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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / NUMERICAL design optimization provides a powerful tool that assists designers in improving their products. Design optimization automatically modifies important design parameters to obtain the best product that satisfies all the design requirements. This thesis explores the use of Support Vector Regression (SVR) and demonstrates its usefulness in the numerical optimization of a low-speed wind turbine for the power coe cient, Cp. The optimization design problem is the three-dimensional optimization of a wind turbine blade by making use of four two-dimensional radial stations. The candidate airfoils at these stations are selected from the 4-digit NACA range. A metamodel of the lift and drag coe cients of the NACA 4-digit series is created with SVR by using training points evaluated with XFOIL software. These SVR approximations are used in conjunction with the Blade Element Momentum theory to calculate and optimize the Cp value for the entire blade. The high accuracy attained with the SVR metamodels makes it a viable alternative to using XFOIL directly, as it has the advantages of being faster and easier to couple with the optimizer. The technique developed allows the optimization procedure the freedom to select profiles, angles of attack and chord length from the 4-digit NACA series to find an optimal Cp value. As a result of every radial blade station consisting of a NACA 4-digit series, the same lift and drag metamodels are used for each station. This technique also makes it simple to evaluate the entire blade as one set of design variables. The thesis contains a detailed description of the design and optimization problem, the implementation of the SVR algorithm, the creation of the lift and drag metamodels with SVR and an alternative methodology, the BEM theory and a summary of the results.

The principal objective of the proposed CFD analysis is to investigate the flow field around a horizontal axis wind turbine rotor and calculate the turbine's power. A full three dimensional computational fluid dynamics method based on Reynolds Averaged Navier Stokes approach was used in this study. The wind turbine has three blades and a rotor diameter of six meters. One third of the wind turbine rotor was modeled by means of 120o periodicity in a moving reference frame system. The power coefficient curve obtained from the CFD results is compared with experimental data obtained by NREL Phase VI rotor experiment. The numerical result for the power coefficient curve shows close agreement with the experimental data. The simulation results include the velocity distribution, pressure distribution along the flow direction, turbulent wake behind the wind turbine, and the turbine's power. The discussion will also include the effect of wind speed on turbine's power. / by Armen Sargsyan. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Small scale wind turbines operating in an urban environment produce dismal amounts of power when compared to their expected output [1-4]. This is largely due to the gusty wind conditions found in an urban environment, coupled with the fact that the wind turbines are not designed for these conditions. A new concept of a Segmented Variable Pitch (SVP) wind turbine has been proposed, which has a strong possibility to perform well in gusty and variable wind conditions. This dissertation explains the concept of a SVP wind turbine in more detail and shows analytical and experimental results relating to this concept. Also, the potential benefits of the proposed concept are mentioned. The results from this dissertation show that this concept has potential with promising results on possible turbine blade aerofoil configurations. Scaled model tests were completed and although further design optimisation is required, the tests showed good potential for the SVP concept. Lastly a proof-of-concept full scale model was manufactured and tested to prove scalability to full size from concept models. Along with the proof-of-concept full scale model, a wireless control system (to control the blade segments) was developed and tested.

