Abstract
Direct numerical simulations (DNS) of turbulent channel flow were performed in order to investigate the turbulence structures in fully developed wall turbulence of viscoelastic fluid. As a result, the simulations reproduced turbulent flow with drag reduction, and the modulation of the wall turbulence could be identified in comparison with that of Newtonian fluid. For example, the size of velocity streaks as well as the spanwise spacing of the streaks of viscoelastic fluid was larger than those of Newtonian fluid. In contrast, quasi-streamwise vortices weakened. In addition, a normalization method based on a newly defined friction velocity was proposed, so that the spatial scale of the turbulence structures of viscoelastic fluid could be normalized corresponding to that of Newtonian fluid, according to the scale analysis from a viewpoint of instantaneous structures and turbulence statistics. Therefore, by using the normalization method, we can observe universally the spatial features of turbulence structures of viscoelastic fluid.
