Identification of variations of angle of attack and lift coefficient for a large horizontal-axis wind turbine

The current paper investigates the effects of various elements including turbulence, wind shear, yawed inflow, tower shadow, gravity, mass and aerodynamic imbalances on variations of angle of attack and lift coefficient for a large horizontal-axis wind turbine. It will identify the individual and the aggregate effect of elements on variations of mean value and standard deviation of the angle of attack and lift coefficient in order to distinguish the major contributing factors. The results of the current study is of paramount importance in the design of active load control systems for wind turbine

Effect of pitch angle on power performance and aerodynamics of a vertical axis wind turbine

Due to growing interest in wind energy harvesting offshore as well as in the urban environment, vertical axis wind turbines (VAWTs) have recently received renewed interest. Their omni-directional capability makes them a very interesting option for use with the frequently varying wind directions typically encountered in the built environment while their scalability and low installation costs make them highly suitable for offshore wind farms. However, they require further performance optimization to become competitive with horizontal axis wind turbines (HAWTs) as they currently have a lower power coefficient (CP). This can be attributed both to the complexity of the flow around VAWTs and the significantly smaller amount of research they have received. The pitch angle is a potential parameter to enhance the performance of VAWTs. The current study investigates the variations in loads and moments on the turbine as well as the experienced angle of attack, shed vorticity and boundary layer events (leading edge and trailing edge separation, laminar-to-turbulent transition) as a function of pitch angle using Computational Fluid Dynamics (CFD) calculations. Pitch angles of −7° to +3° are investigated using Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations while turbulence is modeled with the 4-equation transition SST model. The results show that a 6.6% increase in CP can be achieved using a pitch angle of −2° at a tip speed ratio of 4. Additionally, it is found that a change in pitch angle shifts instantaneous loads and moments between upwind and downwind halves of the turbine. The shift in instantaneous moment during the revolution for various pitch angles suggests that dynamic pitching might be a very promising approach for further performance optimization

New System for the Acceleration of the Airflow in Wind Turbines

Background: This patent is based on the wind industry technology called Diffuser Augmented Wind Turbines (DAWTs). This technology consists of a horizontal axis wind turbine, which is housed inside a duct with diverging section in the direction of the free air stream. In this paper, a review of preceding patents related to this technology is carried out. Objective: This paper presents an innovative patent to improve the performance of horizontal axis wind turbines. In particular, this system is aimed at improving the performance of those turbines that otherwise might not be installed due to the low wind resource existing at certain locations. Methods: The most innovative elements of this patent are: (1) the semi-spherical grooves, which are mechanized on the surface of the two diffusers in order to guarantee a more energetic boundary layer; (2) the coaxial diffuser, which is located downwind following the first diffuser in order to increase the suction effect on the air mass close to the inlet; (3) the coaxial rings located around the first diffuser outlet, which are used to deflect the external airflow toward the turbine wake; and (4), the selforientating system to orientate the system by the prevailing wind direction. Results: An application of the patent for increasing the power generated by a horizontal axis wind turbine with three blades is presented. The patent is designed and its performance is evaluated by using a Computational Fluid Dynamics code. The numerical results show that this system rises the airflow going through the rotor of the turbine. Conclusion: The patented device is an original contribution aimed at enabling a more profitable installation of wind turbines in places where the wind resource is insufficient because of the wind shear caused both by the proximity of the earth and the obstacles on the earth surface.This work was supported by the OASIS Research Project that was cofinanced by CDTI (Spanish Science and Innovation Ministry) and developed with the Spanish companies: Iridium, OHL Concesiones, Abertis, Sice, Indra, Dragados, OHL, Geocisa, GMV, Asfaltos Augusta, Hidrofersa, Eipsa, PyG, CPS, AEC and Torre de Comares Arquitectos S.L and 16 research centres. The authors also acknowledge the partial funding with FEDER funds under the Research Project FC-15-GRUPIN14-004. Finally, we also thank Swanson Analysis Inc. for the use of ANSYS University Research programs as well as the Workbench simulation environment

