126 research outputs found
Underling data for "On the wake deflection of vertical axis wind turbines by fixed-pitched blades"
No full textThe repository contains the underlining data for "On the wake deflection of vertical axis wind turbines by pitched blades"
This repository consists of experimental (PIV and force measurements) data in the wake of VAWTs with different blade pitch angles. The measured cases include an isolated VAWT with -10, 0, 10 degree pitch, respectively.
Author contribution:
Ming Huang: Conceptualization; Methodology; Validation; Experimental design; Carrying out the experiment; postprocessing
Yugandhar Vijaykumar Patil: Design assistant; Carrying out the experiment; postprocessing
Andrea Sciacchitano: Conceptualization; Experimental design; Methodology; Validation;
Delphine De Tavernier: Conceptualization
Carlos Simao Ferreira: Conceptualization; Methodology; Validation; Experimental design
</p
Underling data for "On the wake deflection of vertical axis wind turbines by fixed-pitched blades"
No full textThe repository contains the underlining data for "On the wake deflection of vertical axis wind turbines by pitched blades"
This repository consists of experimental (PIV and force measurements) data in the wake of VAWTs with different blade pitch angles. The measured cases include an isolated VAWT with -10, 0, 10 degree pitch, respectively.
Author contribution:
Ming Huang: Conceptualization; Methodology; Validation; Experimental design; Carrying out the experiment; postprocessing
Yugandhar Vijaykumar Patil: Design assistant; Carrying out the experiment; postprocessing
Andrea Sciacchitano: Conceptualization; Experimental design; Methodology; Validation;
Delphine De Tavernier: Conceptualization
Carlos Simao Ferreira: Conceptualization; Methodology; Validation; Experimental design
</p
Metric, proportion and light: modern sacred architecture in Brazil
No full textA pesquisa debruça-se sobre a arquitetura religiosa moderna produzida no Brasil, sua trajetória e seu processo de renovação ao longo do século XX, tendo a luz natural como o protagonista deste espaço e o uso das técnicas de proporcionamento na composição plástica das igrejas como eficazes em mobilizar a percepção humana. O objeto de estudo da presente pesquisa configura-se através da arquitetura religiosa produzida por personagens do Movimento Moderno no Brasil: Oscar Niemeyer, Edgar Guimarães do Valle, Dominikus Böhm, Gottfried Böhm, Adolf Franz Heep, Edgar Oliveira Fonseca, Joaquim Guedes, Hans Broos, Antônio Carlos Farias Pedrosa, Jerônimo Bonilha Esteves, Israel Sancovski e Carlos Alberto Naves. Numa delimitação histórica, restringe-se ao período entre 1940 e 1970, fase de implementação, assimilação e consolidação dos princípios modernos no Brasil. Através do estudo e análise das capelas e igrejas escolhidas, a pesquisa desvenda as formas pelas quais o arquiteto entendeu o conceito luminoso, o problema de medidas e de proporções e como isso se refletiu nas expressões e linguagens que envolvem a arquitetura. Para isso, o trabalho analisa treze obras. Os programas representativos dessa arquitetura a serem estudados serão capelas e igrejas católicas.The research focuses on modern religious architecture produced in Brazil, its history and its process of renewal throughout the twentieth century and the natural light as the protagonist of this space and the use of proportioning techniques in plastic composition of the churches as effective to mobilize human perception. The study object of this research is configured through religious architecture produced by Modern Movement in Brazil characters: Oscar Niemeyer, Edgar Guimarães Valle, Dominikus Böhm, Gottfried Böhm, Adolf Franz Heep, Edgar Oliveira Fonseca, Joaquim Guedes, Hans Broos, Antonio Carlos Farias Pedrosa, Jeronimo Bonilha Esteves, Israel Sancovski and Carlos Alberto Naves. In a historical definition, is limited to the period between 1940 and 1970, the implementation phase, assimilation and consolidation of modern principles in Brazil. Through the study and analysis of the chosen chapels and churches, the research reveals the ways in which the architect got the bright idea, the problem of measurements and proportions and how it was reflected in the expressions and languages that involve architecture. For this, the paper analyzes thirteen works. Representative programs of this architecture to be studied will be chapels and Catholic churches
"Opening up to the Rest of Africa?": Continental Connections and Literary (Dis) Continuities Simao Kikamba\u27s Going Home and Jonathan Nkala\u27s The Crossing
No full textThis article focuses on Simao Kikamba\u27s semi-autobiographical novel Going Home (2005) and Jonathan Khumbulani Nkala\u27s one-man drama The Crossing (2009). Both texts chronicle the odyssey of the refugee author or narrator - in Kikamba\u27s text from Angola and in Nkala\u27s drama from Zimbabwe - to South Africa. I argue that although these works picture the growing transnational texture of the South African national space, this apparent continental connectivity is fraught with new intolerances like xenophobia. Far from displaying a definite break from the hallmarks of South African writing during apartheid, such as a preoccupation with the national and a focus on social commitment, the texts stress a continuation of these characteristics while at the same time re-examining them from a new, Afropolitan angle.
