Wind farm wake recovery: LES and engineering models compared to wind tunnel dataCenturelli, G; Messmer, T; Wagner, M; Umdenstock, H; Quintana, R; Peinke, J
doi: 10.1088/1742-6596/3016/1/012055pmid: N/A
We compare LES and an engineering model to wind tunnel measurements of the wake of two model wind farms with staggered and aligned layouts. LES and measurements agree very well with a global deviation of less than 8% on TI and WS. Most of the differences were localized in the very near wake of the actuator disks, where the turbulence intensity is underestimated of 20-50%, and the region in between the wakes of the tubines columns of the aligned layout, where velocity is underestimated of 7%. The engineering model (TurbOPark) failed to accurately match the wind farm wake. The default TurbOPark underestimates wake recovery in the near-wake and overestimates it in the far-wake, and the turbines’ added turbulence intensity decays too slowly. Tuning the correlation coefficient between wake expansion and turbulence intensity could not gain a good fit of the experimental data.Finally, we use LES to further investigate the recovery of the two wind farms’ wakes. We propose a criterion to identify the wake recovery region for which we calculated wake recovery budgets. We found that single-turbine wake-recovery traits survive much longer downstream of the aligned wind farm, as more space is required for the wakes of turbine columns to merge and recover as a unique entity. This was identified by the horizontal divergence of the Reynolds stresses (∂u′υ′¯/∂y) contributing to recovery up until ∼ 25D downstream the last farm row, while only up until ∼ 5D for the staggered wind farm.
Towards a regional wind farm planning approach: The Wakeness IndexAlonso-De-Linaje, Nicolas Gonzalez; Hahmann, Andrea N.; Peña, Alfredo
doi: 10.1088/1742-6596/3016/1/012050pmid: N/A
Offshore wind energy expansion often involves large wind farms built in close proximity, where inter-farm wake interactions can significantly impact energy production. Numerical weather prediction (NWP) models such as the Weather Research and Forecasting (WRF) model can capture these interactions but are computationally expensive for exploring multiple future scenarios. To address this limitation, we introduce the Wakeness Index (WIX), a simplified yet scalable tool for preliminary regional wind farm planning. Two variants of the WIX are presented: WIXG, which captures basic geometric interactions among wind turbines, and WIXC, which incorporates local wind climatology to improve accuracy. Both variants show strong agreement with WRF-based wind speed deficit results, with correlations of up to 0.93, yet require a fraction of the computational resources and time. Although WIXC offers higher fidelity, it runs at a rate roughly twenty-eight times slower than WIXG, underscoring the trade-off between speed and complexity. This study highlights the applicability of the WIX for rapid scenario assessments, enabling stakeholders to identify optimal spatial layouts for offshore wind farms before engaging into more detailed, resource-intensive simulations. The WIX streamlines the planning process for large-scale offshore wind projects, facilitating sustainable development and efficient utilization of marine space.
Wake of a floating wind turbine model under roll motionDuan, Guiyue; Porté-Agel, Fernando
doi: 10.1088/1742-6596/3016/1/012008pmid: N/A
The development of floating offshore wind turbine (FOWT) technology facilitates the exploration of deep-ocean wind resources. Meanwhile, there are still open questions on how the structural response will affect the performance of floating turbines and wind farms. Based on wind tunnel experiments, this study investigated the effects of roll motion on the wake characteristics of a floating wind turbine model. Various roll dynamics, differing from roll frequency and amplitude (in the ranges of 0 – 4 Hz and 0 – 15°, respectively), were tested and compared. The results showed that roll motion can accelerate wake recovery and increase the wake turbulence intensity of the floating wind turbine. Spectral analyses revealed the wake periodicity imposed by the cyclic roll motions. Wake meandering was found to have a dominant frequency that was the same as the roll frequency, and was enhanced by the roll motion of the turbine, especially in the spanwise direction. As a result, the lateral wake growth rate increased with increasing roll frequency or amplitude, while wake growth in the vertical direction was less affected. The Gaussian wake model was applied to predict the wake of a FOWT in roll motion. The results showed that the model underestimated the wake deficit in all roll cases, and failed to depict the wake shape (especially in cases with relatively high roll frequency or amplitude), highlighting the importance of considering roll dynamics in floating wind turbine wake model development.
