Investigation into Boundary Layer Transition on the MEXICO Blade

Lobo, Brandon Arthur; Boorsma, K.; Schaffarczyk, A. P.

doi:10.1088/1742-6596/1037/5/052020

Cited by 10 publications

(6 citation statements)

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“…Within the MexNext project (Boorsma et al, 2018) first comparisons between measurements and simulations were carried out for a rotor model in a wind tunnel. Furthermore, transition was also successfully detected in the experimental data (Lobo et al, 2018), where the growth of T-S disturbances was identified as the main mechanism for the transition process.…”

Section: Introductionmentioning

confidence: 74%

Investigation Into Boundary Layer Transition Using Wall-Resolved LES and Modeled Inflow Turbulence

Lobo

Schaffarczyk

Breuer

2021

Preprint

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Abstract. The objective of the present paper is to investigate the transition scenario of the flow around a typical section of a wind turbine blade exposed to different levels of inflow turbulence. As a first step towards this objective, a rather low Reynolds number of Rec = 105 is studied at a fixed angle of attack but under five different turbulence intensities (TI) up to TI = 11.2 %. Using wall-resolved large-eddy simulations combined with an inflow procedure relying on synthetically generated turbulence and a source-term formulation for its injection within the computational domain, relevant flow features such as the separation bubble, inflectional instabilities and streaks can be investigated. The study shows that the transition scenario significantly changes with rising TI, where the influence of inflectional instabilities due to an adverse pressure gradient decreases, while the influence of streaks increases resulting in a shift from the classical scenario of natural transition to bypass transition. The primary instability mechanism in the separation bubble is found to be inflectional and its origin is traced back to the region upstream of the separation. Thus, the inviscid inflectional instability of the separated shear layer is an extension of the instability of the attached adverse pressure gradient boundary layer observed upstream. The boundary layer is evaluated to be receptive to external disturbances such that the initial energy within the boundary layer is proportional to the square of the turbulence intensity. Boundary layer streaks were found to influence the instantaneous separation location depending on their orientation. A varicose mode of instability is observed on the overlap of the leading edge of a high-speed streak with the trailing edge of a low-speed streak. The critical amplitude of this instability was analyzed to be about 32 % of the free-stream velocity.

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Section: Introductionmentioning

confidence: 74%

Investigation Into Boundary Layer Transition Using Wall-Resolved LES and Modeled Inflow Turbulence

Lobo

Schaffarczyk

Breuer

2021

Preprint

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“…As a part of the MexNext project (Boorsma et al, 2018), transitional studies were carried out on a rotor model in a wind tunnel under varying operating conditions but in the absence of added inflow turbulence. An analysis of the experimental data showed that natural transition of the Tollmien-Schlichting (T-S) kind took place (Lobo et al, 2018). As a part of this project, the first comparisons between CFD (computational fluid dynamics) predictions using turbulence models including transition modeling and such an experiment was conducted by four groups, and a reasonable agreement with the transition location compared to the experimental data was found (Schaffarczyk et al, 2018).…”

Section: Introductionmentioning

confidence: 86%

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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“…This value is set according to the turbulence degree that is present in the experimental conditions for comparison with the simulations. In order to build a relation between the turbulence level and the amplification factor, Mack's expression (Mack, 1977) is used as an estimate.…”

Section: Ellipsys3d Semiempirical E N Transition Modelmentioning

confidence: 99%

“…While the inflow turbulence intensity for an airplane wing in cruise is lower than the one experienced in a wind tunnel, it is higher for rotating machinery or wind turbine rotors (Hernandez et al, 2012). Transition analysis performed for wind tunnel experiments in controlled conditions includes measurements on wind turbine airfoils equipped with pressure taps and sensors, a balance system, and a wake rake (Yilmaz et al, 2017); infrared thermography (Joseph et al, 2016); rotating turbine blade equipped with pressure sensors, strain gauges, a balance system, and particle image velocimetry (Schepers and Snel, 2007); rotating wind turbine; and wind turbine blade experiments by oil visualization, stethoscope, and flush-mounted unsteady pressure sensors (Lobo et al, 2018); and wind turbine airfoil with pressure sensors and high-frequency microphones (Özçakmak et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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

Özçakmak¹,

Madsen

Sørensen³

et al. 2020

Wind Energ. Sci.

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Abstract. Laminar-turbulent transition behavior of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations. The power spectral density (PSD) integrals of the pressure fluctuations obtained from the high-frequency microphones mounted on a blade section are analyzed to detect laminar-turbulent transition locations from the experiments. The atmospheric boundary layer (ABL) velocities and the turbulence intensities (T.I.) measured from the field experiments are used to create several inflow scenarios for the CFD simulations. Results from the natural and the bypass transition models of the in-house CFD EllipSys code are compared with the experiments. It is seen that the bypass transition model results fit well with experiments at the azimuthal positions where the turbine is under wake and high turbulence, while the results from other cases show agreement with the natural transition model. Furthermore, the influence of inflow turbulence, wake of an upstream turbine, and angle of attack (AOA) on the transition behavior is investigated through the field experiments. On the pressure side of the blade section, at high AOA values and wake conditions, variation in the transition location covers up to 44 % of the chord during one revolution, while for the no-wake cases and lower AOA values, variation occurs along a region that covers only 5 % of the chord. The effect of the inflow turbulence on the effective angle of attack as well as its direct effect on transition is observed. Transition locations for the wind tunnel conditions and field experiments are compared together with 2-D and 3-D CFD simulations. In contrast to the suction side, significant difference in the transition locations is observed between wind tunnel and field experiments on the pressure side for the same airfoil geometry. It is seen that the natural and bypass transition models of EllipSys3D can be used for transition prediction of a wind turbine blade section for high-Reynolds-number flows by applying various inflow scenarios separately to cover the whole range of atmospheric occurrences.

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Investigation into Boundary Layer Transition on the MEXICO Blade

Cited by 10 publications

References 0 publications

Investigation Into Boundary Layer Transition Using Wall-Resolved LES and Modeled Inflow Turbulence

Investigation Into Boundary Layer Transition Using Wall-Resolved LES and Modeled Inflow Turbulence

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

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

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