Computation of liquid jets BiGlobal spectrum via randomly perturbed numerical data

A data-driven approach to estimate the global spectrum of gravitational planar liquid jets is presented in this work. Numerical data have been obtained by means of the BASILISK code, based on the one-fluid formulation and the volume-of-fluid approach. The Dynamic Mode Decomposition (DMD) technique is applied to extract the underlying linear operator, considering random perturbations of the base flow. This methodology is applied to a two-dimensional configuration obtaining the BiGlobal spectrum. The analysis highlights that in supercritical regime (We > 1) the spectrum presents three branches: the upper and lower ones exhibit a purely sinuous behavior; the middle branch presents a predominant varicose component, increasing with the frequency. Experimental evidence shows that the varicose behavior is related to the rupture of the curtain.