Experimental Study of Wave Forces on an Offshore Wind Turbine Tower Model

study of a tapered wind turbine tower is performed using particle image velocimetry and numerical methods. A 1.5 MW wind turbine base was studied and re-designed. A scaled model of a simple tapered tower base was studied in a wave channel using Particle Image Velocimetry (PIV) to understand the flow phenomena at the tower base. Theoretical and experimental results were found using Morrison equations. The diffraction parameter shows that the linear wave theory is not valid for inertial co-efficient calculations. A direct value of 2.0 resulted for the inertial coefficient values while a lower drag influence was noted at coefficient of drag = 0.315. The turbine’s horizontal force profile is improved in this study to yield a 69% reduction in overturning moment by redesigning the turbines submerged tower

Supercapacitor Parameter Estimation and Hybridyzation with PEMFC for Purge Compensation

This paper focuses on the hybridization of a Proton Exchange Membrane Fuel Cell (PEMFC) and a Supercapacitor to smoothen the voltage disturbance caused by purging in the Fuel Cell. Firstly, a two-branch supercapacitor (SC) model is implemented in Simulink. The parameters of the SC are estimated using Genetic Algorithm Optimization and compared with the classical Faranda method. There is good agreement with the results generated using the Genetic Algorithm Optimization approach. Additionally, experiments were carried out on a 1.2kW PEMFC to acquire the voltage data. Voltage drops during purge were measured and used with the PEMFC model to simulate purge behaviour in the fuel cell. The SC was then connected in parallel to the PEMFC to smoothen the voltage output. The work is still in progress, and so far, positive results have been achieved where the SC has been effective in negating the effects of purge phenomena in PEMFC

Effect of partial blockage of air duct outlet on performance of OWC device

The use of a Savonius rotor as turbine for an oscillating water column (OWC) is demonstrated. The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions. A horizontal turbine section OWC employing a Savonius rotor was tested by varying the opening of OWC exit (0%, 25%, 50%, 75% and 100%) to study the behavior and performance of the device. The OWC model was tested at water depth of 0.29 m at frequencies of 0.8, 0.9 and 1.0 Hz while the exit openings are varied. The static pressure, dynamic pressure, rotational speed of the Savonius rotor and the coefficient of power are presented as results. The OWC with exit opening of 25% showed greater performance in terms of rotational speed and CP compared to OWC with other exit opening percentages. This proves the ability of the OWC to be tuned by regulating flow in the turbine duct

Effect of turbine section orientation on the performance characteristics of an oscillating water column device

Oscillating water column (OWC) devices are the most successful devices for extracting energy from ocean waves. In oscillating water column devices, the air turbine section is of either horizontal or vertical orientation. An experimental study is carried out to compare the airflow characteristics and turbine rpm in horizontal and vertical turbine sections of an oscillating water column device. Two OWC models, one with a horizontal duct connecting the turbine to the atmosphere and the other with a vertical duct, were tested at mean water depths of 230 mm, 260 mm and 290 mm and at frequencies of 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9 Hz, 1.0 Hz and 1.1 Hz. Mean total pressure profiles were plotted just upstream and downstream of the turbine section for different cases, while instantaneous static and dynamic pressure measurements were performed to study their variations with time at these locations. A Savonius type rotor was used as a turbine and its rpm was measured and at the above depths and frequencies to compare the performance of the two OWC models. The OWC model with the horizontal turbine section showed better performance characteristics compared to the OWC with the vertical turbine section. RPM values were 20–30% greater in the horizontal turbine orientation compared to the vertical one. The successful use of a Savonius type rotor as a good and cost-effective option for energy conversion is emphasized in this work

Airfoil optimization for small wind turbines using multi objective genetic algorithm

