06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Gust alleviation by spanwise load control applied on a forward and backward swept wing(2023) Klug, Lorenz; Ullah, Junaid; Lutz, Thorsten; Streit, Thomas; Heinrich, Ralf; Radespiel, RolfThe present paper investigates the feasibility of gust load alleviation at transonic speeds on a backward swept and a forward swept transport aircraft configuration. Spanwise-distributed control surfaces at the leading and trailing edges are employed to control gust-induced wing bending as well as wing torsion moments. The deflection amplitude and temporal flap actuation are determined by a novel scheme that builds on the aerodynamic strip theory. The aerodynamic effectiveness of the actuators is taken from a data base, computed from either 2D infinite swept wing simulations, or from yawed computations that take the effects of boundary-layer cross flow and the local sweep angle of the control surface into account. The present numerical flow simulations reveal that careful application of control laws at the trailing edge alleviates wing bending moments caused by strong vertical gusts by 85-90%, for both aircraft configurations. The application of leading-edge flaps introduces significant nonlinear aerodynamic interactions, that make the control of torsional moments comparably challenging. Here, the present results indicate that about 60% of wing torsion loads due to strong gusts can be removed.Item Open Access Reynolds number and wind tunnel wall effects on the flow field around a generic UHBR engine high-lift configuration(2020) Ullah, Junaid; Prachař, Aleš; Šmíd, Miroslav; Seifert, Avraham; Soudakov, Vitaly; Lutz, Thorsten; Krämer, EwaldRANS simulations of a generic ultra-high bypass ratio engine high-lift configuration were conducted in three different environments. The purpose of this study is to assess small scale tests in an atmospheric closed test section wind tunnel regarding transferability to large scale tests in an open-jet wind tunnel. Special emphasis was placed on the flow field in the separation prone region downstream from the extended slat cut-out. Validation with wind tunnel test data shows an adequate agreement with CFD results. The cross-comparison of the three sets of simulations allowed to identify the effects of the Reynolds number and the wind tunnel walls on the flow field separately. The simulations reveal significant blockage effects and corner flow separation induced by the test section walls. By comparison, the Reynolds number effects are negligible. A decrease of the incidence angle for the small scale model allows to successfully reproduce the flow field of the large scale model despite severe wind tunnel wall effects.Item Open Access Aerodynamic and acoustic simulations of thick flatback airfoils employing high order DES methods(2022) Bangga, Galih; Seel, Ferdinand; Lutz, Thorsten; Kühn, TimoThe results of high fidelity aerodynamic and acoustic computations of thick flatback airfoils are reported in the present paper. The studies are conducted on a flatback airfoil having a relative thickness of 30% with the blunt trailing edge thickness of 10% relative to chord. Delayed Detached-Eddy Simulation (DDES) approaches in combination with high order (5th) flux discretization WENO (Weighted Essentially Non-Oscillatory) and Riemann solver are employed. Two variants of the DES length scale calculation methods are compared. The results are validated against experimental data with good accuracy. The studies provide guideline on the mesh and turbulence modeling selection for flatback airfoil simulations. The results indicate that the wake breakdown is strongly influenced by the spanwise resolution of the mesh, which directly contributes to the prediction accuracy especially for drag force and noise emission. The Reynolds normal stress and the Reynolds stress component have the largest contributions on the mixing process, while the contribution of the component is minimal. Proper orthogonal decomposition is further performed to gain deeper insights into the wake characteristics.Item Open Access Assessment of low‐frequency aeroacoustic emissions of a wind turbine under rapidly changing wind conditions based on an aero‐servo‐elastic CFD simulation(2023) Wenz, Florian; Maas, Oliver; Arnold, Matthias; Lutz, Thorsten; Krämer, EwaldA meteorologically challenging situation that represents a demanding control task (rotational speed, pitch and yaw) for a wind turbine is presented and its implementation in a simulation is described. A high-fidelity numerical process chain, consisting of the computational fluid dynamics (CFD) solver FLOWer, the multi-body system (MBS) software SIMPACK and the Ffowcs Williams-Hawkings code ACCO, is used. With it, the aerodynamic, servoelastic and aeroacoustic (<20 Hz) behaviour of a generic wind turbine during a meteorological event with strong and rapid changes in wind speed and direction is investigated. A precursor simulation with the meteorological model system PALM is deployed to generate realistic inflow data. The simulated strong controller response of the wind turbine and the resulting aeroelastic behaviour are analysed. Finally, the low-frequency sound emissions are evaluated and the influence of the different operating and flow parameters during the variable inflow is assessed. It is observed that the wind speed and, linked to it, the rotational speed as well as the turbulence intensity are the main influencing factors for the emitted low-frequency sound power of the wind turbine. Yawed inflow, on the other hand, has little effect unless it changes the operational mode to load reduction, resulting in a swap of the main emitter from the blades to the tower.Item Open Access Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine(2018) Weihing, Pascal; Wegmann, Tim; Lutz, Thorsten; Krämer, Ewald; Kühn, Timo; Altmikus, AndreeThe present study investigates flow dynamics in the hub region of a wind turbine focusing on the influence of nacelle geometry on the root aerodynamics by means of Reynolds averaged Navier–Stokes simulations with the code FLOWer. The turbine considered is a generic version of the Enercon E44 converter incorporating blades with flat-back-profiled root sections. First, a comparison is drawn between an isolated rotor assumption and a setup including the baseline nacelle geometry in order to elaborate the basic flow features of the blade root. It was found that the nacelle reduces the trailed circulation of the root vortices and improves aerodynamic