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The scope of the present paper is to assess the potential of distributed propulsion for a regional aircraft regarding aero-propulsive efficiency. Several sensitivities such as the effect of wingtip propellers, thrust distribution, and shape modifications are investigated based on a configuration with 12 propulsors. Furthermore, an initial assessment of the high-lift performance is undertaken in order to estimate potential wing sizing effects. The performance of the main wing and the propellers are thereby equally considered with the required power being the overall performance indicator. The results indicate that distributed propulsion is not necessarily beneficial regarding the aero-propulsive efficiency in cruise flight. However, the use of wing tip propellers, optimization of the thrust distribution, and wing resizing effects lead to a reduction in required propulsive power by $$-2.9$$ - 2.9 to $$-3.3\,\%$$ - 3.3 % compared to a configuration with two propulsors. Adapting the leading edge to the local flow conditions did not show any substantial improvement in cruise configuration to date.

Forschung im Ingenieurwesen (2021). doi:10.1007/s10010-021-00452-3, Published by Springer, Berlin ; Heidelberg

The scope of this paper is to investigate and improve the aerodynamic properties of a propeller driven state-of-the-art active high-lift configuration in lateral motion. 3D RANS simulations of the landing configuration with circulation control and slipstream deflection under crosswind, and one engine inoperative (OEI) conditions were performed. The configuration shows directionally unstable behavior at small sideslip angles and high yawing moment production under OEI conditions. Flowfield analyses indicate that both can be attributed to wake-tail interference effects caused by slipstream–vortex interaction. The integration of tail fences at the rear of the fuselage leads to considerable improvements for both conditions.

The aerodynamic properties of a state-of-the-art short take-off and landing aircraft design with circulation control and slipstream deflection in landing configuration have been investigated via RANS simulations. The present paper summarizes the findings concerning one engine inoperative conditions (OEI), active control surface design, and ground effect. It is shown that the unfavorable aircraft’s aerodynamic characteristics under OEI conditions, including a degraded maximum lift coefficient and extraordinarily high yawing moments, can be improved via passive measures, such as nacelle strakes and tail fences. The resulting requirements for lateral control forces can be fulfilled by the use of circulation controlled rudder and ailerons. Simulations of the 3D configuration in ground proximity yield a beneficial effect on the lift coefficient despite contrary indications from 2D computations. Furthermore, the simulations show a significant pitch down tendency due to ground proximity.

Electric propulsion systems are considered as one possibility to reach the ambitious goals of the European Union’s Flightpath 2050 with regards to greenhouse gas emissions and noise. It has been claimed in several publications that Distributed Electric Propulsion (DEP) offers significant improvement in aerodynamic efficiency and thus a reduction in structural weight of the wing and noise emissions as well as additional degrees of freedom concerning flight control. To not outweigh those advantages by heavier drivetrains, the components within the electric propulsion system have to be extremely lightweight, efficient and reliable at the same time. The German nationally funded project SynergIE evaluates DEP for a 70 PAX regional reference aircaft with two (SE-2), six (DEP-6) and twelve (DEP-12) propulsion units with a turbo-electric drivetrain layout. This study aims to quantify the effect on the specific block fuel consumption for the different numbers of propulsors based on Top Level Aircraft Requirements (TLARs). The approach contains a coupled electric drivetrain system model which is based on physically derived, analytical models for each component linking specific subdomains, e.g., electromagnetics, structural mechanics and thermal analysis. A genetic algorithm is applied to optimise the key performance indicators (KPIs) of the electric system, before the results are fed back to the aircraft sizing process. It has been identified that constraints such as installation space or architectural decisions such as the number of propulsors have significant influence on the drivetrain weight and efficiency and interact with the whole aircraft sizing process, esp. with reference to nacelle weight and drag and thus the block fuel consumption. The study shows that the DEP-6 and DEP-12 project aircraft both have a potential of reducing the specific block fuel consumption by approx. 4.2 % and 5.8 % respectively in case of direct driven propellers, while for a geared-drive scenario a total reduction of up to 7.6 % in case of DEP-6 and 8.5 % in case of DEP-12 is possible, all compared to the direct-driven baseline (BSL) aircraft SE-2.