Wake Recovery Enhancement with Helix Active Wake Control: Vortex Structures in a Porous Disk Wake Observed in PIV ExperimentsGutknecht, Jonas; Den Berg, Daniel Van; Der Hoek, Daan Van; De Vos, Brian; Harder, Bjorn; Viré, Axelle; Van Wingerden, Jan-Willem
doi: 10.1088/1742-6596/3016/1/012030pmid: N/A
Power losses at waked turbines due to the energy extraction of upstream turbines from the flow pose a major risk to the economic feasibility of wind farms. Helix active wake control has proven its potential to mitigate these wake-induced power losses by accelerating the recovery of the individual turbine wakes. This method leverages individual pitch control to induce a non-uniformly distributed force perturbation that rotates either in a clockwise (CW) or counterclockwise (CCW) direction around the rotor center. This deforms the wake into a helical shape that recovers faster than the wake of a conventionally controlled turbine. The CCW-oriented helix achieves higher power gains than the CW helix. Previous studies have identified a system of counter-rotating vortices to drive the wake recovery enhancement and the difference between CW and CCW helix. Nevertheless, a causal explanation for the creation of these vortices is still pending. This work contributes to understanding their creation by isolating the effect of the helix force perturbation on a symmetric wake from the impact of blade-related features like tip-vortices, hub vortex, or wake swirl. For this purpose, we perform Particle Image Velocimetry (PIV) measurements of a porous disc (PD) model in a wind tunnel. The PD is modified to mimic the helix but does not inherit the blade-related features present in a wind turbine wake. We observe the formation of two counter-rotating vortices in the far wake that deform the wake cross-section into a kidney shape, analogous to the structures present in the wake when helix active wake control is applied to a wind turbine. A conceptual comparison of PD wake and wind turbine wake implies that the wake swirl present in the turbine wake causes asymmetric reactions in several characteristics of the vortex system to changes in the rotational direction of the helix perturbation. Consequently, the dynamic, non-uniform helix perturbation alone is sufficient to activate the governing mechanisms that enhance the wake recovery when using helix active wake control, while blade-related phenomena are not fundamental to the principal processes.
Benchmark Study on Rotor Performance, Wake Dynamics, and Atmospheric Boundary Layers using NREL SOWFA-6 and AMR-WINDDammann, Tim; Dangi, Nirav; Van Wingerden, Jan-Willem; Yu, Wei
doi: 10.1088/1742-6596/3016/1/012034pmid: N/A
Benchmarking numerical models is essential for validating their accuracy and ensuring consistency across simulation platforms. This study presents a comparative benchmark analysis of two widely used Large Eddy Simulation (LES) codes, AMR-WIND and NREL SOWFA-6, focusing on wind turbine rotor performance, wake dynamics, and atmospheric boundary layer (ABL) representation. The evaluation includes an actuator line model (ALM)-based uniform inflow wind turbine simulation and ABL precursors under neutral and unstable conditions. The uniform inflow wake analysis examined differences in wind turbine induction and wake development between the two codes. Additionally, neutral and unstable atmospheric boundary layer precursors were generated for an offshore environment and compared. Results indicate a difference in wake breakdown location between the codes (one contributing factor was the difference in numerical schemes used for the advection terms.) The number of actuator points required for smooth velocity distribution across the rotor was higher for SOWFA-6 than AMR-WIND. In ABL precursors, time-averaged flow fields showed strong agreement, though minor discrepancies in turbulence were observed, particularly in unstable conditions, affecting coherence analysis. The energy distribution across wavenumbers showed a good match between the codes, with slight discrepancies observed in the large and small wavenumber regions. The cutoff wavenumber was found to be similar for both codes. Lateral and vertical coherence at small and large separations were in close agreement for the neutral ABL. However, in the unstable ABL, notable differences in coherence were observed between the codes for separations greater than 40 m.
Design of twist-modified lab-scale wind turbine rotors for enhanced wake recoverySellevold, Viljar Dyvik; Raupach, Felix; Sukhman, Daniel; Bartl, Jan
doi: 10.1088/1742-6596/3016/1/012006pmid: N/A
Enhancing power production in wind farms by improved wake recovery has emerged as a major research focus in recent years. By implementing flow control strategies on turbine rotors, researchers aim to mitigate wake effects and optimize energy output across entire wind farms. The wake-diffusion rotor concept proposed by Equinor deviates from traditional rotor designs by modifying the blades’ radial twist angle distribution. The loading on the inner portion of the rotor blades is intentionally decreased to create additional flow entrainment and shear gradients in the center of the wake.To investigate this, performance and wake flow experiments are conducted on three rotor blade sets, two featuring moderate and radical twist angle modifications, respectively, in a lab-scale experimental campaign. In both cases the inner half of the blades’ radius is de-loaded. The three rotors are mounted to a underwater test turbine equipped with both torque and thrust sensors for performance measurements. The three-dimensional flow field in the wake is captured using a Lagrangian Particle Tracking Velocimetry (LPTV) at several downstream distances of the rotors.Results from initial power and thrust measurements show only minor differences in the three rotors’ power output at their design tip speed ratio. A comparison of the mean components in the wake indicates an improved wake recovery for the two modified rotors. In the near wake the wake diffusion rotors show locally higher mean velocities in the wake center, where additional wake diffusion is initiated. These initial results indicate a promising potential for the concept, while measurements under various inflows and at larger downstream distances are needed to quantify the full potential.
