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Estudo num?rico de um aerogerador projetado com a metodologia BEM e da utiliza??o de um intensificador de pot?nciaBarros, Aide? Am?lia Torres Sampaio 28 August 2017 (has links)
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Previous issue date: 2017-08-28 / A preocupa??o com o efeito estufa e com a degrada??o que o meio ambiente vem sofrendo,
devido a utiliza??o de fontes de energia n?o renov?veis, como os combust?veis f?sseis, tem
despertado um interesse especial na utiliza??o de fontes renov?veis de energia. Diante disso, a
energia e?lica vem se destacando no cen?rio energ?tico atual do Brasil. Os aerogeradores,
respons?veis pela convers?o da energia e?lica em energia el?trica, s?o intensamente estudados,
visto que se busca formas de aumentar a efici?ncia dos mesmos. Uma poss?vel solu??o para o
aumento da pot?ncia de sa?da fornecida pelo aerogerador ? a utiliza??o de difusores flangeados.
A ideia ? gerar um gradiente de press?o, que causaria a passagem de uma maior de massa de ar
a uma maior velocidade, atrav?s do rotor. Como a pot?ncia de sa?da de um aerogerador ?
diretamente proporcional ao cubo da velocidade, a mesma aumentaria. Com isso o presente
trabalho teve como objetivo principal investigar a utiliza??o de um difusor flangeado, acoplado
a um aerogerador de baixa pot?ncia, visando aumento de pot?ncia convertida. Para isso foi
desenvolvido o projeto e a modelagem 3D do rotor de um aerogerador com capacidade de
convers?o de 300 W utilizando o Blade Element Momentum (BEM). Foram realizadas
simula??es num?ricas transientes do escoamento turbulento que age sobre os dom?nios
estudados, empregando um software CFD. Dois modelos diferentes foram consideradas, o
primeiro foi a turbina e?lica envolta sem o elemento intensificador e o segundo com o elemento
intensificador, possibilitando ent?o uma compara??o entre as duas configura??es. Como
objetivo secund?rio efetuou-se compara??es dos resultados num?ricos com os resultados
anal?ticos da metodologia de projeto adotada (BEM), visando identificar se os dados obtidos
atrav?s do projeto (coeficiente de indu??o axial, ?ngulos, triangulo de velocidade) est?o
pr?ximos da solu??o num?rica. Ao final da an?lise dos resultados, foi poss?vel verificar que o
difusor aumenta a velocidade do ar que passa pelo rotor e?lico em aproximadamente 50%,
causando um aumento de cerca 330% da pot?ncia de sa?da. Diferen?as m?ximas na ordem de
10% foram encontradas entre a solu??o anal?tica (obtidas com o BEM) e a solu??o num?rica.
Al?m disso, p?de-se observar que com o aumento da velocidade da massa de ar, e sem o
aumento da velocidade de rota??o, o tri?ngulo de velocidades acaba sendo modificado o que
gera o fen?meno do stall. Por fim foi feita uma nova an?lise, com a velocidade de rota??o
corrigida, onde p?de-se observar que o tri?ngulo de velocidade volta a se estabilizar. / Concerns about the greenhouse effect and the ill-treatment of the environment due to nonrenewable
energy sources, such as fossil fuels, has aroused a special interest in the use of
renewable energy sources, such as wind energy. Wind energy has been standing out in Brazil?s
current energy scenario. The conversion of wind energy into electricity is accomplished with
wind turbines. Wind Turbines, which are responsible for the conversion of wind energy into
electricity, are intensively studied, since they are a powerful system for energy conversion, but
still have a low efficiency when compared to other systems. One way to increase efficiency is
using flanged diffusers in order to create a pressure gradient which would result in a larger flow
of air, in the rotor, at a higher speed. As the output power of a wind turbine is directly
proportional to the velocity, the power would increase. Therefore, the present work investigates
how the use of a flange diffuser coupled to a low power wind turbine can influence its power
output. In order to achieve this objective, the design and 3D modeling of the rotor of a wind
turbine with a conversion capacity of 300W was done using the Blade Element Momentum
(BEM). Transient numerical simulations of the turbulent flow using CFD software were
accoplished. Two different 3D models were considered, the first one was only the wind turbine
and the second was the wind turbine with an element to increase power, thus allowing a
comparison between the two configurations. As a secondary objective, comparisons of the
numerical results with the analytical results of the adopted design methodology (BEM) were
carried out to identify whether the data obtained through the design (axial induction factor,
angles, velocities triangle) are present in the numerical solution. The analysis allowed to verify
that the diffuser increases the velocity of the air, passing through the wind rotor, by
approximately 50%, causing an increase of 330% in the output power. Maximum differences
of about 10% were found between the analytical solution and the numerical solution. In
addition, it was observed that with the increase of the velocity of the mass of air, and without
the increase of the speed rotation, the velocities triangle ends up being modified which
generates the stall phenomenon. Finally, a new analysis was done, with the corrected speed
rotation, where it can be observed that the speed triangle stabilizes.
