Simulation of wind turbine wake interaction using the vorticity transport model

The aerodynamic interactions that can occur within a wind farm can result in the constituent turbines generating a lower power output than would be possible if each of the turbines were operated in isolation. Tightening of the constraints on the siting of wind farms is likely to increase the scale of the problem in the future. The aerodynamic performance of turbine rotors and the mechanisms that couple the fluid dynamics of multiple rotors can be most readily understood by simplifying the problem and considering the interaction between only two rotors. The aerodynamic interaction between two rotors in both co-axial and offset configurations has been simulated using the Vorticity Transport Model. The aerodynamic interaction is a function of the tip speed ratio, and both the streamwise and crosswind separation between the rotors. The simulations show that the momentum deficit at a turbine operating within the wake developed by the rotor of a second turbine is governed by the development of instabilities within the wake of the upwind rotor, and the ensuing structure of the wake as it impinges on the downwind rotor. If the wind farm configuration or wind conditions are such that a turbine rotor is subject to partial impingement by the wake produced by an upstream turbine, then significant unsteadiness in the aerodynamic loading on the rotor blades of the downwind turbine can result, and this unsteadiness can have considerable implications for the fatigue life of the blade structure and rotor hub

Simulating the aerodynamic performance and wake dynamics of a vertical-axis wind turbine

The accurate prediction of the aerodynamics and performance of vertical-axis wind turbines is essential if their design is to be improved but poses a signifi cant challenge to numerical simulation tools. The cyclic motion of the blades induces large variations in the angle of attack of the blades that can manifest as dynamic stall. In addition, predicting the interaction between the blades and the wake developed by the rotor requires a high-fi delity representation of the vortical structures within the fl ow fi eld in which the turbine operates. The aerodynamic performance and wake dynamics of a Darrieus-type vertical-axis wind turbine consisting of two straight blades is simulated using Brown’s Vorticity Transport Model. The predicted variation with azimuth of the normal and tangential force on the turbine blades compares well with experimental measurements. The interaction between the blades and the vortices that are shed and trailed in previous revolutions of the turbine is shown to have a signifi cant effect on the distribution of aerodynamic loading on the blades. Furthermore, it is suggested that the disagreement between experimental and numerical data that has been presented in previous studies arises because the blade–vortex interactions on the rotor were not modelled with sufficient fidelity

Modelling the aerodynamics of vertical-axis wind turbines in unsteady wind conditions

Most numerical and experimental studies of the performance of vertical-axis wind turbines have been conducted with the rotors in steady, and thus somewhat artificial, wind conditions - with the result that turbine aerodynamics, under varying wind conditions, are still poorly understood. The Vorticity Transport Model has been used to investigate the aerodynamic performance and wake dynamics, both in steady and unsteady wind conditions, of three different vertical-axis wind turbines: one with a straight-bladed configuration, another with a curved-bladed configuration and another with a helically twisted configuration. The turbines with non-twisted blades are shown to be somewhat less efficient than the turbine with helically twisted blades when the rotors are operated at constant rotational speed in unsteady wind conditions. In steady wind conditions, the power coefficients that are produced by both the straight- and the curved-bladed turbines vary considerably within one rotor revolution because of the continuously varying angle of attack on the blades and, thus, the inherent unsteadiness in the blade aerodynamic loading. These variations are much larger, and thus far more significant, than those that are induced by the unsteadiness in the wind conditions

Spare Me the Complements: An Immoderate Proposal for Eliminating the "We/They" Category Boundary

A speculative hypothesis about how to eliminate the "we/they" distinction by rearing children (during early critical years) in "aggregates in flux" instead of in kinship-based families: A category cannot be formed from positive examples only: one must be able to sample both what is and what is not in a category in order to recognise the category at all. The basis for the distinction is the features shared by the members (invariants), and absent from the non-members. In "aggregates in flux," the individual members would be constantly varying (and unrelated, genetically). The only invariant would be that they are all human

Opportunité pour l’État du Valais d’implémenter la norme ISO 20022 pour le trafic des paiements

Ce travail de Bachelor consiste en l’étude de l’introduction de la norme ISO 20022 pour l’uniformisation financière auprès de l’État du Valais. Effectivement, à compter de la mi-2018, l’utilisation de cette norme pour le trafic des paiements domestiques en Suisse sera rendue obligatoire. Le mandat de ce travail a été émis par le Centre de Compétences SAP – Finance (CC SAP – Finance) qui cherche à connaître la norme et à étudier la possibilité de l’intégrer dans son système SAP. Pour répondre à ces questions, plusieurs points théoriques liés à la norme ont été développés, tels que le format eXtensible Mark-up Language (XML), les processus concernés et son introduction auprès des institutions financières. Ensuite, la situation actuelle dans le système SAP a été étudiée et la possibilité d’adaptation à la norme a été vérifiée par des tests. Finalement, une synthèse des résultats a permis de proposer des recommandations. L’État du Valais est prêt à utiliser la norme ISO 20022 après configuration et paramétrage du système SAP, nous recommandons cependant de ne pas le faire. Ces recommandations sont principalement justifiées par le fait que le principal partenaire financier de l’État du Valais dans le trafic des paiements, la Banque Cantonale du Valais (BCVs), ne prévoit pas d’adapter son infrastructure avant la fin de l’année 2014 et le début de l’année 2015

Spare Me the Complements: An Immoderate Proposal for Eliminating the "We/They" Category Boundary

A speculative hypothesis about how to eliminate the "we/they" distinction by rearing children (during early critical years) in "aggregates in flux" instead of in kinship-based families: A category cannot be formed from positive examples only: one must be able to sample both what is and what is not in a category in order to recognise the category at all. The basis for the distinction is the features shared by the members (invariants), and absent from the non-members. In "aggregates in flux," the individual members would be constantly varying (and unrelated, genetically). The only invariant would be that they are all human

Synthesis of hydrophilic and hydrophobic carbon quantum dots from waste of wine fermentation

Wine lees are one of the main residues formed in vast quantities during the fermentation of wine. While toxic when applied to plants and wetlands, it is a biodegradable material, and several alternatives have been proposed for its valorization as: dietary supplement in animal feed, source for various yeast extracts and bioconversion feedstock. The implementation of stricter environment protection regulations resulted in increasing costs for wineries as their treatment process constitutes an unavoidable and expensive step in wine production. We propose here an alternative method to reduce waste and add value to wine production by exploiting this rich carbon source and use it as a raw material for producing carbon quantum dots (CQDs). A complete synthetic pathway is discussed, comprising the carbonization of the starting material, the screening of the most suitable solvent for the extraction of CQDs from the carbonized mass and their hydrophobic or hydrophilic functionalization. CQDs synthesized with the reported procedure show a bright blue emission (λmax = 433 ± 13 nm) when irradiated at 366 nm, which is strongly shifted when the wavelength is increased (e.g. emission at around 515 nm when excited at 460 nm). Yields and luminescent properties of CQDs, obtained with two different methods, namely microwave and ultrasound-based extraction, are discussed and compared. This study shows how easy a residue can be converted into an added- value material, thus not only reducing waste and saving costs for the wine- manufacturing industry but also providing a reliable, affordable and sustainable source for valuable materials