Latest results from the EU project AVATAR: aerodynamic modelling of 10 MW wind turbines

This paper presents the most recent results from the EU project AVATAR in which aerodynamic models are improved and validated for wind turbines on a scale of 10 MW and more. Measurements on a DU 00-W-212 airfoil are presented which have been taken in the pressurized DNW-HDG wind tunnel up to a Reynolds number of 15 Million. These measurements are compared with measurements in the LM wind tunnel for Reynolds numbers of 3 and 6 Million and with calculational results. In the analysis of results special attention is paid to high Reynolds numbers effects. CFD calculations on airfoil performance showed an unexpected large scatter which eventually was reduced by paying even more attention to grid independency and domain size in relation to grid topology. Moreover calculations are presented on flow devices (leading and trailing edge flaps and vortex generators). Finally results are shown between results from 3D rotor models where a comparison is made between results from vortex wake methods and BEM methods at yawed conditions

Final results from the EU project AVATAR: aerodynamic modelling of 10 MW wind turbines

This paper presents final results from the EU project AVATAR in which aerodynamic models are improved and validated for wind turbines on a scale of 10 MW and more. Special attention is paid to the improvement of low fidelity engineering (BEM based) models with higher fidelity (CFD) models but also with intermediate fidelity free vortex wake (FVW) models. The latter methods were found to be a good basis for improvement of induction modelling in engineering methods amongst others for the prediction of yawed cases, which in AVATAR was found to be one of the most challenging subjects to model. FVW methods also helped to improve the prediction of tip losses. Aero-elastic calculations with BEM based and FVW based models showed that fatigue loads for normal production cases were over predicted with approximately 15% or even more. It should then be realised that the outcome of BEM based models does not only depend on the choice of engineering add-ons (as is often assumed) but it is also heavily dependent on the way the induced velocities are solved. To this end an annulus and element approach are discussed which are assessed with the aid of FVW methods. For the prediction of fatigue loads the so-called element approach is recommended but the derived yaw models rely on an annulus approach which pleads for a generalised solution method for the induced velocities

Assessment and calibration of the γ equation transition model for a wide range of Reynolds numbers at low Mach

The numerical simulation of flows over large-scale wind turbine blades without considering the transition from laminar to fully turbulent flow may result in incorrect estimates of the blade loads and performance. Thanks to its relative simplicity and promising results, the Local-Correlation based Transition Modelling concept represents a valid way to include transitional effects into practical CFD simulations. However, the model involves coefficients to be tuned to match the required application. In this paper, the γ-equation transition model is assessed and calibrated, for a wide range of Reynolds numbers at low Mach, as needed for wind turbine applications. Different airfoils are used to evaluate the original model and calibrate it, whereas a large-scale wind turbine blade is employed to show that the calibrated model can lead to reliable solution for complex three-dimensional flows. The calibrated model shows promising results for both two-dimensional and three-dimensional flows, even if cross-flow instabilities are neglected

Funds of knowledge 2.0: towards digital funds of identity

This article builds on the growing work on Funds of Identity by offering a conceptualisation of identity in relation to Vygotsky's concept of perezhivanie which is then situated within the discourse on digital identities. I also suggest how teachers and researchers could use avatars, digital representations of online users, as an identity text for drawing on and constructing students' Funds of Identity. In order to illustrate this approach, I briefly sketch an ongoing class-based research project called The Avatar Project. Overall, this article reaffirms and develops the argument that the Funds of Identity approach is an evolution of Funds of Knowledge. This thesis is encapsulated in the phrase, digital Funds of Identity: Funds of Knowledge 2.0

"Thinking as someone else" - Using Avatars in teacher education and the challenge to think and act as someone else.

This article discusses an alternative learning project that has been conducted in an online course at a teacher education program from Fall 2012 to Fall 2015. As part of the course, students have to create avatars and think and act as their avatars when faced with educational issues. The project strives to overcome challenges that teacher education programs have to take into account when preparing students to become teachers. A qualitative research study has been conducted in order to find out more about the studentsΓÇÖ thinking and learning in this innovative approach of the online class. Results of the study and the implications for the project will be discussed

Stall-Induced Vibrations of the AVATAR Rotor Blade

In the course of the AVATAR project, partner predictions for key load components in storm/idle conditions separated in two groups. One group showed large loading due to edgewise instability, the other group damped edgewise oscillation and lower load levels. To identify the cause for this separation, the impact of structural and aerodynamic modeling options on damping of stall-induced vibrations is investigated for two simplified operating conditions of a single AVATAR blade. The choice of the dynamic stall model is found to be the primary driver, and is therefore most likely also the reason for previously observed differences in AVATAR storm load predictions. Differences in structural dynamics, mode shapes, structural and dynamic twist, as well as wake model are only secondary in terms of impact on damping. Resolution suffered from failure of system identification methods to extract reliable damping values from various non-linear response simulations

Intercomparison of stratospheric nitrogen dioxide columns retrieved from ground-based DOAS and FTIR and satellite DOAS instruments over the subtropical Izana station

The comparison of observations performed by different techniques and satellite instruments is important. An intercomparison of the stratospheric NO2 derived from ground-based and satellite instruments has been carried out over the Izaña subtropical site. The importance of the use of the effective solar zenith angle when comparing noon measurements with twilight measurements of photochemically active species is highlighted. All instruments show positive trends in NO2 stratospheric column.This publication has been funded by the AVATAR project of the Spanish national funding Agency (MINECO: CGL2014-55230-R ). This work has been carried out in the frame of the NORS (Demonstration Network of Ground-Based Remote Sensing Observations in support of the Copernicus Atmospheric Service) project (funded by the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 284421; http://nors.aeronomie.be/) and has been partially supported by AMISOC project funded by the Spanish national funding Agency (CGL2011-24891)

CFD code comparison for 2D airfoil flows

The current paper presents the effort, in the EU AVATAR project, to establish the necessary requirements to obtain consistent lift over drag ratios among seven CFD codes. The flow around a 2D airfoil case is studied, for both transitional and fully turbulent conditions at Reynolds numbers of 3 × 106 and 15 × 106. The necessary grid resolution, domain size, and iterative convergence criteria to have consistent results are discussed, and suggestions are given for best practice. For the fully turbulent results four out of seven codes provide consistent results. For the laminar-turbulent transitional results only three out of seven provided results, and the agreement is generally lower than for the fully turbulent case

Calibration of the 7—equation transition model for high Reynolds flows at low mach

The numerical simulation of flows over large-scale wind turbine blades without considering the transition from laminar to fully turbulent flow may result in incorrect estimates of the blade loads and performance. Thanks to its relative simplicity and promising results, the Local-Correlation based Transition Modelling concept represents a valid way to include transitional effects into practical CFD simulations. However, the model involves coefficients that need tuning. In this paper, the γ—equation transition model is assessed and calibrated, for a wide range of Reynolds numbers at low Mach, as needed for wind turbine applications. An aerofoil is used to evaluate the original model and calibrate it; while a large scale wind turbine blade is employed to show that the calibrated model can lead to reliable solutions for complex three-dimensional flows. The calibrated model shows promising results for both two-dimensional and three-dimensional flows, even if cross-flow instabilities are neglected