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Aerodynamika axiálních větrných turbín / Aerodynamics of axial wind turbinesDubnický, Ladislav January 2019 (has links)
Nowadays, the climate change issue is becoming more and more actual in our society. Increase of the average temperature on Earth in a couple of degrees could have catastrophic consequences. One of the possible solutions seems to be renewable energy sources as photovoltaics, biomass of water and wind energy. This thesis deals with the aerodynamics problems of wind energy source. Wind turbines transform kinetic energy of wind to mechanical power. The efficiency is physically limited to 59,26 %, but in reality, it is getting around 45 %. This is caused by three biggest losses inducted in wind turbines as wake losses, losses due to finite number of blades and drag losses. Based on analytical relationships and including these three losses the aerodynamics blade design is conducted. Later, the numerical simulations show higher values of drag and lower values of lift force on airfoil compared to analytical calculation. In fact, percentage deviations are acceptable and to conclude, the numerical analysis was able to relatively accurately simulate force action of free stream velocity on the blade.
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An enhanced and validated performance and cavitation prediction model for horizontal axis tidal turbinesKaufmann, Nicholas, Carolus, Thomas, Starzmann, Ralf 02 December 2019 (has links)
Tidal energy represents a promising resource for the future energy mix. For harnessing tidal currents free stream horizontal axis turbines have been investigated for some years. The acting physics is very similar to the one of horizontal axis wind turbines, with the additional phenomenon of cavitation, which causes performance reduction, flow induced noise and severe damages to the turbine blade and downstream structures.
The paper presents an enhanced semi-analytical model that allows the prediction of the performance characteristics including cavitation inception of horizontal axis tidal turbines. A central component is the well-known blade element momentum theory which is refined by various submodels for hydrofoil section lift and drag as a function Reynolds number and angle of attack, turbine thrust coefficient, blade hub and tip losses and cavitation. Moreover, the model is validated by comparison with comprehensive experimental data from two different turbines.
Predicted power and thrust coefficient characteristics were found to agree well with the experimental results for a wide operational range and different inflow velocities. Discrepancies were observed only at low tip speed ratios where major parts of the blades operate under stall conditions. The predicted critical cavitation number is somewhat larger than the measured, i.e. the prediction is conservative. As an overall conclusion the semi-analytical model developed seems to be so fast, accurate and robust that it can be integrated in a future workflow for optimizing tidal turbines.
