Ducted wind turbine design and investigation of the effects of duct profile to the design with cfd analysis

In the recent researchs, there are many studies to design the wind turbine and to increase the energy that can be generated by wind turbines. These studies are mostly for design purposes and aim at ensuring that the wing geometry can draw more energy from the wind. However, from past to the present days, there are more innovative studies about the ways to improve the performance of the wind turbines and increase the obtained energy output from wind turbines. In this thesis study, examinations have been carried out for this purpose. In this context, studies have been carried out to design a wind turbine with a small rotor diameter and to improve the performance of the designed wind turbine model, a duct geometry was encircled around the wind turbine rotor. For this purpose, firstly the wind geometry was designed by using the wing element theory and momentum disc theory for optimal design parameters in accordance with the determined design conditions. In this phase, the wing angle and wing profile width data which allow the identification of the wing geometry were derived from the Betz wing theory and Schmitz wing theory. At the designation of these data, aerodynamic analyzes of the profiles that selected from the NREL airfoil profile families were used in accordance with the design requirements for blade root, blade tip and main blade body profiles. In the acquisition of the wing design, QBlade software was used to obtain the first predictions for the performance of the wind turbine by two dimensional analysis using lifting line theory via QBlade software. Three dimensional modeling of the wing geometry, where geometrical coordinates of geometry was obtained from QBlade, was created by CATIA modelling program. Further the mesh grid structure was modeled using the ICEM module of the ANSYS 16.0 program for the created analysis domains. Moreover computational fluid dynamics (CFD) analyzes were performed using ANSYS FLUENT module. Analyzes were carried out as fixed free flow regime volume and rotational volume around the frozen rotor geometry. In addition, flow volumes to be analyzed were constructed in accordance with the periodic analysis structure and were arranged to take one wing geometry within the analysis domains. Furthermore k-omega STT model was selected as the turbulence model and the results were obtained by using the method of creating the rotational flow volume around the stationary frozen rotor. Wind velocity and rotational domain angular velocity values were used as a analysis initial inputs. In addition to these, in order to obtain more accurate results around the wing geometry, a separate rotational flow volume is defined and the structural mesh model in O-grid form was used for this flow volume. Also, boundary layer quality of mesh structure around wing was espacially paid attention to obtain more accurate results. As investigated results, the power generation curve and power coefficent curve depending on the blade tip speed ratio, which indicates the performance characteristics.of the wind turbine, was obtained with respect to changing wind velocity. It has been seen that the results obtained from QBlade software as a first prediction in the design phase and CFD results that have been acquired, show similar trends if comparedto each other. The power coefficient curve characterizing wind turbine performance has been found to be consistent with the results shared in reference literature studies. In the course of the proceeding, the thesis' main focus on the design of the wind turbine within the duct to improve the performance of the designed wind turbine. In this direction, 6 point controlled Bezier curves theory was used to determine the design duct profile and closed duct profiles were created with the help of MATLAB code where this theory was embedded. Two dimentional CFD anaysis of randomly created duct profiles have been carried out by DFDC software which is also embedded in the MATLAB code. Furthermore, genetic algorithm multi-objective optimization analysis were performed by using optimization module from Matlab program. In this stage, the design parameters determined at the time of obtaining the wind turbine rotor geometry and the aerodynamic characteristics of the blade profiles were also applied as the analysis inputs and the pareto solution sets were obtained by assigning the maximum power and minimum thrust as optimization target parameters. The solution sets were obtained by generating profiles within the boundaries of the specified control points in order to allow the analysis to proceed smoothly for different approach methods in GAO parameters. In addition, heroustic, random and intermediate crossover approach methods were used for obtainin GAO analysis results. In the optimization, analysis population selected as default value of 200 and generation selected as 50 to generate pareto optimal solution sets. In order to examine the duct geometry and the effects of design parameters for a ducted wind turbine in detail, duct profiles were selected from the solution set which was obtained by intermediate crossover approach method. The effects of selected duct profiles on the performance of the wind turbine were obtained by performing analysis of the computational fluid dynamics for the determined design parameters. For CFD analysis of ducted wind turbine models, again k-omega SST turbulent model was used with frozen rotor model. Furthermore, the analysis results have been obtained for different designs such as the ratio between the duct and the wings, the position of the rotor within the duct geometry, the ratio between the inlet and outlet flow areas, and the use of the partial channel model, and data obtained have been compared comparatively. It can be concluded that the results of CFD analysis for two profiles that selected from different regions within the pareto optimal solution set and results that have been given by DFDC software are close to each other for optimal design conditions. However, it is seen that the design parameters examined also affect the flow around the duct and wing as much as the result, and the performance of the wind turbine also changes depending on this effect. As a supporting result, the analysis of the ratio between the duct geometry and the wings showed very close results for the power output data obtained from the wind turbine. On the contrary, when the results were examined, it has been observed that the increase of the clearence ratio leads to the formation of the flow separation toward the duct wall through outlet and the formation of more wider vortex field at the duct outlet. A similar situation has been observed in the analysis of the position of the rotor geometry in the duct geometry. In addition to these cases, there are results with evident change in the power output data obtained from the wind turbine and the change on the flow field around the duct geometry. Furthermore mesh quality check analysis and FLUENT simulation method analysis also performed to obtain detailed data about accuracy of the analysis. More extensive analysis studies on design parameters have been investigated in this thesis.