A modified actuator disk method based on blade element momentum theory is applied to an UHBR turbofan engine with the DLR TAU Code. The method is compared against RANS simulations with a common thermodynamic engine boundary condition and high-fidelity 360° uRANS simulations as well as RANS mixing-plane data from the design process of the engine conducted with the DLR flow solver TRACE. The input data of the actuator disk model comprise sectional lift and drag coefficients of the rotor and stator blades which are obtained by 2D RANS computations of the blade sections performed with the TAU Code. The boundary conditions for these 2D computations are derived from the aforementioned RANS mixing-plane results obtained during the design process of the investigated engine. Good agreement between the RANS actuator disk method and the uRANS results as well as the RANS mixing-plane data is observed. The actuator disk model is able to predict global engine performance data for different engine operating points. Detailed analysis shows that the actuator disk model is able to reproduce characteristic non-uniform inflow phenomena that could in the past only be modeled with uRANS computations. Additionally the model is capable to accurately predict the thrust distribution between rotor and stator. Therefore it is able to fill the gap between the currently used thermodynamic engine boundary condition and high-fidelity uRANS computations with only a minor increase in required computational resources.

The contribution gives an overview over a wide range of CFD simulations, which were performed in the course of the German collaborative research center 880 in order to investigate the aerodynamic properties of a complete turboprop powered transport aircraft in landing configuration with a circulation control high-lift system. The main purpose of the contribution is to highlight aerodynamic and flight mechanical aspects of the integration of lift augmentation technologies into the design of a short take-off and landing aircraft concept. In this context, the influence of engine nacelles and thrust on the stall behavior and the following improvements due to the use of a nacelle strake are discussed. Furthermore, static longitudinal and lateral stability as well as the dynamic longitudinal stability are investigated. While circulation control itself has a rather small impact on the stability, the impact of engine thrust in conjunction with circulation control is considerable. Additionally, the one engine inoperative case was simulated. For some flow and engine conditions, the resulting yawing moments are more than twice as high as the actual yawing moments due to asymmetric thrust.

The scope of this paper is to investigate and improve the aerodynamic properties of a propeller driven active high-lift configuration in lateral motion. Therefore, results of 3D RANS simulations of a landing configuration with circulation control and slipstream deflection under crosswind and one engine inoperative (OEI) conditions are discussed. The configuration shows directionally unstable behavior at small sideslip angles and high yawing moment production under OEI conditions. Flowfield analysis indicate that both can be attributed to wake-tail interference effects, caused by slipstream-vortex interaction. The integration of tail fences at the rear of the fuselage leads to considerable improvements under both conditions.

In this study, the aerodynamics of wings using an active high-lift system are investigated. The target is the flight mechanical description of the spanwise forces and resulting moments and the influence of the active high-lift system to their distribution. The high-lift system is a blown flap system divided into six segments per wing. Each segment is assumed to be individually controlled, so the system shall be used for aircraft control and system failure management. This work presents a flight mechanical sub-model for the simulation of flight dynamics, which has been derived from high-fidelity CFD results. An assessment of single-segment blowing system failures will be presented including recommendations for compensation of either lift or rolling moment loss. For this investigation, the compensation is required to act at the same wing side on which the failure appears. Thus, the potential for an increase of system reliability shall be proven. The results show that less performance investment in terms of pressurized air is necessary to compensate the rolling moment of a failing segment instead of its lift. However, large blowing performance increases for the remaining wing segments that occur for some of the failure cases.

