Effects of hydrodynamic slip and taenidial structure in insect tracheal flows

Insects have evolved respiratory systems that transport air inside complex microscale tracheal networks in a highly efficient way, as evidenced by the fact that their metabolic range is the highest in the animal kingdom. This exceptional range has been attributed to their unique respiratory systems, which carry oxygen directly to the cells. Insect respiratory flows are characterized by low Reynolds numbers (~0.1), but the Knudsen numbers in insect tracheae span the continuum, slip, and transitional regimes (~0.0001-1). In this work, we investigate the effects of hydrodynamic slip and fine-scale internal tracheal morphology in intratracheal flows in insects in silico. We hypothesize that the helical taenidial structures found on the inner wall of the tracheal tubes determine the structure of the flow field near the wall and play a vital role in transport. We have closely reproduced the internal morphology of the tracheal tubes of the American cockroach, Periplaneta americana, in our computational geometry. To investigate this hypothesis, we performed a series of simulations using the-open source CFD toolbox, OpenFOAM at a Reynolds number of 0.1. We find that the taenidia significantly affect the flow structure and characterize their contribution.