High-Fidelity Optimization Framework for Helicopter Rotors

An optimization framework for helicopter rotors based on high-fidelity coupled CFD/CSM analyses is presented. For this purpose the optimization software DAKOTA has been linked to a parametric geometry unit, a mesh generation unit and a fluid-structure module which consists of the DLR flow solver FLOWer coupled with the Comprehensive Rotorcraft Code HOST from Eurocopter. The optimization framework is first applied to various optimization problems in hover starting with the easy task of optimizing the twist rate for the 7A model rotor. The complexity of the optimizations is increased step by step and finishes with an optimization case involving all seven design parameters showing its superiority over simpler optimization problems with respect to the achieved improvement. In the next step the framework is operated in forward flight condition also for the optimization of the twist rate. Small improvements with respect to the 7A rotor are made though indicating the conflicting nature of hover and forward flight requirements. Thus a multi-objective optimization for the twist of the 7A rotor is carried out

Investigation of Aeroelastic Effects for a Helicopter Main Rotor in Hover

In the search of new rotorblades with increased performance and reduced noise emissions blade shapes become more and more complex. Due to this phenomenon and the slender form of the blades themselves Fluid-Structure- Interaction (FSI) becomes increasingly important. Therefore an optimization framework with a loose coupling approach in the loop between the block-stuctured 3D Navier- Stokes solver FLOWer and the Comprehensive Rotor Code HOST has been developed. In order to assess the influence of the FSI optimizations are first conducted on a pure aerodynamic basis. In a second step the optimizations are repeated with the same parameter combinations using the full loose coupling procedure. The results are then compared in order to isolate the effects of FSI. Various parameter combinations are analyzed since FSI heavily depends on the planform and therefore on the chosen parameters

High-Fidelity Optimization Framework for Helicopter Rotors

An optimization framework for helicopter rotors based on high-fidelity coupled CFD/CSM analyses is presented. For this purpose the optimization software DAKOTA has been linked to a parametric geometry unit, a mesh generation unit and a fluid-structure module which consists of the DLR flow solver FLOWer coupled with the Comprehensive Rotorcraft Code HOST from Eurocopter. The optimization framework is first applied to various optimization problems in hover starting with the easy task of optimizing the twist rate for the 7A model rotor. The complexity of the optimizations is increased step by step and finishes with an optimization case involving all seven design parameters showing its superiority over simpler optimization problems with respect to the achieved improvement. In the next step the framework is operated in forward flight condition also for the optimization of the twist rate. Small improvements with respect to the 7A rotor are made though indicating the conflicting nature of hover and forward flight requirements. Thus a multi-objective optimization for the twist of the 7A rotor is carried out

High-fidelity optimization framework for helicopter rotors

An optimization framework for helicopter rotors based on high-fidelity coupled CFD/CSM analyses is presented. For this purpose the optimization software DAKOTA has been linked to a parametric geometry unit, a mesh generation unit and a fluid�structure module which consists of the DLR flow solver FLOWer coupled with the Comprehensive Rotorcraft Code HOST from Eurocopter. The optimizations themselves are carried out on coarse meshes while the results are verified on fine meshes. The mesh discretization in hover is based on a preliminary mesh refinement study. For forward flight the mesh discretization is in alignment with values from the literature. The optimization framework is first applied to various optimization problems in hover starting with the easy task of optimizing the twist rate for the 7A model rotor. The second optimization case investigates the effects of a combined Twist and Sweep optimization. The last optimization in hover involves all design parameters, namely Twist, Chord, Sweep, Anhedral, Transtart, Tipstart showing its superiority over simpler optimization problems with respect to the achieved improvement. In the next step the framework is operated in forward flight. The optimization of Twist yields only small improvements in comparison with the 7A rotor indicating that the baseline rotor is already optimized for this type of flow condition. Finally a multi-objective optimization for Twist is carried out in order to find a compromise design between the conflicting goal functions for hover and forward flight

Mehrpunktoptimierung eines Hubschrauberrotors unter Berücksichtigung der Fluid-Struktur-Wechselwirkung