The scope of this paper is to demonstrate the feasibility of a numerical evaluation of dynamic derivatives of a 3D high-lift configuration. Furthermore, the influence of active lift augmentation systems on the longitudinal dynamic derivatives shall be illustrated. Therefore, forced pitching and plunging motions at different boundary conditions were simulated. The investigation started with a comprehensive sensitivity study regarding algorithmic and configurational parameters on a representative 2D-model. The results show the impact of frequency, amplitude, flap deflection and blowing coefficient. Based on the preliminary 2D study, boundary conditions were selected for the simulation of the entire aircraft in landing configuration. The dynamic derivatives were successfully evaluated based on the linearization method. Neither thrust, nor blowing showed significant impact on the longitudinal dynamic derivatives.

Previously, the prediction of jet mixing noise from hot and cold isolated nozzle configurations has been studied with the means of RPM (Random Particle M esh) method using the Tam & Auriault or rather Tam, Pastouchenko and Viswanathan source model. The acoustical sources are generated as a reproduction of experimentally observed two-point cross-correlation functions using as input the turbulence statistics from RANS data. The sound propagation and extrapolation are performed with the linearized Euler equations in the near-field and with the Ffowcs-Williams & Hawkings method in the far-field. Efficient CAA computations are achieved exploiting the advantage of Fourier series decomposition for isolated axisymmetric and quasi-axisymmetric nozzle geometries. For investigation of installation effects the azimuthal-modal approach is however not applicable due to highly three-dimensional flow interactions, e.g. if a jet engine is mounted below an airfoil. Therefore, in contrast to the isolated nozzle configurations, in this case the resolution of computational domain in all three spatial dimensions is needed. Next to the RPM method, which is solely capable to generate two-dimensional acoustical sources, the FRPM method is available that is able to generate both, 2-D and 3-D sources. First test computations with FRPM method were conducted for a single stream jet, whereas the azimuthal-modal results of RPM were used as reference solution. The installed jet configurations are subsequently studied building on the FRPM computations of the single stream jet.

The aim of the investigation is to gain more certainty about the approach to evaluate the longitudinal stability and controllability of a high-lift configuration of a transport aircraft with circulation control. Since the work was carried out with a CFD RANS approach, a comprehensive meshing study was performed in advance.

The scope of this paper is to illustrate the installation effects of a turboprop engine on a high-lift configuration of a short take off and landing (STOL) aircraft with circulation control. In addition to the influence on the wing performance, the impact on the longitudinal static stability of the whole aircraft is also investigated. Furthermore, critical failure cases, namely one engine inoperative (OEI), as well as an asymmetric circulation control failure are assessed. Therefore, CFD calculations based on the Reynolds-averaged Navier-Stokes (RANS) equations were performed, whereas the propeller is modeled with an actuator disk.

Second graders (mean age, 8 years 3 months), fourth graders (mean age, 10 years 4 months), and adults verified telegraphic sentences with typical or atypical subject nouns and high or low dominant property predicates. The hypothesis tested was that the similarity in the attribute structures of category members to their superordinate prototype should be related to degree of typicality. Adult reaction time and error data supported the prototype model of semantic category structure. Second and fourth graders showed comparable property knowledge to adults, but evidenced different organizational patterns than predicted by the adult model. The results suggest that with development children learn to simultaneously use many attribute dimensions and to abstract the family resemblance structure and relative importance of category properties.

This research was concerned with retrieval processes which underlie conceptual clustering. In a free recall task with categorized lists, fifth graders' and adults' retrieval was examined temporally by means of interword response times. List organization and retrieval cue factors were manipulated in order to assess the developmental relevance of an hypothesized three component retrieval model. The results indicated that both age groups used a qualitatively similar retrieval strategy, involving search for and decoding of higher-order memory units. Providing retrieval cues eliminated the category search component, but also increased the likelihood of exhaustive recall attempts under random presentation conditions. The results were discussed in terms of the inter-relationships between storage and retrieval strategies. Age-related differences in retrieval time were attributed to insufficient reorganization during input and failure to attempt to recall all of a category's members.