Respiratory airflow driven by propagative collapse in insect tracheae*

Insect respiratory systems are highly effective at transporting respiratory gases at the microscale, but their mechanisms of flow production are not well understood. Rhythmic tracheal compression (RTC), a gas exchange pattern that has been identified in multiple insect taxa, is characterized by the periodic compression and reinflation of parts of the tracheal system, creating advective flows that enhance transport. Synchrotron X-ray imaging has provided the precise kinematics of tracheal compression during RTC in several insects. Two types of tube collapse have been observed in tracheal pathways: propagating, with the collapse partially directed along the tracheal axis, and non-propagating. While multi-site, non-propagating collapse phenomena have been studied and modeled extensively, propagative collapse is less explored. Here, building on a previous theoretical model (Aboelkassem, Phys. Fluids, 2019) we study propagative collapse using three-dimensional finite volume simulations in idealized and in realistic tracheal geometries, with physiological collapse kinematics obtained from synchrotron X-ray imaging. The simulation results suggest that propagative collapses alone can induce net unidirectional flows in insect tracheae. Mimicking propagative collapse and other robust, decentralized insect respiratory actuation and control mechanisms in microfluidic devices may lead to improved performance.