Calibrating numerical simulations with macroscopic bacterial models

The swimming of microorganisms is typically studied using biological experiments and/or numerical simulations. However, numerical simulations of microorganisms are often not compared to precise measurements because of the difficulty of making microscopic measurements of forces and torques in biological experiments, which are typically ∼ 10 µm. Instead, our research group uses robotic models that are about 10 cm in size and match the Reynolds number of swimming microorganisms by using highly viscous silicone oil that is 100,000X more viscous than water. We can then measure the translational motion of the models and scale the results from our dynamically similar experiments to biologically relevant sizes. We have used other experiments to calibrate the method images for regularized Stokeslets and found excellent agreement between our data for both cylinders and helices. Previous results also confirmed the theory of Jeffrey and Onishi (1981) for the torque on a cylinder near a plane wall, as reported in Shindell et al., Fluids (2021). Our current work tests the theory of O’Neill (1964) for a sphere moving near a wall as another reference for establishing appropriate parameters for Stokes flow simulations.