Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

The Role of the Double Layer Potential in Regularized Stokeslet Models of Self-Propulsion

Version 1 : Received: 20 September 2021 / Approved: 23 September 2021 / Online: 23 September 2021 (11:02:27 CEST)

A peer-reviewed article of this Preprint also exists.

Smith, D.J.; Gallagher, M.T.; Schuech, R.; Montenegro-Johnson, T.D. The Role of the Double-Layer Potential in Regularised Stokeslet Models of Self-Propulsion. Fluids 2021, 6, 411. Smith, D.J.; Gallagher, M.T.; Schuech, R.; Montenegro-Johnson, T.D. The Role of the Double-Layer Potential in Regularised Stokeslet Models of Self-Propulsion. Fluids 2021, 6, 411.

Journal reference: Fluids 2021, 6, 411
DOI: 10.3390/fluids6110411

Abstract

The method of regularized stokeslets is widely-used to model microscale biological propulsion. The method is usually implemented with only the single layer potential, with the double layer potential being neglected, despite this formulation often not being justified a priori due to non-rigid surface deformation. We describe a meshless approach enabling inclusion of the double layer which is applied to several Stokes flow problems in which neglect of the double layer is not strictly valid: the drag on a spherical droplet with partial slip boundary condition, swimming velocity and rate of working of a force-free spherical squirmer, and trajectory, swimmer-generated flow and rate of working of undulatory swimmers of varying slenderness. The resistance problem is solved accurately with modest discretization on a notebook computer with the inclusion of the double layer ranging from no-slip to free slip limits; neglect of the double layer potential results in up to 24% error, confirming the importance of the double layer in applications such as nanofluidics, in which partial slip may occur. The squirming swimmer problem is also solved for both velocity and rate of working to within a few percent error when the double layer potential is included, but the error in the rate of working is above 250% when the double layer is neglected. The undulating swimmer problem by contrast produces a very similar value of the velocity and rate of working for both slender and non-slender swimmers, whether or not the double layer is included, which may be due to the deformation’s `locally rigid body’ nature, providing empirical evidence that its neglect may be reasonable in many problems of interest. Inclusion of the double layer enables us to confirm robustly that slenderness provides major advantages in efficient motility despite minimal qualitative changes to the flow field and force distribution.

Keywords

Stokes flow; propulsion; swimming; regularized stokeslets; double-layer; squirmer; undulating swimmer

Subject

MATHEMATICS & COMPUTER SCIENCE, Computational Mathematics

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