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The current article describes the conceptual design of a rotor for a 5 MW machine situated at an offshore site in China (OffWindChina). The OffWindChina 5 MW rotor design work was divided into two parts between the Technical University of Denmark (DTU) and the Chong Qing University (CQU). The two parts consist of the aeroelastic and structural design phases. The aeroelastic part determines the optimal outer blade shape in terms of cost of energy (COE), while the structural part determines the internal laminate layup to achieve a minimum blade mass. Each part is performed sequentially using in-house optimization tools developed at DTU and CQU. The designed blade yields a high energy output while maintaining the structural feasibility with respect to international standards.

Noise generated from wind turbines is a big challenge for the wind energy industry to develop further onshore wind energy. The traditional way of reducing noise is to design low noise wind turbine airfoils and blades. A wind turbine operating under wind shear and in yaw produces periodic changes of blade loading, which intensifies the amplitude modulation (AM) of the generated noise, and thus can give more annoyance to the people living nearby. In this paper, the noise emission from a wind turbine under wind shear and yaw is modelled with an advanced fluid-structure-acoustics framework, and then controlled with a pitch control strategy. The numerical tool used in this study is the coupled Navier–Stokes/Actuator Line model EllipSys3D/AL, structure model FLEX5, and noise prediction model (Brooks, Pope and Marcolini: BPM) framework. All simulations and tests were made on the NM80 wind turbine equipped with three blades made by LM Wind Power. The coupled code was first validated against field load measurements under wind shear and yaw, and a fairly good agreement was obtained. The coupled code was then used to study the noise source control of the turbine under wind shear and yaw. Results show that in the case of a moderate wind shear with a shear exponent of 0.3, the pitch control strategy can reduce the mean noise emission about 0.4 dB and reduce slightly the modulation depth that mainly occurs in the low-frequency region.

This article describes Computational Fluid Dynamics (CFD) simulations of flows in a wind farm in complex terrain in Shaanxi, China and the comparisons of the computational results with utility scale field measurements. The CFD simulations performed in the study are using either a Reynolds-Averaged Navier–Stokes (RANS) or Large-Eddy Simulation (LES) solver. The RANS method together with an Actuator Disc (AD) approach is employed to predict the performance of the 25 wind turbines in the farm, while the LES and Actuator Line (AL) technique is used to obtain a detailed description of the flow field around a specific wind turbine #14 near two met masts. The AD-RANS simulation results are compared with the mean values of power obtained from field measurements. Furthermore, the AL-LES results are compared with the mean values of power, rotor speed, and wind speed measured from the wind turbine and its nearby two masts. Results from the simulations indicate that both AD-RANS and AL-LES methods can reasonably predict the performance of the wind farm and wind turbine #14, respectively, in complex terrain in Shaanxi. The mean percent difference obtained for power in the AD-RANS simulations was approximately 20%. Percent differences obtained for power and rotor RPM in the AL-LES varied between 0.08% and 11.6%. The mean percent differences in the AL-LES for power and rotor RPM are approximately 7% and 1%, respectively.

The development of reliable Fluid-Structure Interaction (FSI) simulation tools and models for the wind turbines is a critical step in the design procedure towards achieving optimized large wind turbine structures. Such approach will mitigate the aeroelastic instabilities like: torsional flutter, stall flutter and edgewise instability that introduce extra stresses to the turbine structure leading to reduced life time and substantial failures. In this study, FSI simulations were held using the commercial package Ansys v18.2 solvers as a preliminary step towards our on-going development of a reliable Open-Source solver. These simulations were applied to the full-scale rotor blades of the NREL 5MW reference horizontal axis wind turbine. The aerodynamic loads and structural responses computations were carried out using a steady-state FSI analysis. The computations were run on the Kyushu University multi-core Linux cluster using the public domain openMPI implementation of the standard message passing interface (MPI). Finally, the results were validated against the Technical University of Denmark's (DTU) MIRAS aeroelastic code results as well as the widely used FLEX5-Q3UIC and FAST codes in different cases showing reasonable agreement.

Anti-frost fans (AFFs) are widely used in agriculture to reduce the frost damage to crops. The small wind turbine rotor design code (SWRDC) was adapted to design the blades of an anti-frost fan to maximize the mass flow rate through the rotor while minimizing the blade mass and aerodynamic noise. Using a random sample set of 60 baseline designs, the design is iterated using a genetic algorithm to obtain an optimized design with a mass flow rate of 3.11 kg/s, a blade mass of 6.96 kg, and with a noise level of 72.8 dB.