To maximize the effectiveness of the rapidly increasing capacity of installed wind energy resources, new models must be developed that are capable of more nuanced control of each wind turbine so that each device is more responsive to inflow events. Models used to plan wind turbine arrays and control behavior of devices within the farm currently make questionable estimates of the incoming atmospheric flow and update turbine configurations infrequently. As a result, wind turbines often operate at diminished capacities, especially in arrays where wind turbine wakes interact and inflow conditions are far from ideal. New turbine control and wake prediction models must be developed to tune individual devices and make accurate power predictions. To that end, wind tunnel experiments are conducted detailing the turbulent flow in the wake of a wind turbine in a model-scale array. The proper orthogonal decomposition (POD) is applied to characterize the spatial evolution of structures in the wake. Mode bases from distinct downstream locations are reconciled through a secondary decomposition, called double proper orthogonal decomposition (DPOD), indicating that modes of common rank in the wake share an ordered set of sub-modal projections whose organization delineates underlying wake structures and spatial evolution. The doubly truncated basis of sub-modal structures represents a reduction to 0.015% of the total degrees of freedom of the wind turbine wake. Low-order representations of the Reynolds stress tensor are made using only the most dominant DPOD modes, corrected to account for energy excluded from the truncated basis with a tensor of constant coefficients defined to rescale the low-order representation of the stresses to match the original statistics. Data from the wind turbine wake are contrasted against simulation data from a fully-developed channel flow, illuminating a range of anisotropic states of turbulence. Complexity of flow descriptions resulting from truncated POD bases is suppressed in severe basis truncations, exaggerating anisotropy of the modeled flow and, in extreme cases, can lead to the loss of three dimensionality. Constant corrections to the low-order descriptions of the Reynolds stress tensor reduce the root-mean-square error between low-order descriptions of the flow and the full statistics as much as 40% and, in some cases, reintroduce three-dimensionality to severe truncations of POD bases. Low-dimensional models are constructed by coupling the evolution of the dynamic mode coefficients through their respective time derivatives and successfully account for non-linear mode interaction. Deviation between time derivatives of mode coefficients and their least-squares fit is amplified in numerical integration of the system, leading to unstable long-time solutions. Periodic recalibration of the dynamical system is undertaken by limiting the integration time and using a virtual sensor upstream of the wind turbine actuator disk in to read the effective inflow velocity. A series of open-loop transfer functions are designed to inform the low-order dynamical system of the flow incident to the wind turbine rotor. Validation data shows that the model tuned to the inflow reproduces dynamic mode coefficients with little to no error given a sufficiently small interval between instances of recalibration. The reduced-order model makes accurate predictions of the wake when informed of turbulent inflow events. The modeling scheme represents a viable path for continuous time feedback and control that may be used to selectively tune a wind turbine in the effort to maximize power output of large wind farms.

The typical methodology for analytically designing a wind turbine blade is by means of blade element momentum (BEM) theory, whereby the aerofoil angle of attack is optimized to achieve a maximum lift-to-drag ratio. This research aims to show that an alternative optimisation methodology could yield better results, especially in gusty and turbulent wind conditions. This alternative method looks at increasing the aerofoil Reynolds number by increasing the aerofoil chord length. The increased Reynolds number generally increases the e_ectiveness of the aerofoil which would result in a higher or similar lift-to-drag ratio (even at the decreased angle of attacked require to maintain the turbine thrust coe_cient). The bene_t of this design is a atter power curve which causes the turbine to be less sensitive to uctuating winds. Also, the turbine has more torque at startup, allowing for operatation in lower wind speeds. This research is assumed to only be applicable to small wind turbines which operated in a low Reynolds number regime (<500 000), where Reynolds number manipulation is most advantageous.

Externally applied loads from high winds or impacts may cause structural damage to the wind-turbine blade, and this may further affect the aerodynamic performance of the blade. Wind-turbine blades experience high vibration levels or amplitudes under high winds. Vibrations negatively affect the wind flow on the blade. This project considers the structural dynamic analysis of a small-scale wind turbine with a particular focus on the blade; it involves the finite element model development, model validation and structural analysis of the validated model. The analysis involves a small-scale wind-turbine structural response when subjected to different loading inputs. The analysis is specifically focused on on-shore systems. The use of small-scale wind-turbine systems is common however, apart from initial structural analysis during design stages, these systems have not been studied sufficiently to establish their behaviour under a variation of real-life loading conditions. On-shore wind turbines are often designed for low-wind speeds and their structural strength may be compromised. In addition, these systems experience widely-varying wind speeds from one location to another to an extent that it is extremely difficult to achieve a uniform structural performance. The main reason for solving this problem is to evaluate the structural response of the blade, with special emphasis on an 800 W Kestrel e230i. This involves the calculation of the distribution of blade deflections and stresses over the wind-turbine blade under different loading conditions. To solve the problem, a three-dimensional model of a Kestrel e230i blade was firstly developed in Autodesk Inventor Professional using geometrical measurements that were taken in the mechanical engineering laboratory. A 3D finite element model was developed in ANSYS using approximate material properties for fiberglass obtained from the literature. The model was then validated by comparing its responses with those from a number of static tests, plus a simple impact test for comparison of the first natural frequency. Finally, a number of numerical tests were conducted on the validated finite element model to determine its structural responses. The purpose of the numerical analysis was to obtain the equivalent von Mises stress and deformation produced in the blade. It was determined that under the examined different loading conditions, a higher stress contour was found to occur around the mid-span of the blade. The calculated maximum flexural stress on the blade was observed to be less than the allowable flexural stress for fiberglass which is 1,770 MPa. As expected, the highest deformation occurred at blade tip. The first critical speed of the assembled three-bladed wind turbine was found to be at 4.3 rpm. The first mode shape was observed to be in the flap-wise bending direction and for a range of rotor speeds between zero and 608 rpm, three out of a total of five mode shapes were in the flap-wise bending direction. Future studies should address issues relating blade vibrations with generated power, validation of dynamic tests, fluid-structural interaction and introduction of bio-inspired blade system. Although the performance of the bioinspired blade has not been studied in great detail, preliminary studies indicate that this system has a superior performance. / Mechanical and Industrial Engineering / M. Tech. (Electrical and Mining Engineering)

