Dynamics of the free jets from nozzles of complex geometries

TL;DR

This study uses direct numerical simulation to analyze how different nozzle geometries affect jet dynamics, revealing that corner-induced rotation influences spreading and entrainment, with minimal impact from fractal scale effects.

Contribution

It demonstrates that jet rotation and spreading are primarily governed by corner geometry and vorticity, showing fractal nozzle scales do not significantly alter jet evolution compared to star-like nozzles.

Findings

Jet rotation velocity depends on corner angle.

Enhanced spreading linked to rotation induced by corners.

Fractal nozzle scales do not significantly affect jet development.

Abstract

The dynamics of the coherent structures in jets generated by nozzles of different shapes is analyzed through DNS at $Re_{D_e}=565$, by considering circular, square, fractal and star-like nozzles. The jets generated from orifices with corners, undergone a rotation proportional to the corner angular width: ${\theta}_{rotation}={\theta}_{corner}/2$. The velocity at which this rotation occurs is also affected by the angle of the corners, being faster for fractal and star-like nozzles which have small ${\theta}_{corner}$. Therefore it has been found that the velocity of the rotation is associated with enhanced spreading and entraining characteristics. The jet evolution and its rotation are dictated by the vorticity field and, in particular, by the positive and negative ${\omega}_x$ layers generated at each corner. The comparison between the fractal and the star-like jets at this Re, suggested that the effect of the smaller scales generated by the fractal nozzle does not play a role in the development of the jet, that evolves as the star-like one.