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The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation, about 42% increase in the power coefficient at λ = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.

The present works aim to investigate the effectiveness of active separation control by means of combined suction and vortex generator jets on the suction side of a very thick airfoil (40%) under tripped conditions. Fully resolved two-dimensional URANS and three-dimensional DDES simulations were carried out to assess the consistency of the results. It is observed for the baseline case that 2D URANS simulations are too optimistic while 3D DDES delivers an excellent agreement with the available experiment in the post stall region at α = 20°. The studies reveal that the proposed system is able to delay separation significantly, increasing the overall aerodynamic performance of the airfoil.

In the present paper the actuator line method is compared with fully resolved wind turbine simulations in offshore and complex terrain applications. In such flow fields, which are characterized by non-homogeneous and unsteady velocity distributions in the rotor plane, unsteady aerodynamic effects are likely and it is unclear how these characterize the wake development and load behavior of the wind turbine. The wake properties and loads are therefore compared for the case of a 5 MW wind turbine operating in a typical maritime atmosphere and a 2.4 MW onshore turbine located at a complex terrain site downstream of an escarpment. It was found that the actuator line predicts the wake structure, wake deflection and wake deficit in good agreement with the fully resolved simulation. However, an overestimation of velocity fluctuations was observed.

In the present study the actuator line method is used to simulate the wake of a wind turbine and ways to characterize its impact on the flight of a helicopter model through the wake are evaluated. The helicopter within the simulation setup is represented by a dynamic actuator line which was implemented into the flow solver FLOWer. In order to evaluate the loads on the helicopter the thrust force distribution is compared in different areas of the wake. For further improvement of the actuator line implementation different methods to evaluate the angle of attack are compared. This was examined as the angle of attack is a highly important parameter for the actuator line and helps to optimise the accuracy and performance of the actuator line method. As there is no experimental data available and the model of the helicopter comes with distinct simplifications the loads are compared to values without the wake of the wind turbine, thus in free flight.

In the present study, the performance of a small vertical axis wind turbine (VAWT) is investigated in realistic urban terrain, in presence of large buildings, hill and forested area. Normally, accelerated wind can be observed on the roof-top of the high-rise buildings. Thereby, different factors such as the orography, vegetation and presence of the buildings at the site etc. influence the inflow conditions strongly and subsequently the performance and loads of wind turbines. Due to the continuously varying inflow direction, inclination and highly turbulent nature of the wind, a detailed analysis of the flow field around the building is required. A two-stages approach is preferred to reduce complexity of the problem. In the first part, the inflow conditions are investigated in the large domain by means of CFD and in the second part, performance and loads of the roof-top mounted small VAWT are investigated.

This article presents various detached eddy simulation (DES) results of a commercial wind turbine under multiple inflow conditions in complex and flat terrain. Challenges regarding the meshing process of wind turbines in complex terrain are described and an approach to overcome those is presented. The main focus of the evaluation is blade load and power response to inflow turbulence and terrain effects, e.g. the change of the inclination angle or the speed-up due to a hill. To separate the different influences, the complexity of the simulation setup is increased stepwise. Starting with a baseline simulation in flat terrain and uniform inflow over adding atmospheric turbulence to a complex terrain simulation of a fully meshed rotating 3D wind turbine under atmospheric inflow.

This article presents detached eddy simulation (DES) results of a 5MW wind turbine in an unsteady atmospheric boundary layer. The evaluation performed in this article focuses on turbine blade loads as well as on the influence of atmospheric turbulence and tower on blade loads. Therefore, the turbulence transport of the atmospheric boundary layer to the turbine position is analyzed. To determine the influence of atmospheric turbulence on wind turbines the blade load spectrum is evaluated and compared to wind turbine simulation results with uniform inflow. Moreover, the influences of different frequency regimes and the tower on the blade loads are discussed. Finally, the normal force coefficient spectrum is analyzed at three different radial positions and the influence of tower and atmospheric turbulence is shown.

Minimizing the flow-induced noise is an important issue in the design of modern onshore wind turbines. There is a number of proven passive means to reduce the aeroacoustic noise, such as the implementation of serrations, porous trailing edges or the aeroacoustic airfoil design. The noise emission can be further reduced by active flow control techniques. In the present study the impact of distributed boundary layer suction on the noise emission of an airfoil and a complete rotor is investigated. Aerodynamic and aeroacoustic wind tunnel tests were performed for the NACA 64-418 airfoil and supplemented by numerical calculations. The aeroacoustic analyses have been conducted by means of the institute's Rnoise prediction scheme. The 2D studies have shown that noise reductions of 5 dB can be achieved by suction at moderate mass flow rates. To study the impact of three-dimensional effects numerical investigations have been conducted on the example of the generic NREL 5MW rotor with suction applied in the outer part of the blade. The predictions for the complete rotor provided smaller benefits compared to those for the isolated airfoil, mainly because the examined suction configurations were not optimized with respect to the extent of the suction patch and suction distribution.

A 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.

The present study evaluates the 3D flow occurring in the inboard area of an isolated rotor blade operating in stalled conditions. The delayed detached-eddy simulation approach is applied, and a high-order weighted essentially non-oscillatory scheme is used for flux computation. The load data obtained from available literature are used to validate the numerical computations, and a good agreement is obtained. Three different velocity components, namely, axial, tangential, and radial, are evaluated. An accelerated nozzle flow effect is observed in the root area, generating a distinct root flow vortex that travels downstream in a helical manner. Furthermore, a strong radial flow is observed within the separated flow area that causes 3D effects; this radial flow is strong only in the blade inboard area with a chord to radius ratio ( c/r ) that is larger than 0.1. Consequently, the 3D lift coefficient in the blade inboard area is remarkably larger compared with the corresponding 2D condition.