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / The aerodynamic performance of an existing wind turbine blade optimised for low wind speed conditions is investigated. The aerodynamic characteristics of four span locations are determined from surface pressure measurements and wake surveys with a traversed five-hole probe performed in a low speed wind tunnel for chord Reynolds numbers ranging from 360,000 - 640,000. Two-dimensional modelling of the wind tunnel tests is performed with the commercial computational fluid dynamics code FLUENT. The predictive accuracies of five eddy-viscosity turbulence models are compared. The computational results are compared to each other and experimental data. It is found that agreement between computational and experimental results varies with turbulence model. For lower Reynolds numbers, the Transitional-SST turbulence model accurately predicted the presence of laminar separation bubbles and was found to be superior to the fully turbulent models considered. This highlighted the importance of transitional modelling at lower Reynolds numbers. With increasing angles of attack the bubbles were found to move towards the leading edge and decrease in length. This was validated with experimental data. For the tip blade section, computations implementing the k-ε realizable turbulence model best predicted experimental data. The two-dimensional panel method code, XFOIL, was found to be optimistic with significantly higher lift-to-drag ratios than measured. Three-dimensional modelling of the rotating wind turbine rotor is performed with the commercial computational fluid dynamics code NUMECA. The Coefficient of Power (Cp) predicted varies from 0.440 to 0.565 depending on the turbulence model. Sectional airfoil characteristics are extracted from these computations and compared to two-dimensional airfoil characteristics. Separation was found to be suppressed for the rotating case. A lower limit of 0.481 for Cp is proposed based on the experimental data. / Centre for Renewable and Sustainable Energy Studies

This thesis presents a complete method of modeling the autospectra of turbulence in closed form via an expansion series using the von Kármán model as a basis function. It is capable of modeling turbulence in all three directions of fluid flow: longitudinal, lateral, and vertical, separately, thus eliminating the assumption of homogeneous, isotropic flow. A thorough investigation into the expansion series is presented, with the strengths and weaknesses highlighted. Furthermore, numerical aspects and theoretical derivations are provided. This method is then tested against three highly complex flow fields: wake turbulence inside wind farms, helicopter downwash, and helicopter downwash coupled with turbulence shed from a ship superstructure. These applications demonstrate that this method is remarkably robust, that the developed autospectral models are virtually tailored to the design of white noise driven shaping filters, and that these models in closed form facilitate a greater understanding of complex flow fields in wind engineering. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

Thesis (MScEng (Department of Mechanical and Mechatronic Engineering))--Stellenbosch University, 2006. / ENGLISH ABSTRACT: Wind conditions in South Africa determine the need for a small-scale wind turbine to produce useable power at windspeeds below 7m/s. In this project, a range of windspeeds, within which optimal performance o the wind turbine is expected, was selected. The optimal performance was assessed in terms of the Coefficient of Power(Cp), which rates the turbines blade's ability to extract energy form the avalible wind stream. The optimisation methods employed allowed a means of tackling the multi-variable problem such that the aerodynamic characteristics of the blade were ideal throughout the wind speed range. The design problem was broken down into a two-dimensional optimisaion of the airfoils used at the radial stations, and a three-dimensional optimisation of the geometric features of the wind rotor. by means of blending various standard airfoil profiles, a new profile was created at each radial station. XFOIL was used for the two-dimensional analysis of these airfoils. Three-dimensional optimisn involved representation of the rotor as a simplified model and use of the Blade Element Momentum(BEM) method for analysis. an existimg turbine blade, on which the design specifications were modelled, was further used for comparative purposes throughout the project. The resulting blade design offers substantial improvements on the reference design. The application of optimisation methods has successfully aided the creation of a wind turbine blade with consistent peak performance over a range of design prints. / Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University