An experimental investigation of the effect of fractal grids on the near and full field structure of a turbulent round jet

Abstract

This project involves the experimental analysis of a jet with different nozzle configurations. The first configuration being a classic round nozzle and the second is modified adding a "fractal grid" by modifying the flow behavior and turbulent parameters. Both cases will be analyzed by an optical method, PIV, which is able to solve the velocity vector of a flow measuring the displacement of the particles of the flow. These particles have been initially added to the flow through a seeder PIV method not only provides an analysis of the speed but turbulent fluctuations of the velocity, the Reynolds stress and vorticity in case 3D PIV is used. Measuring supersonic speeds or the fact that it is a non-intrusive optical technique explains the reason PIV it is one of the most common experimental technique for analyzing flows. Reynolds stress is the component of the total stress tensor obtained by averaging the Navier-Stokes equations that define our turbulent flow. Averaging these equations explains where the turbulent fluctuations come. The simulations carried out show a comparison between the two configurations for all the turbulent parameters depending on the different regions of interest. The aim of this thesis is to understand the mechanisms and parameters involved in a turbulent flow but also contribute to the research of the jet noise produced by under the all sized structures present in the flow. Moreover, the use of "fractal grid" is being common among large companies for mixing the steady and accelerated flow more efficiently, noise reduction and even reduce the fuel consumption due to its more efficient combustion.