Das in dieser Arbeit vorgestellte Verfahren ist in der Lage, den Rotorblattgrundriss sowohl im Schwebe- als auch im Vorwärtsflug anhand eines mathematischen Optimierungsalgorithmus sowie unter Verwendung hochwertiger Strömungssimulationen und unter Berücksichtigung der Fluid-Struktur-Wechselwirkung automatisch zu optimieren. Hierzu wird eine Parametrisierung der Geometrie vorgenommen, die mit einem Minimum an Entwurfsparametern auskommt und dennoch eine große Bandbreite von möglichen Grundrissformen erlaubt. Aufgrund der langen Rechenzeiten der CFD-Verfahren werden die Optimierungen auf groben Rechennetzen durchgeführt. Im Vorwärtsflug erfolgt die Strömungssimulation darüber hinaus auf Basis von Einzelblattrechnungen. Im Anschluss an die Optimierung wird das Ergebnis anhand von Berechnungen auf feinen Netzen und im Vorwärtsflug durch eine Mehrblattrechnung unter Verwendung der Chimera-Technik verifiziert. Im Schwebeflug werden die Unterschiede zwischen einer Optimierung mit starrer und elastischer Blattmodellierung analysiert. Während die Fluid-Struktur- Wechselwirkung einen vernachlässigbaren Einfluss auf die Optimierung der Verwindung ausübt, muss sie bei der Optimierung anderer Parameter wie z.B. der Pfeilung unbedingt berücksichtig werden. Durch die Optimierung aller Parameter wird im Schwebeflug eine Verbesserung der Gütezahl von fast 11\% erreicht. Im Vorwärtsflug werden aufgrund der langen Rechenzeiten nur Optimierungen mit einzelnen Parametern durchgeführt. Hierbei zeigt sich, dass sich die Verwindung und die V-Stellung des Ausgangsrotors bereits sehr nah an den optimalen Werten befinden. Durch die Optimierung der Pfeilung bzw. der Profiltiefe lässt sich noch eine geringe Verbesserung erzielen. Die Einzel- und Mehrblattrechnungen zeigen in allen Fällen eine hervorragende Übereinstimmung. Die letzte Untersuchung widmet sich der Mehrpunktoptimierung der Verwindung mithilfe eines Wichtungsansatzes. Dadurch gelingt es, die Pareto-Front für den Schwebe- und Vorwärtsflug darzustellen, um so einen geeigneten Kompromiss zwischen den beiden Flugzuständen zu finden

CFD Simulations of the New MEXICO Rotor Experiment under Yawed Flow

This paper describes the conduction of CFD simulations with DLR’s flow solver TAU for comparison with the experimental data that has been used within the third phase of the MexNext-III project. More precisely computations for three different inflow velocities under yawed flow condition have been conducted and compared to the experimental results. Important aspects of the simulations such as a sufficiently long simulation time or a sufficiently small time-step are discussed. At first local flow quantities such as the flow velocity along axial and radial traverses, pressure distributions at four radial stations and normal and tangential forces at these sections are compared. Subsequently the integral rotor quantities i.e. rotor thrust and rotor torque are revised. The integration of the CFD results is performed using the complete surface dataset as well as two subsets.The comparison proves that the agreement can substantially be improved if the subset resembles the experimental dataset. Furthermore the integration of the experimental dataset is reviewed and a weak spot in the current reconstruction procedure of the trailing edge pressure is identified. The proposed alternative provides evidence that further improvements are possible.The final comparison shows an acceptable agreement for the medium and high inflow speed case yielding 0% and 10% difference for integral thrust and 9% and 14% for integral torque. The results for the low inflow speed case are divers: while the agreement for the integral thrust is excellent, it is less satisfactory for the integral torque which amounts to 41%

Sensitivity analysis of a wind rotor blade utilizing a multi-disciplinary tool chain

Due to the multi-disciplinary nature in the design of wind turbines, developers and manufacturers face several challenges. One of them is the exchange of model data between the different disciplines, e.g. aerodynamic or structural dynamics. To overcome the problems of data exchange between the disciplines the Common Parametric Aircraft Configuration Schema (CPACS) has been developed by the German Aerospace Center (DLR). Based on this data scheme a multi-disciplinary tool chain and the verification of their components are presented. Due to some similarities in the design of aircraft wings and wind turbine blades, the tool DELiS has been extended to create structural finite element models of wind turbine blades. The tool has been validated to an industrial rotor and the DTU 10-MW reference rotor blade. The finite element models are dynamically reduced and exported as flexible bodies to the multi-body simulation tool Simpack. For aeroelastic analyses an aerodynamic model is coupled to the multi-body simulation tool. The aerodynamic models can be either a high-fidelity CFD-simulation or a low-fidelity model based blade element momentum theory. This paper illustrates guidelines for the development of a multi-disciplinary tool chain and its interfaces. Based on this framework, sensitivities of parameter changes as well as parameter optimization can be done utilizing a trained neuronal network. The methodology of this analysis with a low number of parameters will allow a sensitivity analysis for complete rotor blade designs in the future

Towards Multidisciplinary Wind Turbine Design using High-Fidelity Methods

Reliable predictions for wind turbines become more and more difficult with the increase in overall size and weight. On the one hand external factors such as the influence of wind shear become more important for bigger turbines, internal factors such as structural layout and challenges in the manufacturing process need to be addressed on the other hand. Accurate aerodynamic simulations are an essential requirement for further analyses of aeroelastic stability and aeroacoustic footprint. While the calculations in all of these individual disciplines are challenging the combined simulation of all these disciplines, namely the multidisciplinary simulation is a tough but gainful undertaking. This task is being addressed in the DLR project MERWind which will be presented here. The focus of the paper lays on the aerodynamic and aeroelastic simulation of the NREL 5MW wind turbine using high-fidelity methods