Flow enhancement of deformable self-driven objects by countercurrent

We report numerical simulations of the mixed flows of two groups of deformable self-driven objects. The objects belonging to the group A (B) have drift coefficient D=DA (DB), where a positive (negative) value of D denotes the rightward (leftward) driving force. For co-current flows (DA,DB>0), the result is rather intuitive: the net flow of one group (QA) increases if the driving force of the other group is stronger than its own driving force (i.e., DB>DA), and decreases otherwise (DB