Left with adiabatic boundary condition, right with structural influence (FSI)
DLR (CC BY-NC-ND 3.0).
Hydrogen as a primary energy carrier represents an important step on the way to CO2-free aviation. As a useful intermediate step, bivalent combustion systems (hydrogen and Sustainable Aviation Fuels, SAF) should drive the development of H2-capable engines and the spread of the necessary hydrogen infrastructure. Hydrogen/liquid combined cycle operation is especially challenging for the combustor and turbine, as staged combustion must be designed with two fuel lines. Combustion chamber and burner must be matched to minimise emissions and ensure operational stability. On the turbine side, mixed operation with new combustion chamber architecture needs a new development for increased efficiency with higher water content in the exhaust gas. The first turbine stage in an engine is located downstream of the combustion chamber, where high turbulence is generated. As a result, the boundary layers are almost completely turbulent. Together with the high exhaust gas temperature, the thermal load on the components is extreme. Cooling systems are used to counteract this. Even for kerosene-burning engines, the design of the cooling system has not been fully exhausted after decades, which means that components are sometimes cooled too much and sometimes too little. In the use of hydrogen, this problem is even more pronounced due to less experience.
Understanding turbulence and its migration through a turbine helps to improve the design of the cooling system and thus use cooling air effectively and increase the service life of components. For this purpose, extensive tests will be carried out at the turbine test rig of the DLR Institute of Propulsion Technology in Göttingen. Due to the accessibility of the rig and the space required by the measuring instruments, only a small part of the flow field can be measured. The turbulence behaviour is not completely recorded, which means that a simulation model of the turbine is necessary with which the turbulence migration can be recorded in the interaction of flow, rig structure and measurement technology at any point. To verify the calculations, the results are compared with measurements at discrete points.
Due to the thermal aspects, a coupled simulation of fluid and structure is essential to achieve the highest possible precision in the simulations. In addition, the size of the FE models must be taken into account, as the structure of the turbine is very complicated due to the complex cooling air supply systems. By comparing experiments and simulations, possible methods for improving the modelling and the measurement technology can also be developed. This will also further reduce the development times of new technologies in the future.