Abstract
Precession is the motion that the spin axis of a rotating object rotates about another axis. A precessing sphere generates and sustains turbulence of a confined fluid. Using particle image velocimetry, we investigate turbulent velocity fields on the equatorial plane of the precessing sphere. With the additions of cationic surfactant(CTAC) and counterion, sodium salicylate(NaSal), turbulence suppression is observed in a central region of the sphere. When themolar concentration of CTAC(C_D) is kept constant and that of NaSal(C_S) increases, in the range of C_S/C_D ≳ 1, turbulence is suppressed, while such a suppression is not observed for C_S/C_D = 0.5. For C_S/C_D ≳ 1, there are fully entangled threadlike micelles in the solution. Moreover, free salicylate ions exist and they promote reconnections of threadlike micelles. This may be the reason why turbulence suppression in a precessing sphere is sustained for a long time in the cases with rich free salicylate ions.
