Spatial distribution of coherent structures in a self-similar axisymmetric turbulent wake

The coherent structures play a significantly important role in the spatial evolution of turbulent wakes. The spatial distribution and the organization of the coherent structures in a self-similar axisymmetric turbulent wake are numerically discussed by using the data from the previous simulation [Zhou and Vassilicos, Related self-similar statistics of the turbulent/non-turbulent interface and the turbulence dissipation, J. Fluid Mech. 821, 440 (2017).], in which it was found that the radial positions of the turbulent/nonturbulent (T/NT) interface at different downstream locations exhibits a self-similar form normalized by the wake width & delta;. The Liutex method is used to automatically identify the vortex core center and compute the direction of the vortex axis. The probability density functions (PDFs) of the radial distance of the vortex core center Rc at different streamwise locations can be superimposed on the same curve, and the PDFs of Rc scale with & delta;. There is a discernible preference for the vortex axis to be normal to the mean direction of the flow, and the PDFs of the polar angle & alpha; at different downstream locations collapse onto a single curve. The PDFs of the separation distance Rct between the T/NT interface and the nearest vortex core center are also self-similar and scale with & delta;. The averaged radial distance Rct is of the order of the Taylor microscale. The results reported in this work suggest that the coherent structures are orderly distributed and also regularly organized in a self-similar axisymmetric turbulent wake.