Opsomming Hierdie artikel fokus op Simao Kikamba se semi-outobiografiese roman Going Home (2005) en Jonathan Khumbulani Nkala se eenmandrama The Crossing (2009). Albei tekste vertel die storie van die vlugtelingskrywer of -verteller se tog na Suid-Afrika - in Kikamba se teks vanuit Angola en in Nkala se drama vanuit Zimbabwe. Ek voer aan dat hierdie werke die toenemende transnasionale tekstuur van Suid-Afrika se nasionale ruimte uitbeeld, maar ook dat hierdie klaarblyklik kontinentale samehang deurspek is met nuwe voorbeelde van onverdraagsaamheid, soos vreemdelingehaat. Hierdie tekste beweeg nie onomwonde weg van die onmiskenbare eienskappe van Suid-Afrikaanse skryfwerk gedurende die apartheidsjare nie. (Die eienskappe sluit in \u27n fassinasie met die nasionale en \u27n klem op maatskaplike verantwoordelikheid.) lnteendeel beklemtoon die tekste \u27n voortsetting van die eienskappe, en ondersoek terselfdertyd hierdie eienskappe vanuit \u27n nuwe, Afropolitaanse hoek.
Active Pitch Control of a Vertical Axis Wind Turbine: Enhancing performance in terms of power and loads including dynamic stall effects
No full textDue to its inherent dynamic stability the Vertical Axis Wind Turbine (VAWT) is a strong candidate for large (10-20 MW) floating offshore applications. However, there is room for improvement considering the VAWT’s aerodynamic and structural performance, so as to increase its cost-effectiveness. This thesis explores the VAWT’s potential of enhancing its performance, using active pitch control, in terms of the following three objectives: 1.) power maximization, 2.) power minimization, and 3.) thrust relief. For this purpose the Modified-Linear Actuator Cylinder Model (Mod-Lin ACM) is used as optimization tool. Another inherent feature of the VAWT is that its blades experience large angles of attack, and it is believed that dynamic stall effects will play a significant role in the optimization. The quasi-steady aerodynamic force coefficients in the Mod-Lin ACM are therefore replaced by their dynamic equivalents, which are obtained from a Beddoes-Leishman type dynamic stall model. The phenomenon of leading edge separation is modelled separately, as “plug-in” to this dynamic stall model, following the formulation presented in. The analysis in this work is carried out for the symmetrical NACA0018 airfoil. The achievable increase of maximum power is only 1%, which is even less when unsteady effects are considered in the optimization. For power coefficients at tip-speed ratios and solidities other than the initial optimum point, increases up to 15% are documented. This implies that values close to the initial maximum power can be achieved for lower solidities, decreasing the total weight, and therefore the cost, of the VAWT. A close correlation between the potentials of power increasal and thrust alleviation is found, which is caused by the fact that local power losses due to thrust relief must be compensated on other peripheral positions. Therefore, in order to obtain the highest trust reductions the optimizer will maximize the local power production on the energy efficient parts of the rotor, similar to the power maximization target. Depending on tip-speed ratio and solidity, the given pitch allowance is able to decrease the power production between 65% and 100%. Generally, the decrement is only enhanced by any occurring unsteady effects. This reveals the potential of using the VAWT’s blades as air brake.Aerospace EngineeringAerodynamics, Wind Energy & Propulsion / Wind Energy & DTU Wind EnergyEuropean Wind Energy Master (EWEM
2D Actuator Disk and Vertical Axis Rotor Model in the Wave-Current Unsteady Flow
No full textA cross flow actuator based on a turbine concept is a possible choice for the harvest of the kinetic energy from a dynamic flow. Since there is a large potential of energy contained in the water movement of the ocean, it is fascinating to apply turbines to extract energy. In marine flows, currents can be described as steady since their flow velocities remain unchanged during long periods, while waves are treated as unsteady due to their variation within short periods. In some regions, the flow is a combination of both the current and the wave. Thus, it is interesting to understand how the turbine behaves during the operation in this unsteady flow. The current work tries to model the marine turbines by numerical methods. Two branches are then studied separately. The first model is built within a 2D rotor scale in which the turbine is represented as an actuator disk. Case studies are built with different wave and current velocity scales. The second