Advanced numerical modelling of the atomization process: application to an aeronautical injection system
Creators: name: Ferrando, Diego
Publisher: name: Zenodo
Year: 2023

description: The combustion inside of aircraft gas turbines is highly affected by fuel injection and atomization.<br> Reaching smaller droplets leads into a cleaner and faster combustion since the<br> evaporation takes place earlier, hence, promoting a good mixing. Thus, study the performance<br> of aeronautical atomizer is of high importance to understand the physical phenomena that<br> drive spray characteristics. On experimental campaigns, measurements such as the drop size<br> distribution and mean velocity of the droplets can be performed. However, due to the complex<br> geometries of atomizers and limitations of the current experimental techniques, early stage of<br> the atomization process is difficult to characterise. Numerical modelling play a role at this<br> level to enforce our description of such multiphase flows. On the last years, numerical studies<br> of aeronautical injectors have been carried out to model the flow inside the atomizer with<br> the goal to recover experimental measurements. Nevertheless, other difficulties are found on<br> numerical modelling such as the computational time and resources required.<br> On this work, a methodology applicable for numerical modelling of an aircraft atomizer is<br> proposed. In particular, an airblast prefilming atomizer, representative of gas-turbine injection<br> systems, is studied. Since performing one single simulation able to recover the whole injection<br> system is not possible due to the high amount of computational resources, a workflow has<br> been proposed that considers a succession of complementary simulations. This multi-simulation,<br> multi-scale approach allows eventually to study the essential features of the injection system.<br> The atomizer studied belongs to the CHAiRLIFT project within the Clean Sky 2 project.<br> Within this project, the aim of this work is to characterize the spray by calculating the drop<br> size distribution and the velocity of the droplets that can be used for further combustion<br> characterization. Since the atomization simulation is limited to the early stage of injection, a<br> recently proposed analysis is applied and developed further to give a more complete definition<br> of the spray. This analysis is based on the surface interface density SIGMA and the curvature k to<br> predict the joint number distribution of droplets at a given diameter and velocity.<br> In addition, since the CHAIRLIFT injection system requires a swirl injector to initiate the<br> internal liquid film and also because swirl injections are commonly used in gas-turbine systems,<br> this work includes also a simplex swirl injector. An injector applied on an academic project<br> dedicated to gas turbine spray flame is studied. The internal geometry of this Danfos swirl<br> injector is unknown. Thus, the internal geometry has been measured by several measurement<br> techniques and the computational geometry has been reconstructed. Modelling this kind of<br> injector is not straightforward due to the large range of scale to be considered, hence, a<br> two-simulation coupling has been proposed to overcome the difficulties of this simulation.<br> Results have been validated with the comparison with previous experimental campaigns. Finally,<br> the new analysis has been also applied to determine the spray size distribution at the early<br> stage of the atomization process and compare it to experimental measurements obtained further<br> downstream.