Laminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computations

Özçakmak, Özge Sinem; Madsen, Helge Aagaard; Sørensen, Niels N.; Sørensen, Jens Nørkær

doi:10.5194/wes-5-1487-2020

Cited by 9 publications

(5 citation statements)

References 44 publications

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“…Wind turbine blade airfoils operate at large Reynolds numbers in highly unsteady conditions (Leishman, 2002), often in a degraded surface state because of soiling and erosion (Sareen et al, 2013). Even over one single rotor revolution, the local turbulent inflow to a blade section can undergo significant changes (Schaffarczyk et al, 2016;Özçakmak et al, 2020;Madsen et al, 2019a). The resulting large disturbances can cause abrupt transitions in otherwise smoothly developing boundary layers, with not yet fully understood consequences (Morkovin, 1985).…”

Section: Physics Unknownsmentioning

confidence: 99%

Grand challenges in the design, manufacture, and operation of future wind turbine systems

Veers¹,

Bottasso²,

Manuel³

et al. 2023

Wind Energ. Sci.

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Abstract. Wind energy is foundational for achieving 100 % renewable electricity production, and significant innovation is required as the grid expands and accommodates hybrid plant systems, energy-intensive products such as fuels, and a transitioning transportation sector. The sizable investments required for wind power plant development and integration make the financial and operational risks of change very high in all applications but especially offshore. Dependence on a high level of modeling and simulation accuracy to mitigate risk and ensure operational performance is essential. Therefore, the modeling chain from the large-scale inflow down to the material microstructure, and all the steps in between, needs to predict how the wind turbine system will respond and perform to allow innovative solutions to enter commercial application. Critical unknowns in the design, manufacturing, and operability of future turbine and plant systems are articulated, and recommendations for research action are laid out. This article focuses on the many unknowns that affect the ability to push the frontiers in the design of turbine and plant systems. Modern turbine rotors operate through the entire atmospheric boundary layer, outside the bounds of historic design assumptions, which requires reassessing design processes and approaches. Traditional aerodynamics and aeroelastic modeling approaches are pressing against the limits of applicability for the size and flexibility of future architectures and flow physics fundamentals. Offshore wind turbines have additional motion and hydrodynamic load drivers that are formidable modeling challenges. Uncertainty in turbine wakes complicates structural loading and energy production estimates, both around a single plant and for downstream plants, which requires innovation in plant operations and flow control to achieve full energy capture and load alleviation potential. Opportunities in co-design can bring controls upstream into design optimization if captured in design-level models of the physical phenomena. It is a research challenge to integrate improved materials into the manufacture of ever-larger components while maintaining quality and reducing cost. High-performance computing used in high-fidelity, physics-resolving simulations offer opportunities to improve design tools through artificial intelligence and machine learning, but even the high-fidelity tools are yet to be fully validated. Finally, key actions needed to continue the progress of wind energy technology toward even lower cost and greater functionality are recommended.

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Section: Physics Unknownsmentioning

confidence: 99%

Grand challenges in the design, manufacture, and operation of future wind turbine systems

Veers¹,

Bottasso²,

Manuel³

et al. 2023

Wind Energ. Sci.

Self Cite

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“…The details of the instrumentation and the sampling frequencies are described by Özçakmak et al (2020). Detailed boundary layer transition analyses were performed in subsequent studies (Madsen et al, 2019;Özçakmak et al, 2019, 2020 by analyzing the DAN-AERO data further and conducting CFD simulations for the 2D and the full rotor flow.…”

Section: Dan-aeromentioning

confidence: 99%

“…The effective angle of attack in the simulations is calculated by the annular averaging of the axial velocity method in order to compare the results with the field experiments. The details of this method and how it is implemented can be found in previous studies (Hansen et al, 1997;Özçakmak, 2020).…”

Section: Urans Full Rotor Simulations For Dan-aero Experimentsmentioning

confidence: 99%

On the laminar–turbulent transition mechanism on megawatt wind turbine blades operating in atmospheric flow

Lobo

Özçakmak²,

Madsen

et al. 2023

Wind Energ. Sci.