model studies the case of the Vertical Axis Turbine (VAT) by integrating the wave model with a 2D VAT panel code. The simulation results from the actuator disk model suggest that it is more feasible to extract energy from the case when the current is dominant, while in the other cases, the flow is dominated by the unsteady response with large variations of power or even negative power output observed. The results from the VAT model show that for all the wave current combinations, the turbine can reach a regular periodic performance under the operation condition where the blade rotation period equals the wave period. The further study of the load behavior indicates that the turbine’s response can be controlled by tuning the phase difference between the wave flow and the blade rotation.Applied SciencesSustainable Energy Technolog
Airfoil Optimization for vertical axis wind turbines
No full textThis thesis addresses the process of airfoil optimization for vertical axis wind turbines (VAWT). The airfoils are designed for large scale turbines above 5 MW. The VAWT concept is relevant for offshore floating wind energy, because of its low center of gravity (stability) and their simplicity (low maintenance). An optimal tip speed ratio of 4-4.5 is chosen with an average Reynolds number of 5 million. The solidity c/R of the turbine is 0.1. These operation conditions are representative for the new generation VAWT. The goal of this thesis is to develop an optimization process for VAWT airfoils and to demonstrate it by designing an airfoil, while taking into account airfoil soiling. A literature review presents the previous research in VAWT airfoil design, showing that no consensus has been previously reached about VAWT airfoil design. From the literature review an optimization objective derived by Simão Ferreira [30] is chosen. The airfoil is optimized for aerodynamic and structural performance. The aerodynamics is assessed on airfoil level according to the objective of lift slope over drag. Structurally, the airfoil will be optimized for flapwise bending stiffness. Airfoil soiling is simulated on the airfoil by using turbulent transition. A genetic optimization tool for airfoils coupled with RFOIL, an airfoil analysis tool, is used to generate VAWT airfoils. The objective function values are calculated using the aerodynamic coefficients from RFOIL and the geometric properties of the airfoils. The optimization process is validated by analyzing the results with three different models for full VAWT analysis. These models are: 1) an inviscid panel model coupled with RFOIL, 2) a double wake panel model and 3) a CFD model. Three airfoils resulting from the optimization are tested using the aerodynamic models. The performance of the airfoils validates the objective functions, but performance for the soiled case is not satisfactory. These preliminary findings were presented at the 33rd Wind Energy Symposiumat the AIAA SciTech conference [32], the full paper can be found in appendix B Five different strategies are developed to optimize airfoils. The results are analyzed using a double wake panel model. The optimization strategy in which airfoils are optimized for soiled conditions results in the best performing airfoils. The RK2-27 is a demonstration airfoil resulting from this optimization strategy. The CP of this airfoil for a tip speed ratio of 4 and a solidity of 0.1 is 0.53 in the clean case and 0.45 in the soiled case. This was determined by both the inviscid panel model and the double wake panel model. The RK2-27 has an increased CP compared to the NACA 0018 of 0.04 in the clean case at the design operating conditions. The CP in the soiled case is only 0.02 lower than the NACA 0018. The maximum thickness of the airfoil increased by 50% from 18% to 27%. The RK2-27 has similar aerodynamic performance compared to the traditionally used NACA 0018, while structurally it performs significantly better.Wind EnergyAerospace Engineerin
Numerical Analysis of Horizontal Axis wind turbine with gurney flap using OpenFOAM
No full textAerospace EngineeringAerodynamics, Wind Energy & Propulsio
Aerodynamic response of a twodimensional vertical axis wind turbine to turbulence
