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The installation of large bypass ratio engines on classical under wing configurations may lead to shock/boundary layer interaction on the wing lower surface, limiting the flight envelope in a similar way to classical buffet occurring on the wing suction side at high incidences in transonic flight. In this study, buffet effects on the lower surface of the wing induced by the installation of a Ultra-High-Bypass-Ratio through flow nacelle are assessed by means of wind tunnel testing. Unsteady pressure sensitive paint measurements were used to assess the pressure field on the wing with high temporal and spatial resolution. Strong unsteady shock motion associated with shock induced separation was found on the wing lower surface for various combinations of Mach number, Reynolds number and angle of attack. The wing lower surface buffet effects are found to increase with reducing angle of attack and are present over a wide range of Reynolds numbers. Preliminary spectral analysis suggests an upper limit for the buffet frequency at a Strouhal number of about 0.4.

The design of a new through flow nacelle for the Airbus XRF1 wind tunnel model is presented. The nacelle is representative of a modern UHBR turbofan engine for long range transport aircraft and was especially designed to investigate the interaction of buffet phenomena on the wing lower side, pylon and nacelle within the research unit FOR 2895. During the design process the performance of the through flow nacelle was evaluated by performing RANS simulations with the DLR TAU code using Spalart-Allmaras as well as Reynolds- Stress turbulence models. For the initial nacelle design simulations of the isolated nacelle were performed. Having obtained an initial nacelle shape, it was integrated in the XRF1 CAD model. A pylon geometry was designed and a baseline nacelle position and orientation was defined. The numerical simulations proved the configuration with nacelle and pylon shows adequate performance under cruise conditions without exhibiting unusual adverse effects on the aircraft. As intended, significant shock induced separations were observed on the wing lower side inboard of the nacelle for high speed off-design conditions with negative angles of attack allowing the investigation of buffet phenomena. The numerical results were also used to identify suitable locations for the pressure instrumentation on nacelle and pylon for the wind tunnel test at ETW.

The presentation summarizes the DLR contribution to the 3rd AIAA Sonic Boom Prediction Workshop. A grid generation approach using CENTAUR is presented. Near-field simulation results for the jet-plume interaction case and the C608 low boom geometry were presented. Results for both, workshop-provided and CENTAUR-generated grids are compared. A good grid convergence is achieved for fine grids.

Configurational aspects concerning the aerodynamics of a high-lift system with circulation control are investigated based on numerical investigations of two transport aircraft concepts. The two investigated concepts mainly differ in their engine type and position, vertical wing position, and wing sweep. The comparison of the two concepts indicate that all three aspects have a notable influence on the lift generation in landing configuration. A high wing position as well as an engine mounted in front of the main wing are both more favorable than a low wing position and an engine located behind the main wing in landing configuration. The wing sweep affects the lift generation as well as the stall behavior. The wing stall of the configuration with high positive wing sweep occurs due to flow separation in the outboard region, whereas the main wing of the configuration with low positive wing sweep stalls due to flow separation in the inboard region. The concept with engines mounted above the main wing trailing edge was furthermore investigated for intake flow distortion. While the landing configuration is uncritical concerning this matter, the take-off configuration reveals increasingly distorted intake flow with rising angle of attack.

A transport aircraft concept featuring over-the-wing-mounted nacelles (OWN)positioned aft of the wing’s trailing edge is investigated with numerical methods. The objective of the study is to compare two different approaches for integrating the nacelle to the airframe from an aerodynamic point of view. On one hand, a pylon mounted OWN configuration is chosen for installing the propulsion system. On the other hand,a closer coupling between wing and nacelle by embedding the OWN into the wing is examined. Both configurations will be analysed at a representative reference position and discussed in terms of similarities and differences. Afterwards, a positioning study with a free flying nacelle is conducted to explore the aerodynamic sensitivities of wing and nacelle for this engine airframe integration position. The results show that a favourable position with the potential for drag reduction can be found., {"references":["[1] Arntz, A., Atinault, O., Merl en, A., \"Exergy - Based Formulation for Aircraft Aeropropulsive Performance Assessment: Theoretical Development\", AIA A Journal, Vol. 53, No. 6 , pp. 1627 - 1639 , 2015","[ 2 ] Allmaras, S. R., Johnson, F. T., and Spalart, P. R., \"Modifications and Clarifications for the Implementation of the Spalart - Allmaras Turbulence Model,\" ICCFD7 - 1902, 7th International Conference on Computational Fluid Dynamics, Big Island, Hawaii, 9 - 13 July 2012","[3 ] CentaurSoft, 2017, www.centaursoft.com","[4 ] Delfs, J, Appel, C, Bernicke, P, Bl ech, C, Blinstrub, J, Heykena, C, Kumar, P, Kutscher, K, Lippitz, N, Rossian, L, Savoni, L, Lummer, M \"Aircraft and technology for low noise short take - off and landing\", 2017, 35th AIAA Applied Aerodynamics Conference Denver, Colorado","[5 ] DLR \"TAU - Code User Guide\", Release 2014.1.0, 2014, DLR","[6] Drela. M. \" Pow er Balance in Aerodynamic Flows\" , AIA A Journal, Vol. 47, No. 7 , pp. 1761 - 1771 , 2009","[7 ] European Commission \"Flightpath2050 – Europe's Vision for Aviation, Report on the High Level Group on Aviation Research\", ISBN 978 - 92 - 79 - 19724 - 6, 2011, www.acare4europe.org","[8 ] Heinze, W and Weiss, T, \"Main Data Sheet. A/C Type: SFB 880 Reference Aircraft REF3\", 2015, Project Data Sheet","[9 ] Heykena, C and Friedrichs, J., \" A erodynamic Investigation of an embedded U HBR - Engine Concept \" Proceedings of GPPS Forum 18, Global Power and Propulsion Society, Zurich, 10th - 12th January 2018","[10 ] Hooker, JW, Wick, A., Zeune, C, and Agelastos, A, \"Over Wing Nacelle Installations for Improved Energy Efficiency\" 31st AIAA Applied Aerodynamics Conference, San Diego, CA, 2013","[11 ] Kurzke , J., GasTurb 12 - Design and Off - Des ign Performance of Gas Turbines, 2012","[12 ] Menter, FR, \"Two - equation eddy - viscosity turbulence models for engineering applications\", AIAA Journal, 1994, Vol. 32, No. 8","[13 ] Radespiel, R, Berts ch, L, Heinze, W, \"High - Lift Re search for Future Transport Aircraft\", 2017 DLRK Munich","[14 ] Savoni, L. and Rudnik, R., \" Aerodynamic Assessment of Pylon - Mounted Over - the - Wing Engine Installations on a STOL Commercial Aircraft Concept \", In book: New Results in Numerical and Experimental Fluid Mechanics XI, Contributions to the 20th STAB/DGLR Symposium Braunschweig, Germany, 2016 pp.51 - 60, 2016","[15 ] Savoni, L. and Rudnik, R., \"Pylon Design for a Short Range Transport Aircraft wit h Over - the - Wing Mounted UHBR Engines\", 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018 - 0011) , 2018","[16] Wild, J., \"AeroForce Aerodynamic Force Analyzer\" Version 0.4, User manual, 1999"]}

