case of $A_x=A_z=3.0$ is considered. (c-f) Contours of the streamwise velocity in the $x$-$z$ cut plane at $y=-0.5$. Time instants $t=200$, 400, 550 and 1070 for the $A_x=A_z=3.0$ case are shown. Flow is from left to right.](Fig5a.pdf "fig:"){width="90.00000%"} ![\[fig:forcing\_amplitudes\] (a) The effect of the forcing amplitude on the generation of bands at $Re=750$. The kinetic energy of the disturbances with respect to the parabola, integrated in the whole channel, is plotted. $A_x$ and $A_z$ denote the amplitude in the streamwise and spanwise directions, respectively. (b) The forces are switched off at $t=550$ and the following development of the flow is plotted as a thin red line. The case of $A_x=A_z=3.0$ is considered. (c-f) Contours of the streamwise velocity in the $x$-$z$ cut plane at $y=-0.5$. Time instants $t=200$, 400, 550 and 1070 for the $A_x=A_z=3.0$ case are shown. Flow is from left to right.](Fig5b.pdf "fig:"){width="99.00000%"}

Firstly, we investigate the effects of the parameter $A$, i.e., the amplitude of the force. In order to mimic a noisy flow [[and to speed up the transition process]{}]{}, the flow is initialised with a turbulent velocity field simulated at $Re=1500$, [[with the perturbations with respect to the parabola being]{}]{} scaled by a factor of 