No full textThe increasing globalwarming and climate change has boosted research on sustainable energy in the last few decades leading to a lot of research being carried out on wind energy. Wind turbines have played a major role in harvesting wind energy withHorizontal AxisWind Turbines (HAWTs) being the dominant design. However, for urban and offshore applications, Vertical AxisWind Turbines (VAWTs) have been under consideration for a while. VAWTs have some inherent advantages such as no need for a yawingmechanism, easy operation and maintenance, low noise emission, and better potential performance under skewed and unsteady wind conditions. But due to lack of research on VAWTs, they have not been commercialized on a scale which is equal to that of HAWTs. This study is one of such attempts for a better understanding of VAWTs. The primary aim of this study is to explore and analyse the behaviour of VAWTs under the influence of turbulent wind. This target has been achieved by analysing the loads on the turbine and their effect on its fatigue life under the influence of constant wind and turbulent wind. For this purpose, first one hour turbulent wind fields based on statistical models were generated using the turbulence simulator, ‘TURBSIM’ and two-dimensional turbulent wind fields were extracted from the generated wind fields. Next, the simulations of a two-dimensional vertical axis wind turbine using the generated turbulent wind fields were done in an aeroelastic code named ‘Unsteady Two-Dimensional Vorticity Aerodynamics (U2DiVA)model’. These simulationswere done between the cut-in (4 m/s) and cut-out (25 m/s) wind speeds of the turbine at intervals of 1 m/s. The results from these simulations were the streamwise force, cross-streamwise force and the moment about the quarter-chord points of the airfoils of the blades. A post-processing tool was then developed for the processing of these results. Using this tool and the results of the simulations, the equivalent tangential force, the equivalent radial force and the equivalent moment on the airfoilswere calculated. All calculationswere done for both types of wind. First the equivalent loads at each wind speed were calculated and then the total equivalent loads were calculated. The equivalent loads were calculated for various values of inverse slope (m) of the S-N curve of thematerial used to manufacture the blades of the turbine. The same procedure was repeated with constant wind. Finally,the changes in total equivalent loads under turbulent wind were calculated with respect to total equivalent loads under the constant wind. The variation in these changes with respect to the change in the value ofmwas then calculated. Additionally, the effect of phase angle (angle between the blades and the incoming windstream at the beginning of the simulation) on the equivalent loads was also calculated. The value of m used for this case was 10 as recommended in literature and the four phase angles chosen were 0o, 45o, 90o and , 135o.The equivalent loads at various wind speeds were calculated for the different values of m and various peaks were observed at various wind speeds. It was recommended that the peaks can be avoided using a suitable control scheme to control the rotational speed of the rotor. The changes in total equivalent loads under the influence of turbulent wind were found to be less than 0.2% which indicates that the effect of turbulence on the fatigue life of VAWTs is not so significant. The value of m at which the change was smallest was found to be around 3. Under phase effect, the variation of the radial force and the moment with wind speed seemed to follow Gaussian distribution at phase angles of 45o, 90o and 135o. The total equivalent loads were found out for all the phase angles and the change in these loads were found out with respect to 0o phase angle. These changes were quite high and indicate that the operation of a VAWT at phase with incoming wind can be detrimental for the fatigue life of the VAWT.Aerospace EngineeringAerodynamics, Wind Energy & PropulsionSustainable Energy Technolog
The near wake of the VAWT: 2D and 3D views of the VAWT aerodynamics
No full textThe analysis, modeling and design of the lift-driven Vertical Axis Wind Turbine (VAWT) has challenged the wind energy community for many decades; this limited progress in knowledge has severely impaired the development of the VAWT, giving rise to the myth that the VAWT rotor is inherently inefficient (in comparison with the more conventional Horizontal Axis Wind Turbine - HAWT) or too complex for commercial implementation. In this research work, we take a new path on the analysis of the VAWT: instead of considering a rotor that creates a perturbation on the flow (wake and induction field), we consider an unsteady wake, to which a rotor energy-conversion system is associated, obtaining the loading on the blade by better understanding the flow. The research aims at understanding the wake and its relation with energy conversion and the loading on the rotor system. Four