The contribution of active and inactive structures to the statistics of a turbulent pipe flow

The current study is a short follow-up to our most recent work (Stylianou et al., 2016), where among other things we have presented an effective criterion suitable for distinguishing large-scale coherent structures with low turbulent kinetic energy content (i.e. inactive structures) from their high energy counterparts (i.e. active structures). This criterion is based on the instantaneous values of the one-point turbulence Structure Tensors (Kassinos et al., 2001), which are effective in quantifying the different aspects of the coherent structures of turbulence. Same as in our previous work, here we perform Direct Numerical Simulation (DNS) of a fully developed turbulent pipe flow at bulk Reynolds number Reb=5300. Using simulation results, we accentuate the ability of this criterion to identify large-scale coherent structures and to differentiate between low energy and high energy content. Furthermore, based on this criterion we perform conditional averaging during the collection of statistics, which allows us to examine the contribution of the active and inactive structures to various large-scale and small-scale statistical quantities. Our results reveal that the characteristic trends in the turbulence statistics associated with the law of the wall, arise primarily due to contributions from the inactive structures. Moreover, in the log-law region both active and inactive structures contribute equally to the turbulence statistics.