TY - CHAP A1 - Götten, Falk A1 - Finger, Felix A1 - Havermann, Marc A1 - Braun, Carsten A1 - Marino, Matthew A1 - Bil, Cees T1 - Full Configuration Drag Estimation of Small-to-Medium Range UAVs and its Impact on Initial Sizing Optimization T2 - Deutscher Luft- und Raumfahrtkongress - DLRK 2020 Y1 - 2020 ER - TY - CHAP A1 - Götten, Falk A1 - Finger, Felix A1 - Marino, Matthew A1 - Bil, Cees A1 - Havermann, Marc A1 - Braun, Carsten T1 - A review of guidelines and best practices for subsonic aerodynamic simulations using RANS CFD T2 - Asia-Pacific International Symposium on Aerospace Technology (APISAT), At Gold Coast, Australia, 04. - 06. Dezember 2019 Y1 - 2019 SN - 978-1-925627-40-4 ER - TY - CHAP A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Gomez, Francisco A1 - Bil, Cees T1 - On the Applicability of Empirical Drag Estimation Methods for Unmanned Air Vehicle Design Read More: https://arc.aiaa.org/doi/10.2514/6.2018-3192 T2 - 2018 Aviation Technology, Integration, and Operations Conference, AIAA AVIATION Forum Y1 - 2018 U6 - http://dx.doi.org/10.2514/6.2018-3192 SN - 1533-385X N1 - AIAA 2018-3192 SP - Article 3192 ER - TY - JOUR A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Gomez, Francisco A1 - Bil, Cees T1 - RANS Simulation Validation of a Small Sensor Turret for UAVs JF - Journal of Aerospace Engineering N2 - Recent Unmanned Aerial Vehicle (UAV) design procedures rely on full aircraft steady-state Reynolds-Averaged-Navier-Stokes (RANS) analyses in early design stages. Small sensor turrets are included in such simulations, even though their aerodynamic properties show highly unsteady behavior. Very little is known about the effects of this approach on the simulation outcomes of small turrets. Therefore, the flow around a model turret at a Reynolds number of 47,400 is simulated with a steady-state RANS approach and compared to experimental data. Lift, drag, and surface pressure show good agreement with the experiment. The RANS model predicts the separation location too far downstream and shows a larger recirculation region aft of the body. Both characteristic arch and horseshoe vortex structures are visualized and qualitatively match the ones found by the experiment. The Reynolds number dependence of the drag coefficient follows the trend of a sphere within a distinct range. The outcomes indicate that a steady-state RANS model of a small sensor turret is able to give results that are useful for UAV engineering purposes but might not be suited for detailed insight into flow properties. Y1 - 2019 U6 - http://dx.doi.org/10.1061/(ASCE)AS.1943-5525.0001055 SN - 1943-5525 VL - 32 IS - 5 PB - ASCE CY - New York ER - TY - JOUR A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Marino, Matthew A1 - Bil, Cees T1 - Airfoil drag at low-to-medium reynolds numbers: A novel estimation method JF - AIAA Journal N2 - This paper presents a novel method for airfoil drag estimation at Reynolds numbers between 4×10⁵ and 4×10⁶. The novel method is based on a systematic study of 40 airfoils applying over 600 numerical simulations and considering natural transition. The influence of the airfoil thickness-to-chord ratio, camber, and freestream Reynolds number on both friction and pressure drag is analyzed in detail. Natural transition significantly affects drag characteristics and leads to distinct drag minima for different Reynolds numbers and thickness-to-chord ratios. The results of the systematic study are used to develop empirical correlations that can accurately predict an airfoil drag at low-lift conditions. The new approach estimates a transition location based on airfoil thickness-to-chord ratio, camber, and Reynolds number. It uses the transition location in a mixed laminar–turbulent skin-friction calculation, and corrects the skin-friction coefficient for separation effects. Pressure drag is estimated separately based on correlations of thickness-to-chord ratio, camber, and Reynolds number. The novel method shows excellent accuracy when compared with wind-tunnel measurements of multiple airfoils. It is easily integrable into existing aircraft design environments and is highly beneficial in the conceptual design stage. Y1 - 2020 U6 - http://dx.doi.org/10.2514/1.J058983 