main questions drive this research: \u95 What is the relation between blade loading and energy conversion? \u95 How does the near wake of the VAWT develop? \u95 What is the difference between the 2D and the 3D wake? \u95 How does understanding the near wake improve our design? At the end of this dissertation we achieve a clear and insightful view on the 2D and 3D aerodynamics from the point of view of the wake, that significantly improves the aerodynamic design and optimization of new VAWT rotors for energy conversion and propulsion, opening a new design space and methodology. The results and discussion presented in this dissertation are organized in five steps (see thesis outline, Chapter 1): \u95 Part I: understand the fundamental VAWT aerodynamics and how these relate with the research presented in this dissertation. \u95 Part II: understand the energy exchange process in the 2D plane by understanding the shedding of the wake over the rotation, and the wake expansion in 2D. Analyze the impact of dynamic stall on the near wake evolution, and how to extract blade load information from the near wake in dynamic stall. \u95 Part III: understand the impact of the spanwise dimension of the rotor and the role of the consequent trailing vorticity. Investigate the little known skewed flow. \u95 Part IV: understand better the energy exchange process, the wake’s generation and the decoupling between loading and energy conversion. Propose new approaches and guidelines for the aerodynamic rotor design. \u95 Part V: discuss the main results and conclusions of the research, and its impact on new aerodynamic research and design approaches, both for 2D and 3D VAWT rotors. In Part I (Chapter 2) we frame our research approach, analyzing the VAWT from a wake perspective, by considering both 2D and 3D aerodynamics of the VAWT at two different scales: aerofoil/blade scale and rotor scale. We divide the rotor in windward (315? < ? < 45?), upwind (45?< ? < 135?), leeward (135? < ? < 225?) and downwind (225? < ? < 315?) regions of the rotation. This approach obsolesces the conventional division of the rotor into upwind and downwind halves; while the upwind/downwind division is driven by angle of attack considerations (blade loading problem), this new segmentation is determined by the shedding of vorticity (energy conversion problem), a more useful and effective approach. The wake is also split into shed vorticity due to the time gradient of the bound circulation, and trailing vorticity due to the spatial gradient of the bound circulation; this division leads to our 2D and 3D analysis of the flow. In Part II, we analyze the 2D rotor and wake at two scales: rotor and blade. The two flow scales are obviously related, in the sense that the rotor’s aerodynamics are the result of the wakes generated at the several blades and the blade experiences an induction field due to the vorticity distributed over the wake at the rotor scale. The separation in blade and rotor scale is in fact a separation of two views on the total system: \u95 The rotor, as an energy exchange system, where the energy exchange results in a wake and streamline expansion. \u95 The blade, as an aerodynamic loading system, where the design-objective loading is associated with an equivalent bound circulation. The time variation of this bound circulation results in a shed wake. The 2D potential-flow analysis (Chapter 3) shows that: \u95 the conventional breakdown of the VAWT into upwind and downwind actuator systems is incorrect, leading to an overestimation of energy conversion on the upwind half of the rotation and an underestimation in the downwind half. \u95 contrary to the HAWT, the induction is not a function of the total loading, but only of the load component associated with the azimuthally varying circulation. \u95 it is possible to significantly improve Double Multiple Streamtube models by incorporating a better description of the flow. The proposed improved model clearly surpasses conventional models on the prediction of the induction and loading. \u95 the impact of the blade bound-circulation constant-term is small in comparison to the time-varying bound-circulation term; therefore, the induction field of the 2D VAWT in potential flow can be defined by only the number of blades, rotor solidity and tip-speed ratio. This allows for the obsolescence of streamtube momentum models, replaced by faster and more accurate potential flow vortex models. In Chapters 4 and 5 we visualize and quantify, experimentally and numerically, the flow field in the near wake of the blade during the upwind and leeward segments of the