Deforming Vortex Force Mapping for Undulating Swimmers

Xingxin Yang; Matteo Liguori; Vedang Joshi; Juan Li

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arXiv · 2609.00461

Deforming Vortex Force Mapping for Undulating Swimmers

Xingxin Yang·Matteo Liguori·Vedang Joshi·Juan Li

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Abstract

Undulatory propulsion is commonly interpreted through reactive added-mass loading associated with body kinematics and vortex-induced loading, but their relative contributions to the streamwise force have not been systematically quantified across swimming kinematics. Moreover, existing vortex-based descriptions do not resolve the signed spatial contribution of vortical flow to the streamwise force. We extend vortex force map (VFM) attribution to deforming bodies, demonstrated for prescribed two-dimensional undulating swimmers at $Re=5000$ across a range of Strouhal numbers and dimensionless wavelengths. The deforming-body VFM organises the streamwise force as a positive reactive added-mass scale with a signed vortex-pressure modification. Across the 80 cases, vortex pressure opposes the reactive contribution in 76 cases. Reference-configuration maps show that the near-body vortex-pressure contribution is consistently adverse, whereas the wake contribution changes sign across regimes and becomes favourable at high thrust. Net vortex-pressure assistance occurs only for the high-thrust anguilliform swimmer. A matched high-thrust pair further shows that the case with the higher peak downstream velocity has the smaller signed wake contribution, demonstrating that wake intensity alone does not determine its force effect.

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Xingxin Yang, Matteo Liguori, Vedang Joshi, Juan Li. 2026-08-31. Deforming Vortex Force Mapping for Undulating Swimmers. https://arxiv.org/abs/2609.00461

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