SN - 1533-385X VL - 58 IS - 7 SP - 2791 EP - 2805 PB - AIAA CY - Reston, Va. ER - TY - JOUR A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Marino, Matthew A1 - Bil, Cees T1 - Wind-tunnel and CFD investigations of UAV landing gears and turrets – Improvements in empirical drag estimation JF - Aerospace Science and Technology N2 - This paper analyzes the drag characteristics of several landing gear and turret configurations that are representative of unmanned aircraft tricycle landing gears and sensor turrets. A variety of these components were constructed via 3D-printing and analyzed in a wind-tunnel measurement campaign. Both turrets and landing gears were attached to a modular fuselage that supported both isolated components and multiple components at a time. Selected cases were numerically investigated with a Reynolds-averaged Navier-Stokes approach that showed good accuracy when compared to wind-tunnel data. The drag of main gear struts could be significantly reduced via streamlining their cross-sectional shape and keeping load carrying capabilities similar. The attachment of wheels introduced interference effects that increased strut drag moderately but significantly increased wheel drag compared to isolated cases. Very similar behavior was identified for front landing gears. The drag of an electro-optical and infrared sensor turret was found to be much higher than compared to available data of a clean hemisphere-cylinder combination. This turret drag was merely influenced by geometrical features like sensor surfaces and the rotational mechanism. The new data of this study is used to develop simple drag estimation recommendations for main and front landing gear struts and wheels as well as sensor turrets. These recommendations take geometrical considerations and interference effects into account. Y1 - 2020 U6 - http://dx.doi.org/10.1016/j.ast.2020.106306 SN - 1270-9638 VL - 107 IS - Art. 106306 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Marino, Matthew A1 - Bil, Cees T1 - Improved Form Factor for Drag Estimation of Fuselages with Various Cross Sections JF - Journal of Aircraft N2 - The paper presents an aerodynamic investigation of 70 different streamlined bodies with fineness ratios ranging from 2 to 10. The bodies are chosen to idealize both unmanned and small manned aircraft fuselages and feature cross-sectional shapes that vary from circular to quadratic. The study focuses on friction and pressure drag in dependency of the individual body’s fineness ratio and cross section. The drag forces are normalized with the respective body’s wetted area to comply with an empirical drag estimation procedure. Although the friction drag coefficient then stays rather constant for all bodies, their pressure drag coefficients decrease with an increase in fineness ratio. Referring the pressure drag coefficient to the bodies’ cross-sectional areas shows a distinct pressure drag minimum at a fineness ratio of about three. The pressure drag of bodies with a quadratic cross section is generally higher than for bodies of revolution. The results are used to derive an improved form factor that can be employed in a classic empirical drag estimation method. The improved formulation takes both the fineness ratio and cross-sectional shape into account. It shows superior accuracy in estimating streamlined body drag when compared with experimental data and other form factor formulations of the literature. Y1 - 2020 U6 - http://dx.doi.org/10.2514/1.C036032 SN - 1533-3868 SP - 1 EP - 13 PB - AIAA CY - Reston, Va. ER - TY - JOUR A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Marino, Matthew A1 - Bil, Cees T1 - Aerodynamic Investigations of UAV Sensor Turrets - A Combined Wind-tunnel and CFD Approach JF - SciTech 2021, AIAA SciTech Forum, online, WW, Jan 11-15, 2021 Y1 - 2021 U6 - http://dx.doi.org/10.2514/6.2021-1535 SP - 1 EP - 12 PB - AIAA CY - Reston, Va. ER - TY - CHAP A1 - Hailer, Benjamin A1 - Weber, Tobias A1 - Arent, Jan-Christoph T1 - Manufacturing Process Simulation for Autoclave-Produced Sandwich Structures T2 - Proceedings of SAMPE Europe Conference 2019, Nantes, France Y1 - 2019 SP - 1 EP - 8 ER - TY - JOUR A1 - Hailer, Benjamin A1 - Weber, Tobias