TURBULENCE GENERATION OF ROUND SUBSONIC JETS WITH FRACTAL GRIDS

This experimental study compares the turbulent structure of two turbulent round jets issuing with different initial conditions: one turbulent jet generated without noticeable upstream disturbances while the other has a fractal grid located upstream of the jet orifice. Particle image velocimetry is used to measure the instantaneous 2-component-2-dimensional fluid velocity in the near and far field of these jets. The large number of statistically independent velocity fields acquired are used to determine first and second order statistics of the velocity, as well as two point correlations. This data was subsequently used to analyse the spatial development of the flow and its approach towards a self-similar state in the far field. The self-similar characteristics of these jets have been compared and used to characterise the large-scale coherent structures for each jet configuration.