Computational fluid dynamics simulations of airflow through the nasal passages of rhinolophoid bats

The nasal passages of bats that emit their echolocation call through their nostrils have adapted for sound emission as well as standard respiratory and olfactory functions. Rhinolophids, hipposiderids and rhinonycterids all use a high duty cycle (HDC) echolocation strategy. In this study we used computational fluid dynamics (CFD) to simulate airflow through models of the nasal passages of 12 members of Rhinolophoidea, with the aim of gaining a greater insight into how differences in nasal passage anatomy and echolocation strategy influence airflow. We also aimed to gain greater insight into the function of the unique strands housed in the rhinolophid nasal passage, by comparing models with the strands intact and digitally removed. We found that nasal passage anatomy (e.g., the presence or lack of an ethmoturbinal I projecting into the rostral part of the nasal chamber), not echolocation strategy (HDC vs. low duty cycle) appeared to influence simulated airflow patterns and rates. Further, our results revealed digital removal of the unique strands within the nasal passages of the rhinolophids resulted in a reduction in the overall pressure gradient across the nasal passage models and altered the airflow patterns. How this pressure gradient change influences either the functions of echolocation and/or respiration warrants further investigation.