Article contents
On vortex-sheet evolution beyond singularity formation
Published online by Cambridge University Press: 30 November 2023
Abstract
We consider the evolution of a spatially periodic, perturbed vortex sheet for small times after the formation of a curvature singularity at time $t=t_c$ as demonstrated by Moore (Proc. R. Soc. Lond. A, vol. 365, issue 1720, 1979, pp. 105–119). The Moore analysis is extended to provide the small-amplitude, full-sheet structure at
$t=t_c$ for a general single-mode initial condition in terms of polylogarithmic functions, from which its asymptotic form near the singular point is determined. This defines an intermediate evolution problem for which the leading-order, and most singular, approximation is solved as a Taylor-series expansion in
$\tau = t-t_c$, where coefficients are calculated by repeated differentiation of the defining Birkhoff–Rott (BR) equation. The first few terms are in good agreement with numerical calculation based on the full-sheet solution. The series is summed, providing an analytic continuation which shows sheet rupture at circulation
$\varGamma =0^+$,
$\tau >0^+$, but with non-physical features owing to the absence of end-tip sheet roll up. This is corrected by constructing an inner solution with
$\varGamma < \tau$, as a perturbed similarity form with small parameter
$\tau ^{1/2}$. Numerical solutions of both the inner, nonlinear zeroth-order and first-order linear BR equations are obtained whose outer limits match the intermediate solution. The composite solution shows sheet tearing at
$\tau =0^+$ into two separate, rolled up algebraic spirals near the central singular point. Branch separation distance scales as
$\tau$ with a non-local,
$\tau ^{3/2}$ correction. Properties of the intermediate and inner solutions are discussed.
JFM classification
- Type
- JFM Papers
- Information
- Copyright
- © The Author(s), 2023. Published by Cambridge University Press
References
- 1
- Cited by