Calibrating numerical models of spherical bacteria using macroscopic experiments

Biological experiments and numerical simulations are the most common methods of studying the swimming of microorganisms. However, biological measurements used to calibrate numerical simulations generally have large uncertainties. The Trinity-Centre Collaboration uses dynamically similar, macroscopic low Reynolds Number experiments to precisely calibrate the method of regularized Stokeslets (MRS) and the method of images for regularized Stokeslets (MIRS) to extract quantitatively accurate values for the forces and torques on a bacterial model moving near a boundary. We previously produced calibration data and optimal computational parameters for cylinders and helices (Shindell et al., Fluids, 2021). Our latest experiments measure the drag and torque on spheres moving parallel and perpendicular to boundaries. These data confirm, for the first time, the theory of Lee and Leal (1980) for the forces and torques present on a rotating and translating sphere near a plane wall. We have also developed an open-source MATLAB APP that calculates theoretical values for other researchers. The comparison among experimental measurements, theory, and optimized MIRS simulations shows excellent agreement.