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On vortex-sheet evolution beyond singularity formation
DOI:10.1017/jfm.2023.880.png)
摘要
En 中文
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 F = 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 Gamma < 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.
Keyword:
vortex dynamics
期刊
IF:
3.9
论文数:
2.0W
被引数:
9.4W
机构
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