The Propulsion Test Facility of the TU Braunschweig is capable of investigating future jet engine intakes and fan aerodynamics to a high level of detail. A goal of this facility is the examination of coupled fan-intake-interactions which is not possible in any existing test bench around the world. Before doing research on these interactions, it is important to undergo proper studies of isolated aspirated intakes and fans under varying operating conditions (design and off-design). Therefore comparable result of the well-known LARA nacelle to existing experimental and numerical data has been generated for a first validation purpose. Therefore, comparable studies have been conducted with the LARA nacelle, to that of experimental and numerical investigations performed in the early 1990s at the ONERA F1 wind tunnel (mention reference), in order to generate results for validation. The first results of the validation experiment show differences in peak Mach number between the ONERA F1 and PTF experimental data for identical boundary conditions based on Mach number and crosswind. To investigate this further, a comprehensive numerical study has been carried out. It was inferred that the discrepancy was mainly caused by the Reynolds number effect within the PTF environment and its sensitivity to the inlet flow angle distribution with regard to angle of attack for crosswind. Within the validation test campaign, the experimental investigations showed a separation and reattachment hysteresis, which was identified when crosswind as well as nacelle mass flow had been increased or decreased to set up the different operating points. This phenomenon has still no established theoretical basis for understanding the aerodynamic behaviour. Overall, the applicability of conventional RANS models is shown. Additionally, the sensitivity to the aforementioned boundary conditions and the numerical reproducibility of the hysteresis phenomenon are discussed and compared to new experimental data in detail.

The "Technische Universität Braunschweig" has commissioned a Propulsion Test Facility (PTF) for aspirated intake models of jet engines under off-design point conditions. For the commissioning of the unique facility, an aspirated intake test campaign has been carried out. Aim of the campaign was to compare the measured data in the PTF to numerical results and experimental data, which have already been measured in another test facility in the past using the same intake geometry. For the tests the Laminar Flow Reynolds Action (LARA) nacelle has been chosen. The LARA intake has been built and tested in the early 1990s at the "ONERA F1" wind tunnel during the work on hybrid laminar flow technology. At TU Braunschweig an Aspirated-Intake-Rig (ASI-Rig) with an in-house designed fan stage was worked out, whose fan is located far enough downstream to avoid interaction with the nacelle. For the results, the static pressure distribution at the inner and outer contour of the nacelle lip and the velocity distribution in the fan face during pure crosswind conditions have been compared and analysed. As seen in the results, the PTF pressure distribution at the lip is in good agreement with the numerical and the experimental data from the ONERA. Of particular note is the deviation between the achieved peak Mach number between the two experimental setups, analysed at the 0 • /180 • and 90 • section, which can be explained by the Reynolds number effect.

Even with different energy storage systems and power technologies of future aircraft, the thrust performance will be implemented with propulsors. In this context, the off-design nacelle behaviour – in particular for pure crosswind tests – becomes increasingly important especially for ultra-short nacelle designs due to their supposed drag and weight benefits [Peters and Rose (2015)]. In the upcoming years, several experimental tests at the Propulsion Test Facility (PTF) in Braunschweig are planned, to investigate the intake performance for different scale sizes and aspirated/powered test setups. As a starting point, two axisymmetric nacelles differing in intake length were designed and optimized at a representative full-scale fan diameter using an intuitive class/shape transformation based parametrization. The length was varied between L/D = 0.49 (classical design) and L/D = 0.36 (short design) with a minimum cruise drag design objective. The work flow of the optimization algorithm and nacelle parameter trends analysis are presented. Both intakes are scaled down to the testing rig’s diameter for the off-design analysis and a numerical setup and mesh density study are conducted. Through a detailed analysis of crosswind and scaling effects on the intake aerodynamics, the full-scale designs are modified to deliver a similar distortion behaviour for both designs by adapting the contraction ratio of the intakes. As a preparation for the upcoming tests, the numerical results of the local lip aerodynamics were analyzed for both intake designs showing, inter alia, that a decrease of the intake length increases the aerodynamic loading at the throat for the windward section.