Pressure dynamics in the bottleneck flow of self-propelled particles

We present an experimental investigation of the pressure dynamics during the flow of self-propelled particles through narrow passages. When the ensemble is flowing, pressure fluctuates around a constant value that does not depend on the crowd size, suggesting that the orifice locally determines the dynamics in this scenario. On the contrary, when the system clogs, pressures are higher for larger crowd sizes, highlighting the importance of the whole collectivity in the process. Then, by correlating the pressure evolution with the exit time of the self-propelled particles, we discover that when a clog is resolved, pressure suddenly drops as a consequence of system reorganization. After this dramatic event, there is a sustained pressure growth over time that shows a square-root dependence, compatible with the structural aging that has been proposed to be behind the broad tail distributions of clogging times.