A1 - Neveling, Sebastian A1 - Dera, Samuel A1 - Arent, Jan-Christoph A1 - Middendorf, Peter T1 - Development of a test device to determine the frictional behavior between honeycomb and prepreg layers under realistic manufacturing conditions JF - Journal of Sandwich Structures & Materials N2 - In the friction tests between honeycomb with film adhesive and prepreg, the relative displacement occurs between the film adhesive and the prepreg. The film adhesive does not shift relative to the honeycomb. This is consistent with the core crush behavior where the honeycomb moves together with the film adhesive, as can be seen in Figure 2(a). The pull-through forces of the friction measurements between honeycomb and prepreg at 1 mm deformation are plotted in Figure 17(a). While the friction at 100°C is similar to the friction at 120°C, it decreases significantly at 130°C and exhibits a minimum at 140°C. At 150°C, the friction rises again slightly and then sharply at 160°C. Since the viscosity of the M18/1 prepreg resin drops significantly before it cures [23], the minimum friction at 140°C could result from a minimum viscosity of the mixture of prepreg resin and film adhesive before the bond subsequently cures. Figure 17(b) shows the mean value curve of the friction measurements at 140°C. The error bars, which represent the standard deviation, reveal the good repeatability of the tests. The force curve is approximately horizontal between 1 mm and 2 mm. The friction then slightly rises. As with interlaminar friction measurements, this could be due to the fact that resin is removed by friction and the proportion of boundary lubrication increases. Figure 18 shows the surfaces after the friction measurement. The honeycomb cell walls are clearly visible in the film adhesive. There are areas where the film adhesive is completely removed and the carrier material of the film adhesive becomes visible. In addition, the viscosity of the resin changes as the curing progresses during the friction test. This can also affect the force-displacement curve. Y1 - 2020 U6 - http://dx.doi.org/10.1177/1099636220923986 SN - 1530-7972 IS - Volume 23, Issue 7 SP - 3017 EP - 3043 PB - Sage CY - London ER - TY - JOUR A1 - Haj Ayed, A. A1 - Kusterer, K. A1 - Funke, Harald A1 - Keinz, Jan A1 - Striegan, Constantin A1 - Bohn, D. T1 - Experimental and numerical investigations of the dry-low-NOx hydrogen micromix combustion chamber of an industrial gas turbine JF - Propulsion and power research Y1 - 2015 U6 - http://dx.doi.org/10.1016/j.jppr.2015.07.005 SN - 2212-540X VL - Vol. 4 IS - Iss. 3 SP - 123 EP - 131 ER - TY - JOUR A1 - Haj Ayed, A. A1 - Kusterer, K. A1 - Funke, Harald A1 - Keinz, Jan A1 - Striegan, Constantin A1 - Bohn, D. T1 - Improvement study for the dry-low-NOx hydrogen micromix combustion technology JF - Propulsion and power research Y1 - 2015 U6 - http://dx.doi.org/10.1016/j.jppr.2015.07.003 SN - 2212-540X VL - Vol. 4 IS - Iss. 3 SP - 132 EP - 140 ER - TY - CHAP A1 - Hallmann, Marcus A1 - Heidecker, Ansgar A1 - Schlotterer, Markus A1 - Dachwald, Bernd T1 - GTOC8: results and methods of team 15 DLR T2 - 26th AAS/AIAA Space Flight Mechanics Meeting, Napa, CA N2 - This paper describes the results and methods used during the 8th Global Trajectory Optimization Competition (GTOC) of the DLR team. Trajectory optimization is crucial for most of the space missions and usually can be formulated as a global optimization problem. A lot of research has been done to different type of mission problems. The most demanding ones are low thrust transfers with e.g. gravity assist sequences. In that case the optimal control problem is combined with an integer problem. In most of the GTOCs we apply a filtering of the problem based on domain knowledge. Y1 - 2016 N1 - 26th AAS/AIAA Space Flight Mechanics Meeting, February 14-18, 2016, Napa, California, U.S.A. Napa, CA ER - TY - JOUR A1 - Hammer, Thorben A1 - Quitter, Julius A1 - Mayntz, Joscha A1 - Bauschat, J.