A revision on low viscosity Rayleigh capillary jet breakup

The average Rayleigh capillary breakup length of a cylindrical Newtonian viscous liquid jet moving with homogeneous velocity $\hat{U}$ (negligible external forces) must be determined by the selection of normal modes with time-independent amplitude and wavelength. Invariant modes (IMs) with both positive and negative group and phase velocities exist in ample ranges of the parameter domain (Weber and Ohnesorge), which explains (i) the self-sustained average breakup length (long-term resonance), and (ii) the governing role on breakup of both spatial growth rate and wave number of the dominant positive group velocity IM. Published low viscosity experimental results confirm our proposal.