Dynamics of the free jets from nozzles of complex geometries

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.