Investigation of Various Structure Identification Methods and the Effects of Tabs on the Near Field of Round Jets

The effects of various combinations of vortex-generating tabs on the turbulence structures in the near-field of a round jet are investigated using LES simulation and flow visualization techniques. The visualization methods include stream-wise and non-streamwise vorticity, and a variety of methods that use the invariant of the velocity gradient tensor (the discriminant, Q value and the second eigenvalue condition). Integration of the LES data sets suggest that the structural changes as a result of introducing tabs is significant; however, the methods used to deduce these changes are not always consistent with one another. In some cases, one scheme will produce large amounts of background “noise” while others are less prone to this effect. It is concluded that qualitatively, the four tab case produces the greatest amount of small scale structure.