Global pressure fluctuations in numerical simulation of spatially developing jets

This paper addresses some issues related to the numerical simulation of the spatial evolution of perturbations in highly unstable submerged jets. It is confirmed that artificial conditions at the outflow boundary lead to the generation of spurious global pressure fluctuations that transfer perturbations to the inflow region and initiate the occurrence of global instability. Estimates and interpretations explaining the mechanism of this phenomenon are presented. It is shown that the qualitative behavior of the solution depends not only on the length of the computational domain, but also on its transverse size. In the course of nonlinear simulations, it was found that global pressure fluctuations are emitted from regions of nonlinearity into the surrounding space, where the nonlinear terms have a negligibly small amplitude. This effect makes it possible to predict the position of the nonlinearity boundary depending on the amplitude of inflow disturbances and the width of the computational domain. The results obtained in this work can be extended to other highly unstable spatially evolving flows.