(color online) Velocity distributions at different switching time. The different numbers stand for different interval time steps, for example, the number 100 means 100 (100×1 s). is the given translational velocity of the fluid boundary node where the outer normal direction of the particle is consistent with the particle movement direction, D is the particle length scale and υ is the kinematic viscosity. For Maxwellian, . v ⁰ is the fluid node velocities scaled by the average value of the fluid node velocities. is the normalised fluid nodes velocity distribution.