtered out. This is due to the suppression of compactstructures in the removed ranges. The partial removal of the background offilaments and sheets does not have a first order effect on these statistics.These results are discussed in the light of a hypothesized relation betweenvortical filaments, sheets and blobs. The study can be viewed as a test forthis idea and tries to highlight its limits. A qualitative relation in physicalspace and in Fourier space can be supposed to exist for blobs only. That is forthe near isotropic structures which are sufficiently described by a singlespatial scale and do not suffer from the disambiguation problem as filamentsand sheets do. Information is also given on the filtering effect on the anglesbetween the strain rate tensor eigenvectors and the vorticity: eigenvector 2reduces its alignment, while eigenvector 3 reduces its misalignment. Allfilters increase the gap between the most extensional eigenvalue and theintermediate one and the gap between this last and the contractile eigenvalue.When the large scales are missing, eigenvalue modulus 1 and 3 become nearlyequal, similar to the modulus of the related components of the enstrophyproduction.

Survival distribution of the stretching and tilting of vortical structures in isotropic turbulence. Anisotropic filtering analysis