The manuscript presents a novel aero‐hydro‐servo‐elastic coupling framework, MIRAS‐HAWC2. In this coupling, the wind turbine blades and rotor‐wake aerodynamics are modeled using a modified lifting‐line theory which accounts for blade curvature, combined with a hybrid vortex method. The wind turbine structure and foundation are modeled using a finite‐element and multi‐body system approach. Last, hydrodynamics are modeled using Airy wave theory together with Morison's equation. An initial assessment of the performance of the aeroelastic coupling framework has been performed for steady rotor‐only cases, assuming laminar inflow without shear. This included a comparison against fully resolved computational fluid dynamics, for both stiff and flexible blades showing an excellent agreement. In a second stage, the aero‐hydro‐servo‐elastic coupling is used, comparing MIRAS‐HAWC2 as well as blade‐element momentum‐based simulations with selected results from the Offshore Code Comparison Collaboration projects (OC3 and OC4), which study the NREL 5 MW turbine mounted on different offshore support structures. A good agreement has been obtained for the simulations of a monopile with rigid foundation, a tripod, and jacket support structures.

This paper describes numerical noise propagation calculations of a single wind turbine in complex terrain near a town in Central Denmark. The purpose of the work is to estimate the noise level at increasing distances from a single wind turbine and investigate the effect of complex terrain. Results indicate that time varying numerical noise propagation predictions of wind turbines in complex terrain can be achieved by using computational fluid dynamics via large-eddy simulation (LES) and the Technical University of Denmark's noise propagation tool based on the parabolic equation. The wind turbine is modeled using the actuator line approach. The results from this project will have significant social, environmental, and economic impact, since accurate predictions of wind turbine noise propagation can be used to develop noise mitigation strategies to increase the public acceptance of wind energy.

An in-house aero-elastic vortex code, called MIRAS, is used to investigate the aerodynamic performance of winglets and sweep on horizontal-axis wind turbine (HAWT) blades in simple and complex inflow conditions. Previous studies using vortex codes applied to study winglets and blade sweep on HAWTs have typically not considered complex inflow conditions such as turbulent wind and shear. The reasons may include the absence of modeling capability, the computational cost associated with simulating long turbulent time series, and/or the computational cost associated with resolving the blade tips to a very fine level. A preliminary study is performed here, where the MIRAS code is applied on the NREL 5MW wind turbine with an arbitrary winglet shape and blade sweep. Results indicate that wind turbine blades with sweep or winglets might be better in performance compared to their straight blade counterparts.

Modern wind turbine aero-structural blade design codes generally use a smaller fraction of the full design load base (DLB) or neglect turbulent inflow as defined by the International Electrotechnical Commission standards. The current article describes an automated blade design optimization method based on surrogate modeling that includes a very large number of design load cases (DLCs) including turbulence. In the present work, 325 DLCs representative of the full DLB are selected based on the message-passing-interface (MPI) limitations in Matlab. Other methods are currently being investigated, e.g. a Python MPI implementation, to overcome the limitations in Matlab MPI and ultimately achieve a full DLB optimization framework. The reduced DLB and the annual energy production are computed using the state-of-the-art aero-servo-elastic tool HAWC2. Furthermore, some of the interior dimensions of the blade structure are optimized using the finite-element based cross-sectional analysis tool BECAS. The optimization framework is applied to redesign the NREL 5 MW wind turbine blade to obtain improvements in rotor performance and blade weight.

In this paper, four noise propagation models including the parabolic-equation based WindSTAR model, ray-tracing based Nord2000 model, Danish regulation BEK 135 model and ISO 9613-2 standard model are validated against flow and acoustic measurements of a sound source created from a speaker located at a turbine hub of 109 m height. The flow was measured with a fully instrumented met-mast at 350 m and 218 degrees from the turbine tower base. The sound was measured with 11 microphones: 8 were along a line of 45 degrees and a distance up to 1200 m away from the sound source, 3 were located at IEC positions, and 1 microphone close to the speaker, which was used to measure the source strength. White noise and 1/1 band-limited white noise sound at 2 different wind shears with exponents of 0.12 and 0.23 are used for validation. Results show that an overall agreement between experiment and computation is reached for all the numerical models. Among the 4 numerical models, Nord2000 gives the best prediction for the nearfield microphones of mic 4-mic 6 and WindSTAR gives the best prediction for the far-field microphones of mic 7 and mic 8.