Concept development of tank mounts for the integration of liquid hydrogen Tanks into aircraft structure supported by analytical and numerical means

Kurzfassung

The integration of hydrogen storage into the aircraft structure is vital to realize future clean aviation with hydrogen as energy carrier. For aircraft with ranges above regional that make up about 94% of CO2 emissions in the passenger transportation sector, large liquid hydrogen tanks are required that will be non-integral in the first developments. In aviation, tanks with cryogenic liquid hydrogen cooled down to -253 °C are used to achieve the highest possible volumetric efficiency. These non-integral tanks dictate the need of structural attachments between tank and fuselage. This master’s thesis links the mechanical and thermal challenges regarding load and heat transfer between the fuselage and the insulated tank. With regards to existing concepts from different applications and the derived boundary conditions on an aircraft, requirements for a tank suspension system are created. Based on these requirements, four concepts are developed and preliminarily sized. A metallic concept with a cylindrical mount shape was found to be most suitable to fulfill the determined requirements. The glass fiber composite version provides about three times higher thermal resistance. It was concluded, though, that the thermal loads do not present as big as an issue as expected. During standard operation a small temperature delta of merely 2 K was determined between the outer tank wall and the ambient temperature. The thermal resistance becomes more prominent in case of a vacuum break and a loss of insulation. With the chosen tank mounts, a fuselage temperature of 211 K during vacuum break at flight altitude is computed. As no limiting factor regarding a minimal fuselage temperature was found, this is seen as not critical. The challenge of the mechanical loads next to the general load definition is found to be the load inducement into the thin outer tank walls. Using reinforced joint areas of the outer vessel components to transfer the loads between wall and mount is found to be most suitable. As the cylindrical tank mounts provide a high thermal resistance geometrically, numerous mounts can be placed circumferentially around the tank to enhance the load distribution among the tank wall. A substantial challenge of the tank integration of non-integral tanks is the removability and accessibility for maintenance and tank exchange. Even though, the tank must only be exchanged three to four times in the aircraft’s lifespan, constructive measures for fuselage break points are to be implemented. A vertical exchange of the tanks is preferred regarding the access to the tank mounts. One suspension system has been developed with the focus on easy assembly and exchangeability, next to the mechanical and thermal requirements. The form-fitting mount shows a high volumetric efficiency and can be fixed through minimal installation patches in the fuselage skin but provides insufficient thermal resistance in a metallic configuration. Further research is required concerning the thermal deformation of the tank and the load transfer to the airframe. Here, replacing two conventional frames per tank with reinforced bulkheads are recommended.