Large Eddy Simulation of High-Density Ratio Jets

The aim of this project is the analysis of hydrogen jets by using a Large Eddy Simulation model in order to gain new insights into the fluid dynamic process of turbulent mixing. The investigation of such jets is a relevant subject for the development of new propulsion systems, to improve the performance and the efficiency of direct-injection engines and also for safety issues. The computations of hydrogen jets require accurate and robust computational tools. Hence, the use of a suitable code and high performance computing is mandatory to successfully carry out the simulations. The present work is carried out by means of an in-house code, named FLEDS. A significant issue when dealing with compressible free jets, especially with hydrogen jets, is the presence of sharp density gradients in the flow field, that cause non-physical spurious oscillations. In order to avoid these instabilities, an innovative localized Artificial Diffusivity Scheme has been implemented. The flow model has been assessed by comparing the numerical results with both theoretical considerations and experimental measurements. The influence of both high air/hydrogen density ratios and jet Mach numbers on the turbulent mixing and the spreading rate has been analyzed by means of FLEDS code. This is a major issue dealing with direct injection in combustion systems, since the efficiency of combustion and pollutant emissions are strictly related to the mixing of air and fuel in diffusive flames.