2007 年 73 巻 732 号 p. 1647-1654
To investigate the effect of drag-reducing surfactant on typical elementary motions in turbulent flows, direct numerical simulation was carried out for a pair of streamwise vortices and a single low-speed streak. The surfactant solution was represented by a modified Bird-Carreau model. In surfactant solution, the streamwise vortices were inhibited immediately. On the other hand, the low-speed streak was less affected. Secondary streamwise vortices generated by low-speed streak were inhibited at downstream of surfactant solution. In such a sense, maintainance mechanism of low-speed streak was changed. In order to clarify the factor of modification of the elementary motions in turbulence, the energy budget was estimated. The inhibition of streamwise vortices resulted from strong viscous diffusion due to non-Newtonian effect. The influence of surfactant on the low-speed streak motion is mainly caused by the change in magnitude of energy redistribution. This is an indirect effect of streamwise vortices around a streak.