CFD analysis of dispersion of Halon 1301 from a Fire Extinguishing System in the engine nacelle of a medium-size helicopter

The object of this Master Thesis is to conduct a CFD simulation of Fire Extinguishing agent Halon 1301 (CBrF(3)) spreading into a medium-size helicopter engine nacelle in order to predict the efficiency of the Fire Extinguishing System (FES). CAD models of FES, engine and nacelle, the softwares licenses and technical support were all provided by Leonardo - Helicopters Division (LHD) (Cascina Costa) and it is the result of one year of cooperative effort due to the implicit difficulty of the case. The reason that lead the company to commission such a long trip to me are explained by the need of finding an alternative certification process to this type of systems installed on board of aircrafts and helicopters. In fact the Montreal Protocol established a limit on the use of Fire Extinguishing agent Halon 1301 due to its polluting effects. Several aternative agents have been tested in order to replace it. However, its use still is largely spread in aerospace world because of its efficiency in putting out fires. In fact, according to FAA Advisory Circular AC 20-100, to successfully extinguish a fire, the concentration of Halon 1301 must be greater than 6% by volume for a minimum of 0.5 seconds simultaneously on all sampling probes. The Fire Extinguisher System can be certificated if this requisite is proved by 12 tests taken in different flight and ambient conditions. If the requisite is not respected, the FES project has to be changed, with consequentially new tests and increaseas in the use of Halon and costs for the company. However, a CFD analysis of agent spreading inside the nacelle can be conducted prior to the tests, once the project is fully developed, in order to already know if the requisiste could not be respected and change the project until it is. Moreover, a further development could be that of directly certificate the FES from CFD simulation when the numeric methods will become enough accurate, so to prevent phisycal certification tests and respect the limit imposed by the Montreal Protocol. This work can be splitted into two macro-operations: the creation of a FES model through the Siemens Amesim software to provide the outlet conditions of the agent; these results are then used in the second part as boundary conditions for the CFD simulation of the agent spreading inside the nacelle through the Siemens Star-CCM+ software. In the end, the results obtained are compared to the tests evidences in order to validate the method. The difficuties of this approach were different: about the first part, the biggest difficulty was to find the way to integrate different models in Siemens Amesim in order to obtain the most accurate information, while the second part difficulty was to find the right set up of physic and solvers in order to stabilize the numerical method. To outocome these troubles, the support of Siemens experts was needed.