Small wind turbines are gaining popularity due to their ability to meet community or domestic needs in isolated areas with relatively easier installation and lower cost than large wind turbines. This study looks at optimizing airfoils for use in small horizontal axis wind turbines. The optimization looks to maximize the lift coefficient (Cl ) while minimizing or fixing the drag coefficient (Cd). To satisfy these two objectives a multi–objective genetic algorithm is used. The airfoil is parameterized using a composite Bezier curve with two Bezier segments and 11 control points. Appropriate curvature conditions are implemented at the leading and trailing edge of the airfoil and geometric constraints are applied to maintain the maximum thickness between 8% to 14% of the chord for structural reasons. An existing genetic algorithm (GA) code is modified in C++ to generate suitable airfoils using the 13 control points and pass the coordinates to a solver for analysis. As a result four new airfoils are generated for application in low Reynolds number (Re) flow. The characteristics and suitability of the four airfoils are discussed while comparing them to the popular SG6043 airfoil

Design and optimization of airfoils and a 20 kW wind turbine using multi-objective genetic algorithm and HARP_Opt code

Small wind turbines (SWTs) are ideal for supplying electricity to small remote communities that do not have grid access. However, literature review and trends point out that SWTs are far from fully developed. While larger wind turbines have been researched extensively and perfected, SWTs lack improvements in efficiency and capacity factor. In the present work, airfoil sections for a 20 kW wind turbine were generated using Multi-Objective Genetic Algorithm. The USP07-45XX family of airfoils was designed to achieve maximum lift-to-drag ratio from 4 to 10° angles of attack and to be insensitive to leading edge roughness. The USP07-45XX airfoils showed only slight change during clean and soiled conditions both in experiments and in numerical studies. The optimized airfoils were used in the design of a 20 kW wind turbine. The turbine design and optimization code developed by National Renewable Energy Laboratory (NREL) – HARP_Opt – was used to design and optimize the 20 kW turbine. The turbine was designed using soiled airfoil characteristics of the USP07-45XX family of airfoils. Power curves show cut in speed of 2 m/s and a rated speed of 9 m/s. This gives an annual energy production (AEP) of 4.787 × 104 kWh while having leading edge soiling on blades. The high resistance of the airfoil to soiling means that the AEP will not vary from its design value due to the turbine blades getting dirty or soiled

Experimental studies on the flow characteristics in an oscillating water column device

A fixed type oscillating water column (OWC) device was designed and tested in a 2-D wave channel. The air chamber was converged to its minimum area at the turbine section to obtain the maximum kinetic energy. The variations in the height of water in the water column and in the static pressure of the air caused by the oscillating waves were studied in detail. The airflow in the entire air chamber was documented with particle image velocimetry measurements. No turbine was installed in the device. The experiments were performed by varying the water depth and the wave frequency. It was found that the air velocities in the turbine chamber during the upward motion of water in the column are always larger than during the downward motion. While the airflow was strong most of the time, very low air velocities were recorded during the transition between the upward and downward flows indicating the need of an airflow regulator before the turbine to get a constant flow rate of air. The well-directed flow obtained at the turbine section can be used to drive a Savonius rotor, which is the most appropriate turbine for rectangular cross-section of the chamber

Experimental studies on the flow characteristics in an inclined bend-free OWC device

A bend-free rectangular cross-section OWC device was designed and constructed for studying the effect of inclination on the flow characteristics inside the device. The inclination is meant to reduce reflection of waves and induce higher velocities in the turbine section. Experimental measurements were made in a wave channel where the OWC device was tested. An S-type Pitot tube was used to measure dynamic pressure of air in the turbine section at several inclinations. Particle Image Velocimetry (PIV) was also done to study the flow of both air and water in the OWC device. In order to focus solely on primary energy capture, no turbine was installed in the OWC device. The dynamic pressure readings were analysed for suction and compression stages. Water volume fluctuations inside the capture chamber were also recorded and compared for different inclinations. The result was an increase in the velocity of air flowing in the capture chamber and hence a rise in the kinetic energy available to the turbine. It was found from experimental studies that as the angle of inclination reduced, the velocity of air in the turbine section increased. The lower angles also caused higher run-up and larger volume of water into the capture chamber