Influence of Surfactant on the Elementary Motions in Turbulent Flow

Predicting Drag-Reducing Wall Turbulence of Surfactant Solution by Direct Numerical Simulation

“…In contrast, in the case of surfactant solution, we observe fewer vortices, meaning that the vortices have decayed. The DNS of a pair of vortices by Ohshima (19) also predicted this decay.…”

“…as the deviatoric stress tensor, where μ is the viscous coefficient and D i j is the deformation rate tensor. Following Ohshima (19) , for a surfactant solution we used the constitutive equation for generalized non-Newtonian viscous fluid,…”

“…The viscosity for 10 ≤γ ≤ 30 was interpolated linearly between the initial viscosity and plateau viscosity. Ohshima et al (19) used the parameters determined by Usui et al (4) for the modified Bird-Carreau model. However, because their model parameters were not suitable for flow fields in which the effect of drag reduction occurred at a low Reynolds number, we used parameters adjusted to reduce viscosity change as shown in Table 1.…”

“…It is well known, however, that streaky structures of velocity fluctuation and quasistreamwise vortices sustain and regenerate each other in fully developed wall turbulence, although the study by Ohshima et al (19) did not consider such fully developed turbulent flow. Therefore, these results have not been confirmed for practical wall turbulence.…”

“…In this study, we conducted DNS of turbulent channel flow of surfactant solution to study the non-Newtonian effect of the SIS on fully developed wall turbulence. We expressed the SIS effect of surfactant solution with a combination of the constitutive equation for generalized non-Newtonian viscous fluid and the modified Bird-Carreau model, as did Ohshima et al (19) . Consequently, we clarified the difference in wall turbulence of surfactant solution and Newtonian fluid by considering instantaneous turbulence structures, turbulence statistics and energy transportation.…”