A benchmark study on the efficiency of unconstrained optimization algorithms in 2D-aerodynamic shape design

Vorspel, Lena; Schramm, Matthias; Stoevesandt, Bernhard; Brunold, Luca; Bünner, M. J.

doi:10.1080/23311916.2017.1354509

Cited by 4 publications

(8 citation statements)

References 26 publications

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“…The above work does not model the rotation, which is important to get the correct local angle of attack along the blade and thus accurately compute the forces acting on the blade. Several 3-D adjoint-based optimization efforts model rotation effects, three of which studied the NREL Phase VI rotor Dhert et al, 2017;Vorspel et al, 2018), and another which studied the MEXICO rotor (Tsiakas et al, 2018). Economon et al 2013used a continuous adjoint formulation to perform single-point aerodynamic shape optimization using a compressible RANS model.…”

Section: High-fidelity Cfd-based Optimization Using the Adjoint Methodsmentioning

confidence: 99%

Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Madsen¹,

Zahle²,

Sørensen³

et al. 2019

Wind Energ. Sci.

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Abstract. The wind energy industry relies heavily on computational fluid dynamics (CFD) to analyze new turbine designs. To utilize CFD earlier in the design process, where lower-fidelity methods such as blade element momentum (BEM) are more common, requires the development of new tools. Tools that utilize numerical optimization are particularly valuable because they reduce the reliance on design by trial and error. We present the first comprehensive 3-D CFD adjoint-based shape optimization of a modern 10 MW offshore wind turbine. The optimization problem is aligned with a case study from International Energy Agency (IEA) Wind Task 37, making it possible to compare our findings with the BEM results from this case study and therefore allowing us to determine the value of design optimization based on high-fidelity models. The comparison shows that the overall design trends suggested by the two models do agree, and that it is particularly valuable to consult the high-fidelity model in areas such as root and tip where BEM is inaccurate. In addition, we compare two different CFD solvers to quantify the effect of modeling compressibility and to estimate the accuracy of the chosen grid resolution and order of convergence of the solver. Meshes up to 14×106 cells are used in the optimization whereby flow details are resolved. The present work shows that it is now possible to successfully optimize modern wind turbines aerodynamically under normal operating conditions using Reynolds-averaged Navier–Stokes (RANS) models. The key benefit of a 3-D RANS approach is that it is possible to optimize the blade planform and cross-sectional shape simultaneously, thus tailoring the shape to the actual 3-D flow over the rotor. This work does not address evaluation of extreme loads used for structural sizing, where BEM-based methods have proven very accurate, and therefore will likely remain the method of choice.

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Section: High-fidelity Cfd-based Optimization Using the Adjoint Methodsmentioning

confidence: 99%

Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Madsen¹,

Zahle²,

Sørensen³

et al. 2019

Wind Energ. Sci.

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show abstract

“…This is in stark contrast to the efforts using the adjoint method cited below, where up to several hundred design variables are commonly optimized. Interestingly, the findings by Lyu et al (2014) seem to resonate with more recent work from the wind energy community (Vorspel et al, 2017), and both works point to the use of the adjoint method for an efficient gradient computation.…”

mentioning

confidence: 72%

“…Something they expect to change for future rotating blades applications. The briefly cited benchmark paper by Vorspel et al (2017) is indeed also with OpenFOAM but it is kept in 2D. and Tsiakas et al (2018).…”

Section: High-fidelity Optimization Using the Adjoint Methodsmentioning

confidence: 99%

Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Madsen¹,

Zahle²,

Sørensen³

et al. 2018

Preprint

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Abstract. The wind energy industry relies heavily on CFD to analyze new turbine designs. To utilize CFD further upstream the design process where lower fidelity methods such as BEM are more common, requires the development of new tools. Tools that utilize numerical optimization are particularly valuable because they reduce the reliance on design by trial and error. We present the first comprehensive 3D CFD adjoint-based shape optimization of a modern 10&thisp;MW offshore wind turbine. The optimization problem is aligned with a case study from IEA Wind Task 37, making it possible to compare our findings with the BEM results from this case study, allowing us to determine the value of design optimization based on high-fidelity models. The comparison shows, that the overall design trends suggested by the two models do agree, and that it is particularly valuable to consult the high-fidelity model in areas such as root and tip where BEM is inaccurate. In addition, we compare two different CFD solvers to quantify the effect of modeling compressibility and to estimate the accuracy of the chosen grid resolution and order of convergence of the solver. Meshes up to 14 · 106 cells are used in the optimization whereby flow details are resolved. The present work shows that it is now possible to successfully optimize modern wind turbines aerodynamically under normal operating conditions using RANS models. The key benefit of a 3D RANS approach is that it is possible to optimize the blade planform and cross-sectional shape simultaneously, thus tailoring the shape to the actual 3D flow over the rotor, which is particularly important near the root and tip of the blade. This work does not address evaluation of extreme loads used for structural sizing, where BEM-based methods have proven very accurate, and therefore will likely remain the method of choice.

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“…In a previous work, the adjoint optimization in OpenFOAM has been tested against other optimization strategies, like finite differences and Nelder-Mead. The independence from the amount of design parameters was shown there, as well as the applicability for wind energy relevant profiles [17].…”

Section: Introductionmentioning

confidence: 87%

“…The definition of the rotor blade's shape can be done in various ways. It was shown in [17] that the free parametrization, i.e., all numerical grid points are design parameters, is not suitable for optimizing rotor blades. This results from large flow field gradients in the chordwise direction and in the spanwise direction, which transfer to the computed gradient.…”

Section: Gradient Projection and Evaluationmentioning

confidence: 99%

Optimize Rotating Wind Energy Rotor Blades Using the Adjoint Approach

2018

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Wind energy rotor blades are highly complex structures, both combining a large aerodynamic efficiency and a robust structure for lifetimes up to 25 years and more. Current research deals with smart rotor blades, improved for turbulent wind fields, less maintenance and low wind sites. In this work, an optimization tool for rotor blades using bend-twist-coupling is developed and tested. The adjoint approach allows computation of gradients based on the flow field at comparably low cost. A suitable projection method from the large design space of one gradient per numerical grid cell to a suitable design space for rotor blades is derived. The adjoint solver in OpenFOAM is extended for external flow. As novelty, we included rotation via the multiple reference frame method, both for the flow and the adjoint field. This optimization tool is tested for the NREL Phase VI turbine, optimizing the thrust by twisting of various outer parts between 20-50% of the blade length.

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A benchmark study on the efficiency of unconstrained optimization algorithms in 2D-aerodynamic shape design

Cited by 4 publications

References 26 publications

Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Optimize Rotating Wind Energy Rotor Blades Using the Adjoint Approach

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