Engineering Method And Numerical Simulation Research Of Washing Inerting Process In Civil Aircraft Fuel Tank

With the advantages of high reliability, low cost of the life-cycle operation and few logistical requirements, the aircraft fuel tank inerting technology based on onboard inert gas generation system (OBIGGS) has become the civil aircraft fuel tank explosion-proof technology recommend by Federal Aviation Administration (FAA). Along with the launch of the major project of large aircraft, the research of civil aircraft fuel tank inerting technology has started. Under this circumstance, the research of engineering method and numerical simulation of washing inerting process in civil aircraft fuel tank was carried on in this thesis.On the basis of reading a large amount of relevant literature, the engineering models for single bay with or without oxygen evolution and multi-bay washing inerting process were deduced and developed in this thesis. And an easy-used engineering software with friendly interface of aircraft fuel tank inerting was developed with the help of Delphi7in this thesis. A contrastive calculation on single bay with and without oxygen evolution was made by applying the software. And, calculations on the multi-bay fuel tank inerting process in different air flow patterns were made as well.There are very few references on simulating the aircraft fuel tank inerting flow use the computational fluid dynamics (CFD) method at home and abroad. So, the CFD numerical simulation technology of fuel tank inerting was studied in this thesis. According to the characteristic of fuel tank inerting process, a basic CFD method was developed. With the single bay rectangular fuel tank and Boeing747center wing tank (CWT) from the FAA literature as the objects of the research, the numerical simulation method for single bay and multi-bay fuel tank was studied and analyzed respectively. The correctness and feasibility of the CFD method was verified by comparing the inerting results from numerical simulation with the results of engineering model and the test data from foreign literature. The CFD simulation results of the single bay fuel tank showed that:when the oxygen concentration of nitrogen-enriched air (NEA) is the same, the larger flow rate let the oxygen concentration of the ullage reduce faster, but the amount of NEA required to intert the ullage to12%oxygen concentration is equal. As for NEA of any oxygen concentration, there is a one-to-one relationship between the tank inerting ratio and VTE. The different position of NEA distribution nozzle and vents nearly has no influence on the average oxygen concentration, but it has an influence on the contours of oxygen concentration. Additional, the CFD results of the multi-bay fuel tank showed that:during the inerting process, the oxygen concentration differs greatly from bay to bay, while, the oxygen concentration distribution in individual bay is tending to be even and the outflow oxygen concentration of one bay is approximately equal to the average oxygen concentration of that bay. If the vents are placed symmetrically to the inlet of NEA, the flow rates can be weighted based on the cross-section flow areas; while, if the vents are placed unsymmetrically to the inlet of NEA, the flow pattern will be relatively complex.This thesis can provide reference for the study and design of civil aircraft fuel tank inerting system.