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Evaluation of Design Tools for the Micro-Ram Air TurbineVilla, Victor Fidel 01 June 2015 (has links) (PDF)
The development and evaluation of the design of a Micro-Ram Air Turbine (µRAT), a device being developed to provide power for an autonomous boundary layer measurement system, has been undertaken. The design tools consist of a rotor model and a generator model. The primary focus was on developing and evaluating the generator model for the prediction of generator brake power and output electrical power with and without rectification as a function of shaft speed and electrical load, with only basic manufacturer specifications given as inputs. A series of motored generator evaluation test were conducted at speeds ranging from 9,000 to 25,000 rpm for loads varying between 1 and 3.02 Ohms with output power of up to 80 Watts. Results demonstrated that predicted generated power was at or below 3% error when compared to measured results with about 1% uncertainty. A rotor model was also developed using basic blade element theory. This model neglected induced flow effects and was therefore expected to over predict rotor torque and power. A second rotor model that includes induced flow effects, the open source program X-Rotor, was also used to predict rotor power and for comparison to the blade element rotor model results. Both rotor models were evaluated through wind tunnel validation tests conducted on a turbine generator with two different 3.25 in diameter rotors, rotor-1 (untwisted blades) and rotor-2 (twisted blades). Wind tunnel validation test airspeeds varied between 71-110 mph with electrical loads ranging from 1-20 ohms. Results indicated power predictions to be 50-75% higher for the blade element model and 20-30% for X-Rotor results. The blade element rotor model was modified by applying the Prandtl tip-loss factor to approximately account for the induced flow effects; this addition brought predictions much closer to X-Rotor results. Based on the motor-driven generator test results, it is believed that most of the discrepancy in baseline rotor/generator validation test between predicted and observed power generated is due to inaccuracy in the rotor performance modelling with likely contributors to error being induced flow effects, crude section lift/drag modelling, and aero-elastic deformation. It is concluded that the proposed generator model is sufficient although direct torque measurements may be desired and further development of the µRAT design tools should focus on an improved rotor performance model.
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Development of an active pitch control system for wind turbines / F.M. den HeijerDen Heijer, Francois Malan January 2008 (has links)
A wind turbine needs to be controlled to ensure its safe and optimal operation, especially during high wind speeds. The most common control objectives are to limit the power and rotational speed of the wind turbine by using pitch control.
Aero Energy is a company based in Potchefstroom, South Africa, that has been developing and manufacturing wind turbine blades since 2000. Their most popular product is the AE1kW
blades. The blades have a tendency to over-speed in high wind speeds and the cut-in wind speed must be improved. The objective of this study was to develop an active pitch control system for wind turbines. A prototype active pitch control system had to be developed for the AE1kW blades. The objectives of the control system are to protect the wind turbine from over-speeding and to improve start-up performance.
An accurate model was firstly developed to predict a wind turbine’s performance with active
pitch control. The active pitch control was implemented by means of a two-stage centrifugal
governor. The governor uses negative or stalling pitch control. The first linear stage uses a soft spring to provide improved start-up performance. The second non-linear stage uses a hard spring to provide over-speed protection. The governor was manufactured and then tested with the AE1kW blades. The governor achieved both the control objectives of over-speed protection and improved start-up performance. The models were validated by the results.
It was established that the two-stage centrifugal governor concept can be implemented on any
wind turbine, provided the blades and tower are strong enough to handle the thrust forces
associated with negative pitch control. It was recommended that an active pitch control system be developed that uses positive pitching for the over-speed protection, which will eliminate the large thrust forces. Keywords: pitch control, wind turbine, centrifugal governor, over-speed protection, cut-in wind speed, blade element-momentum theory, rotor, generator, stall, feathering. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.
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Development of an active pitch control system for wind turbines / F.M. den HeijerDen Heijer, Francois Malan January 2008 (has links)
A wind turbine needs to be controlled to ensure its safe and optimal operation, especially during high wind speeds. The most common control objectives are to limit the power and rotational speed of the wind turbine by using pitch control.
