Numerical simulation of the flow around larvae from the Drusinae subfamily*

Drusinae is a caddisfly subfamily whose larvae are found on the rock bed of small mountain creeks, being exposed to a turbulent flow. It is hypothesized that their head morphologies are related to the specific hydrodynamic properties of the different habitats of the members of the subfamily. For that reason, the flow past different larvae species of the subfamily is computed by LES to investigate the stresses acting on different larvae. The three-dimensional body shapes are constructed from micro-tomography data of the selected species. The flow parameters (Reynolds number) are selected based on spatio-temporally filtered velocity data measured during field excursions. The divergence-free synthetic eddy method (DFSEM) is employed to provide turbulent inlet conditions into a channel within which the larva sits on the wall. The simulations with the tested range of Reynolds numbers show differences in the total forces acting on each morphotype, supporting the hypothesis of preferred hydraulics between the different species. Furthermore, higher shear stresses were found on the head location for the larva that feeds by filtering the water. The higher velocity fluctuations may enhance the encounter rates of particles on their filtering devices.