Impact of Scaling on the Performance and Wake Characteristics of Paired Counter-Rotating Vertical Axis Wind TurbineSiddiqui, M S; Kouaissah, O; Franchina, N; Mian, H H; Pettersen, E
doi: 10.1088/1742-6596/3016/1/012047pmid: N/A
This study investigates the aerodynamic performance and wake dynamics of counter-rotating vertical-axis wind turbines (VAWTs) through two-dimensional computational fluid dynamics (CFD) simulations. The analysis focuses on the effects of geometric scaling, wherein the turbine diameter is increased tenfold, leading to a rise in the chord-based Reynolds number from 2.1 × 105 to 2.65 × 106. This transition surpasses the critical threshold of 1.5 × 106, which is associated with marked improvements in aerodynamic efficiency for VAWTs. The results show that, for the baseline configuration, outward-rotating turbines spaced at 1.15D yield the lowest power coefficient. However, at larger scales, the performance at this same spacing improves significantly, indicating that higher Reynolds numbers may mitigate adverse wake interactions and enable more compact turbine arrays. A consistent increase of approximately 21% in power coefficient is observed for spacings ≥ 1.25D between the baseline and scaled models. Furthermore, the study indicates that outward rotation at an azimuthal offset of β = 60° outperforms inward rotation, maintaining superior torque and aerodynamic efficiency across scales. Wake structure analysis reveals that scaled turbines produce more centralized vorticity and reduced wake velocity deficits, which suggests enhanced kinetic energy extraction and a more streamlined wake profile. Overall, the results demonstrate the potential of turbine scaling to improve VAWT performance and inform the design of more efficient wind farm configurations.
Validation of WRF-Simulated North Sea Wind Fields: A Comparative Analysis with Observations at LEG and EPL PlatformsVimalakanthan, Kisorthman; Bot, Edwin; Engels, Wouter
doi: 10.1088/1742-6596/3016/1/012053pmid: N/A
This study evaluates the Weather Research and Forecasting (WRF) model’s ability to simulate wind fields in the North Sea, using lidar data from the Europlatform (EPL) and Lichteiland Goeree (LEG) platforms. Three nested domain configurations with increasing resolution (18 km to 0.5 km) were tested over a 23-day period to assess spatial and temporal resolution impacts. Case 0 (18/6/2 km), Case 1 (9/3/1 km), and Case 2 (3/1.5/0.5 km) used the MYNN planetary boundary layer scheme and Fitch wind farm parameterization. Case 2 showed the strongest agreement with observed wind speed (correlation: 0.87–0.88) and direction (0.88). Wake impact analysis highlighted strengths and limitations in WRF’s representation of wind farm effects. All cases captured the peak in wind speed ratio (ΔWSR) around 200°–250°, where LEG is primarily affected by the wake, with Case 0 aligning best with observations.
Identifying Wake Patterns in Weather Regimes over the Southern Bight of the North Sea using clustering techniquesPalatos-Plexidas, Alexandros; De Paepe, Geert; Bonnefoy, Lars; Gremmo, Simone; Van Beeck, Jeroen; De Cruz, Lesley; Munters, Wim
doi: 10.1088/1742-6596/3016/1/012046pmid: N/A
In this study, we seek to bridge the global-scale weather regimes and the wind farm wake effects at the regional level, aiming to identify the influence of different circulation types on wake propagation. For this purpose, we use a two-step numerical approach. Initially, we use a mesoscale numerical weather prediction model to calculate the wind farm-produced wind speed deficits over three years, 2021, 2022, and 2023. Subsequently, we identify weather regimes using the ERA20C global reanalysis dataset from the ECMWF, covering a period from 1900 to 2010. A deep-learning-based dimensional reduction method is trained and validated on this long dataset, yielding a low-dimensional representation in which clusters corresponding to different weather regimes can be identified. The ERA5 dataset (1940-present) is additionally utilized to provide the weather regimes over the same period as the regional model. This exploratory study suggests that the different circulation types result in different wake patterns and varying wind farm power production in the Southern bight of the North Sea.