motion, at tip-speed ratios ? = 2, 3 and 4, using Particle Image Velocimetry (PIV). An interesting physical aspect of the vortical flow in dynamic stall, especially at low tip-speed ratios, is the transport of the shed vorticity with the blade. This transport of the vortical structures with the blade means that the geometry of the wake, due to viscous effects, differs from what is obtained with potential flow. A different spatial distribution of the shed vorticity implies a different induction field, which might imply a reduction of the effectiveness of momentum models and simple potential-flow models and change the rotor’s performance. The results show two important effects: \u95 At the rotor scale, the transport of vorticity with the blade, rolled in the leading edge/trailing edge separated vortices. \u95 At the blade scale, the importance of the small scale vortices for the oscillations on pressure distribution and loads. In Chapter 6 we use the experimental and numerical data from the previous chapters to evaluate the feasibility of extracting information from the flow/wake measured with PIV, even in dynamic stall, for improving flow analysis and model validation. In Part III we introduce the fourth dimension of our problem: the spanwise direction. The finite span leads to a non-constant spanwise distribution of circulation on the blade, and this distribution leads to the release of trailing vorticity, of which the blade tip vortex is the most prominent component. In Chapter 7 we measure the wake at the tip-vortex region of the VAWT; in Chapter 8 we combine these experimental results with 3D unsteady free-wake potential-flow simulations to: \u95 experimentally and numerically observe, quantify and analyze the generation and convection of the 3D tip vortex of the VAWT. \u95 experimentally, numerically and analytically investigate the effect of blade-tip shape on the generation and convection of the tip vortex, with focus on the added circulation due to the motion of the blade. \u95 combine experimental measurements and numerical simulations to analyze: the 3D wake of the VAWT; the interaction between shed and trailing vorticity; the roll-up and expansion of the wake in the leeward and windward regions; the in-rotor convection and inboard/outboard motion of the tip vortex; the 3D induction field; the 3D blade wake interaction during the downwind blade passage; and the effect of trailing vorticity in the spanwise distribution of circulation, including the 2D to 3D load direction reversal in the downwind blade passage. The spanwise dimension of the flow also gives rise to a new form of misalignment between the flow and the axis: skewed flow. In Chapter 9 we analyze the physics of skewed flow, flow asymmetry, near wake development, blade-wake interaction and impact on energy conversion. The analysis of the VAWT from the point of view of the 2D and 3D near wake is shown to be very effective in understanding: the physics of the flow; the energy exchange process; how the total energy exchange over one rotation actually relates to the local aerodynamic loading on the blade; the impact of implementing an essentially 2D energy conversion process into a 3D aerodynamic system; and the resulting inefficiencies due to the finite span and trailing vorticity. In Part IV (Chapter 10) we show that it is possible to decompose the VAWT design problem into designing for loading and designing for energy conversion, opening a large design space and proposing a new methodology, impacting both 2D and 3D flow. We also show that, although the 2D wake does not vary significantly with variation in the pitching axis location and blade camber, the 3D wake and performance are significantly affected by these variations. This is due to the impact that varying the bound circulation has on the release of trailing vorticity; a larger trailing vorticity generated during the upwind blade passage implies a larger induction due to trailing vorticity, and a worse interaction at the downwind blade passage. The effects of variation of camber and/or pitching axis in 2D and 3D performance are contradictory and complementary and can be simultaneously optimized. In Part V (Chapter 11) we further develop these and other main conclusions, discussing their impact on VAWT aerodynamics. The research here presented implies a break from conventional approaches to the VAWT aerodynamics, allowing for the development of new research and models, both in 2D flow (aerofoil design, rotor energy conversion optimization) and 3D flow (blade and rotor shape, non-uniform flows).Aerodynamics & Wind EnergyAerospace Engineerin
- …