The scope of the paper is to assess the potential of using circulation control at the vertical tail plane in order to increase the maximum rudder side force. Therefore, a numerical study on the rudder design is carried out, consisting of a 2D sensitivity study, an estimation of the 3D forces and moments via lifting line method, and a verification by 3D Reynolds-averaged Navier-Stokes (RANS) simulations. Compared to the baseline rudder, the lifting line method yields a 138% increase of the rudder yawing moment due to the use of circulation control. 3D RANS simulations verify the lifting line results. The deviation between yawing moments from the RANS computations and the lifting line method is less than 11%.

The aim of sub-project C1 of the Collaborative Research Center/Sonderforschungsbereich 880 (SFB 880) is to investigate numerically the flight mechanical characteristics of an aircraft with circulation controlled high-lift devices from an aerodynamic point of view. This paper summarizes the most important aspects of the work done so far. It begins with a basic analysis of the impact of varying blowing coefficients on the aircraft performance based on the wing-body configuration. Furthermore, an overview of the influence of the circulation controlled wing on the aerodynamics of the horizontal tail plane is presented. Eventually, the resulting longitudinal static stability and controllability behavior of the SFB 880’s reference aircraft is discussed. Additionally, the interaction of a circulation controlled wing and the slipstream of a wing mounted turboprop engine is investigated. Besides the studies of the static behavior, first results of the dynamic behavior, specifically the temporal behavior of circulation control after being activated are presented.

DLR’s contribution to the first AIAA High Lift Prediction Workshop (HiLiftPW-1) covers computations of all three scheduled test cases for the NASA trapezoidal wing in high lift configuration. The DLR finite volume code TAU has been employed as the flow solver. In a standard set-up the one-equation turbulence model of Spalart and Allmaras in the original formulation is used to model effects of turbulence. For selected grids and flow conditions, the k-ω SST model of Menter and a differential Reynolds stress model (SSG/LLR-ω ) developed by DLR have been considered. DLR contributed with two hybrid unstructured grid families to the workshop. The grids have been generated with the grid generation packages Centaur and Solar. A grid family with three Solar grids has been generated and provided to the workshop featuring grids of 12·10^6 , 37·10^6 , and 111·10^6 points for test case 1. In addition, a Solar grid of 37·10^6 points has been provided for test case 2, and a grid of 40·10^6 for the configuration including the slat and flap brackets (test case 3). DLR didn’t succeed in generating a fine-grid with the Centaur package. In order to complete a Centaur grid family with three grid levels an extra-coarse grid has been provided. Thus, the three levels of the Centaur grid family are realized by grids of 13·10^6 , 16·10^6 , and 32·10^6 points. In general a go o d agreement between the experimental evidence and the polar computations on the Solar and Centaur grids is found in terms of forces, moments and wing pressure distributions. The wing tip area with the rearward part of the main wing and the flap represents the most challenging part of the configuration, especially at angles of attack around maximum lift. The deviations between the TAU solutions and the experimental data in this area are only weakly influenced by the different grid topologies or turbulence models used. The influence of the grid resolution of both grid families is comparable, taking into account the different absolute resolution levels of both grid families. Including the slat and flap brackets leads to the expected lift decrease. Concerning the convergence properties, a strong dependence on the numerical start-up procedure has been detected in many of the computations at higher angles of attack.