Aero Energy is a company based in Potchefstroom, South Africa, that has been developing and manufacturing wind turbine blades since 2000. Their most popular product is the AE1kW
blades. The blades have a tendency to over-speed in high wind speeds and the cut-in wind speed must be improved. The objective of this study was to develop an active pitch control system for wind turbines. A prototype active pitch control system had to be developed for the AE1kW blades. The objectives of the control system are to protect the wind turbine from over-speeding and to improve start-up performance.
An accurate model was firstly developed to predict a wind turbine’s performance with active
pitch control. The active pitch control was implemented by means of a two-stage centrifugal
governor. The governor uses negative or stalling pitch control. The first linear stage uses a soft spring to provide improved start-up performance. The second non-linear stage uses a hard spring to provide over-speed protection. The governor was manufactured and then tested with the AE1kW blades. The governor achieved both the control objectives of over-speed protection and improved start-up performance. The models were validated by the results.
It was established that the two-stage centrifugal governor concept can be implemented on any
wind turbine, provided the blades and tower are strong enough to handle the thrust forces
associated with negative pitch control. It was recommended that an active pitch control system be developed that uses positive pitching for the over-speed protection, which will eliminate the large thrust forces. Keywords: pitch control, wind turbine, centrifugal governor, over-speed protection, cut-in wind speed, blade element-momentum theory, rotor, generator, stall, feathering. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.
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Návrh sklopné vrtule pro bezpilotní prostředky / Design of folding propeller for UAVsDítě, Radovan January 2019 (has links)
This master's thesis deals with the design of foldable propeller for UAVs. The design of the foldalble propeller is created based on theory of propellers and also on tha detail ana-lyzis of existing foldalble propellers with similar dimensions. The propeller is then manufac-tured and tested. One of the part of this thesis also describes design of central hub. At the end the methodical procedure of creating foldable propellers is suggested.
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Aerodynamic Characterization of a Tethered RotorJanuary 2019 (has links)
abstract: An airborne, tethered, multi-rotor wind turbine, effectively a rotorcraft kite, provides one platform for accessing the energy in high altitude winds. The craft is maintained at altitude by its rotors operating in autorotation, and its equilibrium attitude and dynamic performance are affected by the aerodynamic rotor forces, which in turn are affected by the orientation and motion of the craft. The aerodynamic performance of such rotors can vary significantly depending on orientation, influencing the efficiency of the system. This thesis analyzes the aerodynamic performance of an autorotating rotor through a range of angles of attack covering those experienced by a typical autogyro through that of a horizontal-axis wind turbine. To study the behavior of such rotors, an analytical model using the blade element theory coupled with momentum theory was developed. The model uses a rigid-rotor assumption and is nominally limited to cases of small induced inflow angle and constant induced velocity. The model allows for linear twist. In order to validate the model, several rotors -- off-the-shelf model-aircraft propellers -- were tested in a low speed wind tunnel. Custom built mounts allowed rotor angles of attack from 0 to 90 degrees in the test section, providing data for lift, drag, thrust, horizontal force, and angular velocity. Experimental results showed increasing thrust and angular velocity with rising pitch angles, whereas the in-plane horizontal force peaked and dropped after a certain value. The analytical results revealed a disagreement with the experimental trends, especially at high pitch angles. The discrepancy was attributed to the rotor operating in turbulent wake and vortex ring states at high pitch angles, where momentum theory has proven to be invalid. Also, aerodynamic design constants, which are not precisely known for the test propellers, have an underlying effect on the analytical model. The developments of the thesis suggest that a different analytical model may be needed for high rotor angles of attack. However, adding a term for resisting torque to the model gives analytical results that are similar to the experimental values. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019
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Stochastic methods for unsteady aerodynamic analysis of wings and wind turbine bladesFluck, Manuel 25 April 2017 (has links)
Advancing towards `better' wind turbine designs engineers face two central challenges: first, current aerodynamic models (based on Blade Element Momentum theory) are inherently limited to comparatively simple designs of flat rotors with straight blades. However, such designs present only a subset of possible designs. Better concepts could be coning rotors, swept or kinked blades, or blade tip modifications. To be able to extend future turbine optimization to these new concepts a different kind of aerodynamic model is needed. Second, it is difficult to include long term loads (life time extreme and fatigue loads) directly into the wind turbine design optimization. This is because with current methods the assessment of long term loads is computationally very expensive -- often too expensive for optimization. This denies the optimizer the possibility to fully explore the effects of design changes on important life time loads, and one might settle with a sub-optimal design.