-Michael A1 - Dahmann, Peter A1 - Götten, Falk A1 - Hille, S. A1 - Stumpf, E. T1 - Free fall drag estimation of small-scale multirotor unmanned aircraft systems using computational fluid dynamics and wind tunnel experiments JF - CEAS Aeronautical Journal N2 - New European Union (EU) regulations for UAS operations require an operational risk analysis, which includes an estimation of the potential danger of the UAS crashing. A key parameter for the potential ground risk is the kinetic impact energy of the UAS. The kinetic energy depends on the impact velocity of the UAS and, therefore, on the aerodynamic drag and the weight during free fall. Hence, estimating the impact energy of a UAS requires an accurate drag estimation of the UAS in that state. The paper at hand presents the aerodynamic drag estimation of small-scale multirotor UAS. Multirotor UAS of various sizes and configurations were analysed with a fully unsteady Reynolds-averaged Navier–Stokes approach. These simulations included different velocities and various fuselage pitch angles of the UAS. The results were compared against force measurements performed in a subsonic wind tunnel and provided good consistency. Furthermore, the influence of the UAS`s fuselage pitch angle as well as the influence of fixed and free spinning propellers on the aerodynamic drag was analysed. Free spinning propellers may increase the drag by up to 110%, depending on the fuselage pitch angle. Increasing the fuselage pitch angle of the UAS lowers the drag by 40% up to 85%, depending on the UAS. The data presented in this paper allow for increased accuracy of ground risk assessments. KW - Multirotor UAS KW - Drag estimation KW - CFD KW - Wind tunnel experiments KW - Wind milling Y1 - 2023 U6 - http://dx.doi.org/10.1007/s13272-023-00702-w SN - 1869-5590 (Online) SN - 1869-5582 (Print) N1 - Corresponding author: Thorben Hammer PB - Springer CY - Wien ER - TY - BOOK A1 - Harder, Jörn T1 - Simulation lokaler Fließvorgänge in Polykristallen Y1 - 1997 SN - 3-920395-27-1 N1 - Serie Braunschweiger Schriften zur Mechanik , 28 ; Zugl.: Braunschweig, Techn. Univ., Diss., 1996 PB - Mechanik-Zentrum der Technischen Universität CY - Braunschweig ER - TY - BOOK A1 - Harder, Jörn T1 - Zur Messung von Werkstoffparametern im Torsionsschwingversuch Y1 - 1990 CY - Braunschweig ER - TY - JOUR A1 - Harder, Jörn T1 - A crystallographic model for the study of local deformation processes in polycrystals JF - International journal of plasticity. 15 (1999), H. 6 Y1 - 1999 SN - 0749-6419 N1 - Online: http://opus.tu-bs.de/opus/volltexte/1999/10/pdf/10_1.pdf SP - 605 EP - 624 ER - TY - CHAP A1 - Haugg, Albert Thomas A1 - Kreyer, Jörg A1 - Kemper, Hans A1 - Hatesuer, Katerina A1 - Esch, Thomas T1 - Heat exchanger for ORC. adaptability and optimisation potentials T2 - IIR International Rankine 2020 Conference N2 - The recovery of waste heat requires heat exchangers to extract it from a liquid or gaseous medium into another working medium, a refrigerant. In Organic Rankine Cycles (ORC) on Combustion Engines there are two major heat sources, the exhaust gas and the water/glycol fluid from the engine’s cooling circuit. A heat exchanger design must be adapted to the different requirements and conditions resulting from the heat sources, fluids, system configurations, geometric restrictions, and etcetera. The Stacked Shell Cooler (SSC) is a new and very specific design of a plate heat exchanger, created by AKG, which allows with a maximum degree of freedom the optimization of heat exchange rate and the reduction of the related pressure drop. This optimization in heat exchanger design for ORC systems is even more important, because it reduces the energy consumption of the system and therefore maximizes the increase in overall efficiency of the engine. Y1 - 2020 U6 - http://dx.doi.org/10.18462/iir.rankine.2020.1224 N1 - Conference: IIR International Rankine 2020 Conference - Heating, Cooling, Power Generation. Glasgow, 2020. ER - TY - BOOK A1 - Havermann, Marc T1 - Strahlmischung und Druckrückgewinn in Überschall-Innenströmungen Y1 - 2000 SN - 3-86073-761-9 N1 - Aachener Beiträge zum Maschinenbau ; 2 ; Zugl. Aachen, Techn. Hochsch., Diss., 1999 PB - Mainz CY - Aachen ER - TY - BOOK A1 - Havermann, Marc T1 - PIV measurements in shock tunnels : PivNet 2, Final Workshop, Göttingen, 07. - 08.09.2006 Y1 - 2006 N1 - Publication / Institut Franco-Allemand de Recherches de Saint Louis ; 644 PB - ISL CY - Saint-Louis ER -