Fig. 4. S-shaped form of the dimensionless velocity (U_in/U_o, continuous line) approximating the rate of acceleration of the far-field flow approaching a flicking flagellum as a function of dimensionless time, t^* (tU_o/d_f). (In the calculations the flagellum is fixed and the flow accelerates past it.) Also shown is the dimensionless distance (x_f/d_f, broken line) traveled by the approaching flow in units of the flagellum diameter. For the conditions of interest in this work, U_o=8.63x10^–2 m s^–1 and d_f=5x10^–4 m.