In this dissertation we present work addressing these two challenges, looking at wing aerodynamics in general and focusing on wind turbine loads in particular. We adopt a Lagrangian vortex model to analyze bird wings. Equipped with distinct tip feathers, these wings present very complex lifting surfaces with winglets, stacked in sweep and dihedral. Very good agreement between experimental and numerical results is found, and thus we confirm that a vortex model is actually capable of analyzing complex new wing and rotor blade geometries.
Next stochastic methods are derived to deal with the time and space coupled unsteady aerodynamic equations. In contrast to deterministic models, which repeatedly analyze the loads for different input samples to eventually estimate life time load statistics, the new stochastic models provide a continuous process to assess life time loads in a stochastic context -- starting from a stochastic wind field input through to a stochastic solution for the load output. Hence, these new models allow obtaining life time loads much faster than from the deterministic approach, which will eventually make life time loads accessible to a future stochastic wind turbine optimization algorithm. While common stochastic techniques are concerned with random parameters or boundary conditions (constant in time), a stochastic treatment of turbulent wind inflow requires a technique capable to handle a random field. The step from a random parameter to a random field is not trivial, and hence the new stochastic methods are introduced in three stages.
First the bird wing model from above is simplified to a one element wing/ blade model, and the previously deterministic solution is substituted with a stochastic solution for a one-point wind speed time series (a random process).
Second, the wind inflow is extended to an $n$-point correlated random wind field and the aerodynamic model is extended accordingly. To complete this step a new kind of wind model is introduced, requiring significantly fewer random variables than previous models.
Finally, the stochastic method is applied to wind turbine aerodynamics (for now based on Blade Element Momentum theory) to analyze rotor thrust, torque, and power.
Throughout all these steps the stochastic results are compared to result statistics obtained via Monte Carlo analysis from unsteady reference models solved in the conventional deterministic framework. Thus it is verified that the stochastic results actually reproduce the deterministic benchmark. Moreover, a considerable speed-up of the calculations is found (for example by a factor 20 for calculating blade thrust load probability distributions).
Results from this research provide a means to much more quickly analyze life time loads and an aerodynamic model to be used a new wind turbine optimization framework, capable of analyzing new geometries, and actually optimizing wind turbine blades with life time loads in mind. However, to limit the scope of this work, we only present the aerodynamic models here and will not proceed to turbine optimization itself, which is left for future work. / Graduate / 0538 / 0548 / mfluck@uvic.ca
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Genetic Algorithm Based Aerodynamic Shape Optimization Of Wind Turbine Rotor Blades Using A 2 D Panel Method With A Boundary Layer SolverPolat, Ozge 01 December 2011 (has links) (PDF)
This thesis presents an aerodynamic shape optimization methodology for rotor blades of horizontal
axis wind turbines. Genetic Algorithm and Blade Element Momentum Theory are implemented
in order to find maximum power production at a specific wind speed, rotor speed
and rotor diameter. The potential flow solver, XFOIL, provides viscous aerodynamic data of
the airfoils. Optimization variables are selected as the sectional chord length, the sectional
twist and the blade profiles at root, mid and tip regions of the blade. The blade sections are
defined by the NACA four digit airfoil series or arbitrary airfoil profiles defined by a Bezier
curve. Firstly, validation studies are performed with the airfoils and the wind turbines having
experimental data. Then, optimization studies are performed on the existing wind turbines.
Finally, design optimization applications are carried out for a 1 MWwind turbine.
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