efficiency for the inner portion of the rotor; on the other hand, it induces a complex vortex system at the juncture to the blade that causes flow separation. The origin of these effects is analyzed in detail. In a second step, the effects of basic geometric parameters describing the nacelle have been analyzed with the purpose of increasing the aerodynamic efficiency in the root region. Therefore, three modification categories have been addressed: the first alters the nacelle diameter, the second varies the blade position relative to the nacelle and the third comprises modifications in the vicinity of the blade-nacelle junction. The impact of the geometrical modifications on the local flow physics are discussed and assessed with respect to aerodynamic performance in the blade root region. It was found that increasing the nacelle diameter deteriorates the root aerodynamics, since the flow separation becomes more pronounced. Possible solutions identified to reduce the flow separation are a shift of the blade in the direction of the rotation or the installation of a fairing fillet in the junction between the blade and the nacelle.Item Open Access About the suitability of different numerical methods to reproduce model wind turbine measurements in a wind tunnel with a high blockage ratio(2018) Klein, Annette Claudia; Bartholomay, Sirko; Marten, David; Lutz, Thorsten; Pechlivanoglou, George; Nayeri, Christian Navid; Paschereit, Christian Oliver; Krämer, EwaldThe paper describes the experimental and numerical investigation of a model wind turbine with a diameter of 3.0 m in a narrow wind tunnel. The objectives of the study are the provision of validation data, the comparison and evaluation of methods of different fidelity and the assessment of the influence of the wind tunnel walls. It turned out, that the accordance between the experimental and numerical results is good, but the wind tunnel walls have to be taken into account for the present setup.Item Open Access Utilizing high fidelity data into engineering model calculations for accurate wind turbine performance and load assessments under design load cases(2022) Bangga, Galih; Parkinson, Steven; Lutz, ThorstenWind turbines often have lower performance and experience higher loading in real operation compared to the original design performance. The reasons stem from the influences of complex atmospheric turbulence, blade contamination, surface imperfection and airfoil-shape changes. Engineering models used for designing wind turbines are limited to information derived from blade sectional datasets, while details on the three-dimensional blade characteristics are not captured. In these studies, a dedicated strategy to improve the prediction accuracy of engineering model calculations will be presented. The main aim is to present an elaborated effort to obtain a better estimate of the turbine loads in realistic operating conditions. The present studies are carried out by carefully utilizing data from high fidelity Computational Fluid Dynamics (CFD) computations into Blade Element Momentum (BEM) and Vortexline methods. The results are in a good agreement with detailed field measurement data of a 2.3 MW turbine. The studies are further extended to a large turbine having a rated power of 10 MW to provide an overview of its suitability for large turbines. Finally, calculations of the wind turbine under a realistic IEC design load case are demonstrated. The studies highlight important considerations for engineering modeling using BEM and Vortexline methods.Item Open Access An improved second-order dynamic stall model for wind turbine airfoils(2020) Bangga, Galih; Lutz, Thorsten; Arnold, MatthiasRobust and accurate dynamic stall modeling remains one of the most difficult tasks in wind turbine load calculations despite its long research effort in the past. In the present paper, a new second-order dynamic stall model is developed with the main aim to model the higher harmonics of the vortex shedding while retaining its robustness for various flow conditions and airfoils. Comprehensive investigations and tests are performed at various flow conditions. The occurring physical characteristics for each case are discussed and evaluated in the present studies. The improved model is also tested on four different airfoils with different relative thicknesses.The validation against measurement data demonstrates that the improved model is able to reproduce the dynamic polar accurately without airfoil-specific parameter calibration for each investigated flow condition and airfoil.This can deliver further benefits to industrial applications where experimental/reference data for calibrating the model are not always available.Item Open Access Aerodynamic interactions between distributed propellers and the wing of an electric commuter aircraft at cruise conditions(2024) Schollenberger, Michael; Kirsch, Bastian; Lutz, Thorsten; Krämer, Ewald; Friedrichs, JensBeneficial interactions that occur between propellers and the wing can be used to increase the overall efficiency of an aircraft in cruise flight. Different concepts with such interacting propellers are distributed propulsion (DP) and wingtip mounted propellers (WTP). For DP, a full distribution over the entire span can be distinguished from a partial distribution, concentrating the propellers at the wing tip area. The paper focuses on the energy efficiency in cruise flight as a result of the interactions and provides a general comparison of the concepts (WTP, full and partial DP) with a Beechcraft 1900D commuter aircraft as a reference. Parametric CFD studies varying the number and the position of the propellers are performed with a half-wing model. The simulations are performed with the second-order finite-volume flow solver TAU, developed by the German Aerospace Center (DLR), employing Reynolds-averaged Navier-Stokes (RANS) equations. The propellers are modeled using an Actuator Disk (ACD). An algorithm is used to reach cruise condition by iteratively adjusting the propeller rotational speed and the wing angle of attack. The CFD results are analyzed and evaluated with respect to the overall efficiency including the aerodynamic efficiency of the wing as well as the propulsive efficiency of the propellers. The parameter study shows that in cruise flight partial DP is more efficient than a full DP. The pure WTP configuration was found as the optimum of the propeller distribution along the wing, resulting in a saving of required power of 5.6%, relative to the reference configuration.