Modelling of sonic jets for gas leak applications

Design of gas turbine packages is subjected to safety issues and the related guidelines are provided by ISO-21789. According to this code, the ventilation system shall guarantee a good and safe dilution in case of an unexpected gas leakage from components of the fuel gas system inside the enclosure. The evaluation of the dilution is commonly carried out by CFD simulations and the ISO-21789 indicates the criteria to evaluate the danger of a gas leak by estimating the cloud volume of the explosive mixture. To follow this prescription and to properly calculate the exact volume cloud, it is fundamental to accurately reproduce the fuel gas leak, which is always a supersonic jet of fuel gas into an air-ventilated domain. The main criticality is to simulate a supersonic jet into a complex domain such as the gas turbine package, considering the industrial goals in terms of accuracy and time constraints. The complexity is due to the geometry of the package and to the multiple locations where the leakage could occur. In such context, it is preferable to develop an advanced modeling of the phenomenon rather than simply improve the detail of the CFD, that could turn out to be unfeasible for industrial goals. For this reason, the authors present a series of simulations of under-expanded jets at high pressure ratios carried out to investigate the applicability of the sonic source approach to not-round jets.