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Article

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

1
School of Mathematics, University of Birmingham, Birmingham B5 7EG, UK
2
Centre for Systems Modelling and Quantitative Biomedicine, University of Birmingham, Birmingham B5 7EG, UK
3
School of Science and Engineering, Tulane University, New Orleans, LA 70118, USA
*
Author to whom correspondence should be addressed.
Academic Editors: Sarah D. Olson and Laura A. Miller
Fluids 2021, 6(11), 411; https://doi.org/10.3390/fluids6110411
Received: 20 September 2021 / Revised: 2 November 2021 / Accepted: 9 November 2021 / Published: 13 November 2021
The method of regularised stokeslets is widely used to model microscale biological propulsion. The method is usually implemented with only the single-layer potential, the double-layer potential being neglected, despite this formulation often not being justified a priori due to nonrigid surface deformation. We describe a meshless approach enabling the 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 discretisation on a notebook computer with the inclusion of the double layer ranging from no-slip to free-slip limits; the 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 small 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 nonslender 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. The 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. View Full-Text
Keywords: Stokes flow; propulsion; swimming; regularised stokeslets; double-layer; squirmer; undulating swimmer Stokes flow; propulsion; swimming; regularised stokeslets; double-layer; squirmer; undulating swimmer
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MDPI and ACS Style

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. https://doi.org/10.3390/fluids6110411

AMA Style

Smith DJ, Gallagher MT, Schuech R, Montenegro-Johnson TD. The Role of the Double-Layer Potential in Regularised Stokeslet Models of Self-Propulsion. Fluids. 2021; 6(11):411. https://doi.org/10.3390/fluids6110411

Chicago/Turabian Style

Smith, David J., Meurig T. Gallagher, Rudi Schuech, and Thomas D. Montenegro-Johnson. 2021. "The Role of the Double-Layer Potential in Regularised Stokeslet Models of Self-Propulsion" Fluids 6, no. 11: 411. https://doi.org/10.3390/fluids6110411

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