A) Gas velocity along a line in the three-dimensional simulation, which runs from the star through the opening of the bubble (as exemplified in Fig. 3). Plotted are the velocity profiles at different times t. The star is located at the dotted line. The sharp increase of the velocity close to the ionization front at t = 1 Myr and t = 3 Myr are turbulent motions induced by the finite grid of the simulation. Velocities of the gas with respect to the star range from v_f = 5 to v_f = 20 km s^-1. B) Kinetic energy E_k contained in the three-dimensional simulation (top panel) and fractional distribution of E_k (bottom panel). We separate E_k located into the neutral gas (green), the ionized gas (purple) and their total (black line), which are further divided into the subsonic (dashed) and the supersonic (dotted) part of each component.