Appearance of gel-like shear-induced structures and flow modification in turbulent channel flow with dosing of dilute surfactant solution

The present study examined the experiment of surfactant solution dosing into a fully developed channel flow of wall turbulence from a permeable plate attached to one sidewall. To identify fluids of dosing and bulk flow in the channel, the fluorescent dye was added into the dosing fluid and so we were able to track the dosing fluid by planar laser-induced fluorescence (PLIF) measurement. From PLIF images, we found that, by dosing a dilute surfactant solution, gel-like shear-induced structures (gel-like SISs) appear near the dosing wall independently on a solution of the main flow. Upper parts of the gel-like SISs swing back and forth with time. The gel-like SISs behaved like as a solid block the flow near the dosing wall and result in a large drop in pressure. Additionally, dependences of the gel-like SISs on the dosing velocity, dosing time, and Reynolds number were investigated.