blade loads
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2021 ◽  
Vol 11 (24) ◽  
pp. 12097
Author(s):  
Nikos Spyropoulos ◽  
George Papadakis ◽  
John M. Prospathopoulos ◽  
Vasilis A. Riziotis

In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced.


2021 ◽  
pp. 1-20
Author(s):  
Kenshiro Takahashi ◽  
Jun Arai ◽  
Takayuki Mori

The unsteady propeller forces of an underwater vehicle were numerically simulated using computational fluid dynamics to investigate the effects of the axial location of the stern planes. A benchmark study was undertaken using a three-bladed propeller; experimental results of the nominal inflow wake profile were analyzed and the unsteady propeller forces were measured. The numerical method was applied to predict the unsteady propeller forces in the SUBOFF model’s wake by varying the axial locations of the stern planes. Several remarks were made on the primary harmonics of the hull’s wakes and blade-rate propeller forces. Introduction The hydroacoustic noise, which matches multiples of the number of propeller blades and its rotational speed, known as “blade-rate (BR) noise,” has been increasingly used to manage hydroacoustics for naval vessels. BR noise can be caused by alternating blade loads owing to fluctuations in the angle of attack of the blades because marine propellers are operated in the nonuniform wake of ships’ hulls. The unsteady blade load produces unsteady propeller forces that are transmitted via the propeller shaft and bearing, thus producing undesirable vibration and noise. Although the resultant BR noise is a common issue for marine vessels, in particular, submarines and other underwater vehicles deployed for undersea defense systems and oceanographic survey systems require strict specifications for the acoustic signature. Therefore, the unsteady propeller forces must be improved for reduced detectability, because the vehicles should be able to operate without being discovered while sonar detection technology continues to improve.


2021 ◽  
Vol 9 (5) ◽  
pp. 482
Author(s):  
Danilo Calcagni ◽  
Giulio Dubbioso ◽  
Alessandro Capone ◽  
Fabrizio Ortolani ◽  
Riccardo Broglia

During maneuvers, propellers’ operation differs from their design due to strong modification of the wake field with respect to the straight-ahead motion. The consequent modification of the loads overstresses the mechanical components of the shaftline, exacerbates propeller side effects and worsens overall efficiency. Therefore, the analysis of these situations in the early design phase is pivotal to increase the operation capabilities and safety at sea. This task relies on novel tools capable to accurately predict the complex flow field that develops past the hull and the propeller loads. Since the solution of the fully coupled problem with the rotating propeller by viscous flow solver is impractical for routine applications, hybrid approaches are a viable alternative. In this paper, an interactive RANSE/BEM methodology is presented, where the propeller is replaced by rotating body forces that map the actual loading state of the blades, allowing a fully unsteady analysis of hull–propeller interaction. The methodology is applied to the straight ahead and 8.4° pure drift motions of a twin screw propulsive configuration. Last, but not least, the study presents a validation study with accurate experimental data of the nominal wake field and single blade loads.


Author(s):  
Felix Weiss ◽  
Christoph Kessler

AbstractIn contrast to analyses with constrained hub speed, the present study includes the dynamic response of coupled rotor-drivetrain modes in the aeromechanic simulation of rotor blade loads. The structural model of the flexible Bo105 rotor-drivetrain system is coupled to aerodynamics modeled by an analytical formulation of unsteady blade element loads combined with a generalized dynamic wake or a free wake, respectively. For two flight states, i. e. cruise flight and large blade loading, a time-marching autopilot trim of the rotor-drivetrain system in wind tunnel configuration is performed. The simulation results are compared to those of a baseline case with constant rotor hub speed. The comparison reveals a major change in the blade passage frequency harmonics of the lead-lag loads. Beside the full drivetrain model, reduced models are shown to accurately represent the drivetrain influence on blade loads, if the eigenfrequency of the coupled second collective lead-lag/drivetrain mode is properly predicted. In a sensitivity analysis, this eigenfrequency is varied by stiffness modification of a reduced drivetrain model. The resulting changes in blade loads are correlated to this eigenfrequency, which serves as a simple though accurate classification of the drivetrain regarding its influence on vibratory blade loads. Finally, the potential to improve lead-lag load predictions by application of a drivetrain model is demonstrated through the comparison of simulated loads with measurements from a wind tunnel test.


2021 ◽  
Author(s):  
Yichao Liu ◽  
Riccardo Ferrari ◽  
Jan-Willem van Wingerden

Abstract. Individual Pitch Control (IPC) is a well-known approach to reduce blade loads on wind turbines. Although very effective, IPC usually requires high levels of actuator activities, which significantly increases the pitch Actuator Duty Cycle (ADC). This will subsequently result in an increase of the wear on the bearings of the blades and make the current IPC design not economical viable. An alternative approach to this issue is to reduce the actuator activities by incorporating the output constraints in IPC. In this paper, a fully data driven IPC approach, which is called constrained Subspace Predictive Repetitive Control (cSPRC) is introduced. The output constraints can be explicitly considered in the control problem formulation via a Model Predictive Control (MPC) approach. The cSPRC approach will actively produce the IPC action for the necessary load reduction when the blade loads violate the output constraints. In this way, actuator activities can be significantly reduced. Two kinds of scenarios are simulated to illustrate the unique applications of the proposed method: wake-rotor overlap and turbulent wind conditions. Simulation results show that the developed cSPRC is able to account for the output constraints into the control problem formulation. Since the IPC action from cSPRC is only triggered to prevent violating the output constraints, the actuator activities are significantly reduced. This will help to reduce the pitch ADC, thus leading to an economical viable load control strategy. In addition, this approach allows the wind farm operator to design conservative bounds to guarantee the safety of the wind turbine control system.


Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3196 ◽  
Author(s):  
Krzysztof Rogowski ◽  
Martin Otto Laver Hansen ◽  
Galih Bangga

The purpose of this paper is to estimate the H-Darrieus wind turbine aerodynamic performance, aerodynamic blade loads, and velocity profiles downstream behind the rotor. The wind turbine model is based on the rotor designed by McDonnell Aircraft Company. The model proposed here consists of three fixed straight blades; in the future, this model is planned to be developed with controlled blades. The study was conducted using the unsteady Reynolds averaged Navier–Stokes (URANS) approach with the k-ω shear stress transport (SST) turbulence model. The numerical two-dimensional model was verified using two other independent aerodynamic approaches: a vortex model and the extended version of the computational fluid dynamics (CFD) code FLOWer. All utilized numerical codes gave similar result of the instantaneous aerodynamic blade loads. In addition, steady-state calculations for the applied airfoils were also made using the same numerical model as for the vertical axis wind turbine (VAWT) to obtain lift and drag coefficients. The obtained values of lift and drag force coefficients, for a Reynolds number of 2.9 million, agree with the predictions of the experiment and XFOIL over a wide range of angle of attack. A maximum rotor power coefficient of 0.5 is obtained, which makes this impeller attractive from the point of view of further research. Research has shown that, if this rotor were to work with fixed blades, it is recommended to use the NACA 1418 airfoil instead of the original NACA 0018.


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