Due to the high global demand for mobility and the associated increase in the number of commercial aircrafts, a significant reduction in fuel consumption in relation to European aviation emission targets is essential. Future aero engines are of major importance here. However, when developing more efficient engines, there is a trade-off between increasing propulsion efficiency while reducing the aerodynamic drag of the overall aircraft configuration. The enhancement of the propulsion efficiency can be achieved by increasing the bypass ratio and thus increasing the accelerated mass flow. As a result, this causes a geometric increase of the fan stage of the engine, which increases the proportion of the thrust generating secondary flow, which bypasses the core engine. At the same time, however, the overall drag of the aircraft increases due to the associated enlargement of the engine nacelle. On the other hand, drag-optimized engines should not cause any deterioration in efficiency.
Since the inlet diameter is determined directly by the required bypass ratio, a reduction in drag can be achieved primarily only by reducing the length and the lip or nose radius of the inlet. However, this requires a much deeper understanding of the interaction between inlet and the rotating fan itself, as both factors (length and nose radius) are essentially defined by the goal of a homogeneous and separation-free flow into the fan. For such novel intakes, an aerodynamically more aggressive design is needed, which will only be achievable with the knowledge of the detailed aerodynamic interaction.
Today’s development practice is based strongly on the interface between engine manufacturers (responsible for the fan) and aircraft manufacturers (responsible for the nacelle and thus the inlet) and the individual competitive situation. It results in the fact that combined experiments between inlet and fan won’t take place until very late within a concrete development project. Therefore, identified change requirements can lead to very high costs and delays. Preceding model experiments, on the other hand, take place rather separately for intake and fan.
The goal of this project is an experimental infrastructure and thus a possibility to investigate the described interaction between inlet and fan of UHBR engines in detail. For this purpose, a generic, i.e. universally applicable and modular structured, scaled device in the form of a, for the desired high bypass ratios representative, new generation fan-inlet-test-rig should be procured and built. Besides the necessary detailed investigations of the aerodynamic interaction, this will also allow a detailed study of the aeroelastic excitation. In addition to the described design of the test rig, modern metrology techniques such as imaging velocity- and deformation-measuring techniques (PIV and DIC) are going to be applied.
The obtained results are supposed to serve as the basis for the validation of the numerical methods used in research and development projects. Furthermore, new or enhanced aerodynamic and aeroelastic design guidelines for future engines for industrial use can be derived directly from the results. At the same time, the test rig also provides the framework for the experimental investigation and testing of new designs in industrial applications by providing a defined interface and reference data at the same time. Thus, new inlet designs for very different aircraft configurations can be experimentally examined and evaluated. Such a generic test facility for coupled fan-inlet investigations with aerodynamic or aeroelastic focus represents a completely new experimental environment in this form and today is neither available in the national nor in the international environment. At present, industrial companies have, if at all, only very limited test possibilities or access to application-oriented examinations, e.g. experiments without cross flow effects, as they are possible in the test facility at the Institute of Propulsion and Turbomachinery.