Abstract
Our aim is concerned with clustering or grouping of quasi-streamwise vortices. A fact that quasi-streamwise vortices are not distributed homogeneously but intermittently populated in space in a wall layer, is shown at first by referring to a Direct Numerical Simulation(DNS)data for a channel flow. Then, Regeneration property of quasi-streamwise vortices is one of the crucially important possible mechanisms for this clustering is shown by a simplified non-dynamical simulation. Next, a wavelet decomposition of quasi-streamwise vortices in two scale-based groups is shown. The interaction between vortices of two groups indicates that individual quasi-streamwise vortices can not survive long without assistance of surrounding large scale structure which is adapted for them. Thus, it is pointed out that large scale structure around a cluster of vortices is an important coherent ctructure to be investigated more in detail.