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Abstract. Among a few field experiments on wind turbines for analyzing laminar–turbulent boundary layer transition, the results obtained from the DAN-AERO and aerodynamic glove projects provide significant findings. The effect of inflow turbulence on boundary layer transition and the possible transition mechanisms on wind turbine blades are discussed and compared to CFD (computational fluid dynamics) simulations of increasing fidelity (Reynolds-averaged Navier–Stokes, RANS; unsteady Reynolds-averaged Navier–Stokes, URANS; and large-eddy simulations, LESs). From the experiments, it is found that the transition scenario changes even over a single revolution with bypass transition taking place under the influence of enhanced upstream turbulence, for example, such as that from wakes, while natural transition is observed in other instances under relatively low inflow turbulence conditions. This change from bypass to natural transition takes place at azimuthal angles directly outside the influence of the wake indicating a quick boundary layer recovery. The importance of a suitable choice of the amplification factor to be used within the eN method of transition detection is evident from both the RANS and URANS simulations. The URANS simulations which simultaneously check for natural and bypass transition match very well with the experiment. The LES predictions with anisotropic inflow turbulence show the shear-sheltering effect and a good agreement between the power spectral density plots from the experiment and simulation is found in case of bypass transition. A condition to easily distinguish the region of transition to turbulence based on the Reynolds shear stress is also observed. Overall, useful insights into the flow phenomena are obtained and a remarkably consistent set of conclusions can be drawn.

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“…There are several transition models available (for a review see, e.g., Saric et al, 2003;Langtry et al, 2006;Pasquale et al, 2009;Colonia et al, 2017). Some of these are based on the transport equations, such as the γ (Colonia et al, 2017) and γ −Re equation models (Menter et al, 2006;Langtry et al, 2006;Sørensen, 2009;Menter et al, 2015;Langtry et al, 2015); other ones rely on stability analysis, such as the e N method (Smith and Gamberoni, 1956;van Ingen, 1956).…”

Section: Introductionmentioning

confidence: 99%

“…is the rotation speed, u the mean-flow velocity vector projected in the x 1 -x 2 plane, k = (α, β, 0) the wave vector, and the perturbation propagation angle relative to the outer streamline. Giles, 1987;Özçakmak et al, 2020). This transition model does not account for effects of the blade rotation or the threedimensional flow.…”

Section: Introductionmentioning

confidence: 99%

A simplified model for transition prediction applicable to wind-turbine rotors

et al. 2021

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Abstract. This work aims to develop a simple framework for transition prediction over wind-turbine blades, including effects of the blade rotation and spanwise velocity without requiring fully three-dimensional simulations. The framework is based on a set of boundary-layer equations (BLEs) and parabolized stability equations (PSEs), including rotation effects. An important element of the developed BL method is the modeling of the spanwise velocity at the boundary-layer edge. The two analyzed wind-turbine geometries correspond to a constant airfoil and the DTU 10-MW Reference Wind Turbine blades. The BL model allows an accurate prediction of the chordwise velocity profiles. Further, for regions not too close to the stagnation point and root of the blade, profiles of the spanwise velocity agree with those from Reynolds-averaged Navier–Stokes (RANS) simulations. The model also allows predicting inflectional velocity profiles for lower radial positions, which may allow crossflow transition. Transition prediction is performed at several radial positions through an “envelope-of-envelopes” methodology. The results are compared with the eN method of Drela and Giles, implemented in the EllipSys3D RANS code. The RANS transition locations closely agree with those from the PSE analysis of a 2D mean flow without rotation. These results also agree with those from the developed model for cases with low 3D and rotation effects, such as at higher radial positions and geometries with strong adverse pressure gradients where 2D Tollmien–Schlichting (TS) waves are dominant. However, the RANS and PSE 2D models predict a later transition in the regions where 3D and rotation effects are non-negligible. The developed method, which accounts for these effects, predicted earlier transition onsets in this region (e.g., 19 % earlier than RANS at 26 % of the radius for the constant-airfoil geometry) and shows that transition may occur via highly oblique modes. These modes differ from 2D TS waves and appear in locations with inflectional spanwise velocity. However, except close to the root of the blade, crossflow transition is unlikely since the crossflow velocity is too low. At higher radial positions, where 3D and rotation effects are weaker and the adverse pressure gradient is more significant, modes with small wave angles (close to 2D) are found to be dominant. Finally, it is observed that an increase in the rotation speed modifies the spanwise velocity and increases the Coriolis and centrifugal forces, shifting the transition location closer to the leading edge. This work highlights the importance of considering the blade rotation and the three-dimensional flow generated by that in transition prediction, especially in the inner part of the blade.

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Laminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computations

Cited by 9 publications

References 44 publications

Grand challenges in the design, manufacture, and operation of future wind turbine systems

Grand challenges in the design, manufacture, and operation of future wind turbine systems

On the laminar–turbulent transition mechanism on megawatt wind turbine blades operating in atmospheric flow

A simplified model for transition prediction applicable to wind-turbine rotors

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