The boundary integral formulation of Stokes flows includes slender-body theory

Koens, Lyndon; Lauga, Eric

Abstract

The incompressible Stokes equations can classically be recast in a boundary integral (BI) representation, which provides a general method to solve low-Reynolds-number problems analytically and computationally. Alternatively, one can solve the Stokes equations by using an appropriate distribution of flow singularities of the right strength within the boundary, a method that is particularly useful to describe the dynamics of long slender objects for which the numerical implementation of the BI representation becomes cumbersome. While the BI approach is a mathematical consequence of the Stokes equations, the singularity method involves making judicious guesses that can only be justified a posteriori. In this paper, we use matched asymptotic expansions to derive an algebraically accurate slender-body theory directly from the BI representation able to handle arbitrary surface velocities and surface tractions. This expansion procedure leads to sets of uncoupled linear equations and to a single one-dimensional integral equation identical to that derived by Keller & Rubinow (J. Fluid Mech., vol. 75, 1976, p. 705) and Johnson (J. Fluid Mech., vol. 99, 1979, p. 411) using the singularity method. Hence, we show that it is a mathematical consequence of the BI approach that the leading-order flow around a slender body can be represented using a distribution of singularities along its centreline. Furthermore, when derived from either the single-layer or the double-layer modified BI representation, general slender solutions are only possible in certain types of flow, in accordance with the limitations of these representations.

Citation

Koens, L., & Lauga, E. (2018). The boundary integral formulation of Stokes flows includes slender-body theory. Journal of Fluid Mechanics, 850, Article R1. https://doi.org/10.1017/jfm.2018.483

• Journal Article Type: Article
• Acceptance Date: Oct 9, 2018
• Online Publication Date: Jul 2, 2018
• Publication Date: Sep 10, 2018
• Deposit Date: Jan 25, 2022
• Journal: Journal of Fluid Mechanics
• Print ISSN: 0022-1120
• Electronic ISSN: 1469-7645
• Publisher: Cambridge University Press
• Peer Reviewed: Peer Reviewed
• Volume: 850
• Article Number: R1
• DOI: https://doi.org/10.1017/jfm.2018.483
• Public URL: https://hull-repository.worktribe.com/output/3916599