Figure 9 - available via license: Creative Commons Attribution 4.0 International
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Effect of the shed vorticity on the 50 mHz sinusoidal pitch variation above rated conditions (a) on the distribution of the axial induced-velocity variation amplitude at the blade pitch frequency and (b) on the distribution of the axial induced-velocity variation phase at the blade pitch frequency, with respect to the phase of the prescribed pitch time series.
Source publication
With the increase in rotor sizes, the implementation of innovative pitch control strategies, and the first floating solutions entering the market, the importance of unsteady aerodynamic phenomena in the operation of modern offshore wind turbines has increased significantly. Including aerodynamic unsteadiness in blade element momentum (BEM) methods...
Contexts in source publication
Context 1
... corresponding amplitude and phase plots are shown in Fig. 9. As for the pitch step, the BEM lines (with the TUD-VR model for dynamic inflow) accounting or not accounting for shed vorticity in the dynamic stall model have been added, along with those of AWSM with and without shed vorticity. Figure 9a shows how shed vortices tend to slightly reduce the induced-velocity variation amplitude ...
Context 2
... for the pitch step, the BEM lines (with the TUD-VR model for dynamic inflow) accounting or not accounting for shed vorticity in the dynamic stall model have been added, along with those of AWSM with and without shed vorticity. Figure 9a shows how shed vortices tend to slightly reduce the induced-velocity variation amplitude throughout the span, whereas in terms of phase, the no-shed vorticity line shows a larger (i.e. more negative) phase shift coming closer to the BEM predictions. ...
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With the wake effect between different wind turbines, a wind farm generally aims to achieve the maximum energy capture by implementing the optimal pitch angle and blade tip speed ratio under different wind speeds. During this process, the balance of fatigue load distribution is easily neglected because it is difficult to be considered, and, thus, a...
Citations
... Vortex wake models do not have such shortcomings as the wake is modeled explicitly by the trailing and shed vorticity caused by spacial and temporal gradients in the blade-bound vortex. Hence, the wake develops over time and includes the transient effects that, e.g., pitch actuation or gusts have on the induction in the rotor plane (Mancini et al., 2023). The fact that the most recent release of the Aero-Dyn module (v15) (Murray et al., 2017) of the widely used code OpenFAST (Jonkman et al., 2019) includes a liftingline aerodynamic method named OLAF (Shaler et al., 2020) may be seen as confirmation that higher-fidelity methods than BEM are a requirement for certain conditions. ...
To realize the projected increase in worldwide demand for floating offshore wind, numerical simulation tools must capture the relevant physics with a high level of detail while being numerically efficient. This allows engineers to have better designs based on more accurate predictions of the design driving loads, potentially enabling an economic breakthrough. The existing generation of offshore wind turbines is reaching a juncture, where traditional approaches, such as the blade element momentum theory, are becoming inadequate due to the increasing occurrence of substantial blade deflections. QBlade is a tool that includes a higher-fidelity aerodynamic model based on lifting-line theory, capable of accurately modeling such scenarios. In order to enable the simulation of offshore conditions in QBlade and to make use of this aerodynamic capability for novel offshore wind turbine designs, a hydrodynamic module called QBlade-Ocean was developed. In the present work, this module is validated and verified with two experimental campaigns and two state-of-the-art simulation frameworks on three distinct floating offshore wind turbine concepts. The results confirm the implementation work and fully verify QBlade as a tool to be applied in offshore wind turbine simulations. Moreover, a method aimed to improve the prediction of non-linear motions and loads under irregular wave excitation is analyzed in various conditions. This method results in a significant improvement in the surge and pitch degrees of freedom in irregular wave cases. Once wind loads are included, the method remains accurate in the pitch degree of freedom, while the improvements in the surge degree of freedom are reduced. A code-to-code comparison with the industry-designed Hexafloat concept highlights the coupled interactions on floating turbines that can lead to large differences in motion and load responses in otherwise identically behaving simulation frameworks.
... Similarly, Odgaaard et al. (2015) investigated the use of dynamic inflow in Model Predictive Control (MPC) design and found that with the use of dynamic inflow the tower fatigue load could be significantly reduced while almost not influencing the produced energy. However, including inflow dynamics is only part of the challenge, various types of inflow models have varying influence on control and fatigue loads, Mancini et al. (2023). ...
... The BEM method, instead, requires engineering dynamic inflow models to account for wake unsteadiness and it is not clear how these models perform in non-uniform conditions (like those induced by an individual pitch step). Several state-of-the-art dynamic inflow models for BEM have been recently implemented in AM and their relative performance has been compared in detail [13]. The traditional single-constant dynamic inflow model from ECN [1] and the more recent two-constant model from DTU [14] are used in this work to verify their capability to model non-uniform dynamic wake effects. ...
... The observations are in line with previous comparisons of models for similar conditions. [13] This is not, however, the case when comparing the BEM-based simulations with the experimental reference for the case of asymmetrical pitching. When pitching for high to low loads, the new steady loads differ from the simulated ones. ...
Dynamic inflow effects occur due to the rapid change of the rotor loading under conditions such as fast pitch steps. The paper presents a setup suitable for the investigation of those effects for non-axisymmetric rotor conditions, namely individual pitch steps. Furthermore, insights into the relevant phenomena are gathered. An individual pitch control capable model wind turbine is set up in a wind tunnel in order to conduct measurement under controllable conditions. During the execution of the collective and individual pitch steps, the loads and the operational parameters are recorded by the onboard sensors. Meanwhile, simulations engineering aeroelastic codes are run in order to evaluate their accuracy for predicting the relevant phenomena. Results show distinct behaviour of the rotor loads during an individual pitch step, which differs from the loads under collective steps. The free vortex wake simulations are able to predict the turbines’ response satisfactory while the blade element momentum tools show deviations from the measurements. The findings serve as a basis for discussion and future work.