Towards smart blades for vertical axis wind turbines: different airfoil shapes and tip speed ratios

Future wind turbines will benefit from state-of-the-art technologies that allow them to not only operate efficiently in any environmental condition but also maximise the power output and cut the cost of energy production. Smart technology, based on morphing blades, is one of the promising tools that could make this possible. The present study serves as a first step towards designing morphing blades as functions of azimuthal angle and tip speed ratio for vertical axis wind turbines. The focus of this work is on individual and combined quasi-static analysis of three airfoil shape-defining parameters, namely the maximum thickness t/c and its chordwise position xt/c as well as the leading-edge radius index I. A total of 126 airfoils are generated for a single-blade H-type Darrieus turbine with a fixed blade and spoke connection point at c/2. The analysis is based on 630 high-fidelity transient 2D computational fluid dynamics (CFD) simulations previously validated with experiments. The results show that with increasing tip speed ratio the optimal maximum thickness decreases from 24 %c (percent of the airfoil chord length in metres) to 10 %c, its chordwise position shifts from 35 %c to 22.5 %c, while the corresponding leading-edge radius index remains at 4.5. The results show an average relative improvement of 0.46 and an average increase of nearly 0.06 in CP for all the values of tip speed ratio.</p

Effect of power on PPT discharge current

Purpose – The purpose of this paper is to investigate the effect of power on pulsed plasma thruster (PPT) discharge current with respect to its peak, duration, and behavior while the power elevates in a low power range. Design/methodology/approach – A rectangular parallel‐plate breech‐fed PPT has been developed with a self‐inductor coupling element connecting the PPT cathode to the ignitor plug cathode. The PPT has been operated in vacuum chamber at 10−6 mbar and its discharge current has been recorded using a Rogowski coil while input power has been changed by means of varying the capacitor voltage at given capacitance and frequency. Findings – The analysis leads to elucidate the effects of input power on discharge current of a PPT employing a self‐inductor coupling element. The power varies within a range of less than 10 to more than 50 W. The results show that current peak rises from 5 to 10 kA while discharge duration and behavior seems to be independent of power within the operating range. Additionally, utilization of the coupling element seems to change the typical oscillating behavior of PPT discharge to a more efficient behavior. Research limitations/implications – The analysis is mainly focused on breech‐fed PPTs while employing a coupling element. Originality/value – The paper analyzes the influence of power on discharge current of a PPT employing a self‐inductor coupling element. It clarifies the behavior of current peak, duration and behavior while power varies in a low power range. The effect of coupling element is shown to be promising. The results can be a help in design of μPPTs.Abdolrahim Rezaeih

Fuzzy attitude control system for a small satellite orbit maintenance using pulsed plasma thruster

This paper studies the application of pulsed plasma thrusters for autonomous station keeping of a remote sensing three-axis stabilized spacecraft flying at a low altitude due to inherent characteristics, while a fuzzy logic feedback law is employed for attitude control. Attitude stabilization is addressed using a reaction wheel and two magnetic torquers. The controller has been realized by means of a MIMO fuzzy controller with a knowledge base composed by 75 logic rules (25 logic rules for per axis). The Mamdani controllers use a standard max–min inference process and a fast center of area method to calculate the crisp control signals. Using hybrid actuators solve the singularity problem that often occurs in active magnetic control methods. The main features of the proposed control strategy are: simplicity in spacecraft control system design and development, increased robustness for automatic control reconfiguration and model uncertainty, reduction in development and production cost for flight control systems, autonomous on-board control features. Numerical simulation was carried out to testify the efficiency of the control system during station keeping. The satellite mass is approximately 60 kg, and has a bus power of approximately 100 W. The PPT's nominally aligned to the spacecraft velocity vector or x direction in body frame. The PPT is designed to produce near 0.9 mN of thrust at a specific impulse of 500 s using 25 W of power when its whole systems weighs less than 1.5 kg and is a breech-fed parallel-rail ablative PPT