Transport and absolute negative mobility of inertial Brownian particles induced by harmonic force in steady laminar flows

Transport of inertial particles advected by a two-dimensional incompressible laminar flow is numerically investigated under the combined action of a time-periodic (harmonic) driving force, a constant bias force, and thermal noise. Through extensive numerical simulations, we demonstrate that the velocity–force relation of particles exhibits complex dynamical behaviors, and a counterintuitive phenomenon, referred to as absolute negative mobility, is observed. Notably, applying an appropriate harmonic force can lead to a drastic enhancement of absolute negative mobility, characterized by both a significant increase in the magnitude of the steady-state reverse velocity and a remarkable expansion of the parameter regime for this phenomenon. The results reveal that the inertial effects of particles in laminar flow induce a phase lag between the particle velocity and the applied harmonic force, which gives rise to an effective asymmetric potential landscape that directs particles to move against the bias force. We identify the optimal parameter regimes for absolute negative mobility via phase diagrams, providing a quantitative guide for practical applications in physics, chemistry, and biomedicine, such as the selective transport or sorting of cells, organelles, and biomolecules, as well as in targeted drug delivery.