Vortex Filament Dynamics

Biot-Savart induced velocity field — vortex ring, leapfrogging, trefoil knot

Configuration

Biot-Savart Law

dv = (Γ/4π) dl × r̂ / r²

v(x) = Γ/4π ∮ (dl×(x−x')) / |x−x'|³

Vortex ring self-velocity:
V = (Γ/4πR)[ln(8R/δ) − ½]

Kelvin impulse: P = ρΓπR²ẑ

Vorticity ω = ∇×v
Helicity: H = ∫v·ω dV
(topological invariant!)
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