This research article discusses the active pitching technique for the H-Type Darrieus turbine and its importance for the turbine's self-starting and enhanced power coefficient. The pitch of the ...turbine blades is changed at various points while the turbine is whirling using the servomotor pitching control system. The performance of the turbine is enhanced by the present blade pitching method. The current analytical analysis made use of the DMST (Double Multiple Stream Tube) model. Parametric study is done to create a turbine design suitable for pre-fabrication. Currently, a turbine with a servomotor is being employed in the research. The paper's conclusion is that the current pitching schedule can increase initial torque to initiate starting of the turbine and improve efficiency of turbine in terms of power coefficient up to 45% for operating tip speed ratio, 0 = 2.5 at wind velocity of 10 m/s.
The Double Decker Turbine (DDT) is a recent design introduced for oscillating water column (OWC) devices. Its major contribution is the combination of two typical solutions in just one prototype: a ...self-rectifying performance, to deal with the bidirectional flow, and the twin-turbine concept, allowing the use of unidirectional turbines. This is achieved by a set of two concentric turbines, called external and internal turbines (ExT—InT). In this work, Computational Fluid Dynamics (CFD) numerical model is developed to study in detail the performance of a DDT, where geometrical components for both turbines have been taken from previous works of the authors. The ANSYS-Fluent code was first executed by means of a URANS simulation with a realizable k-ε turbulence model to obtain the performance curve of the turbine under steady conditions. Results obtained reveal its potential with respect to other solutions in the current state-of-the-art of OWC solutions for Wave Energy Conversion. Following a non-steady analysis, we assumed a sinusoidal input from the chamber which also resulted in promising results. Finally, the flow analysis inside the DDT allowed the authors to envisage geometric improvements that could enhance the DDT efficiency on future works.
The actual service life of wind turbine gearboxes is often well below the desired 20 years. One of the prevalent failure modes in gearbox bearing raceways is white structure flaking (WSF) by the ...formation of butterflies and white etching cracks with associated microstructural change called white etching areas. Despite these failures having been observed for two decades in various industries, the detailed reasons and mechanisms for their formation are not fully understood. In this review, white etching area formation mechanisms are discussed, specifically grain refinement, and effects of carbon/carbide in a range of bearing steels of widely differing carbon content. The review also highlights the severe transient, cyclic loading and tribochemical operating conditions of gearbox bearings and explains how these may act as drivers to produce WSF. Much previous research has focused on the detrimental effects of hydrogen, but other work suggests that hydrogen is not the only cause for WSF. Possible methods for preventing WSF are discussed, with attention paid to special steels such as high chromium steels, low carbon stainless nitrogen alloy steels and carbonitrided steels. Beneficial compressive residual stresses, surface coatings and enhanced lubrication and additive packages are shown to offer degrees of prevention, although the mechanisms leading to improvements are not fully understood.
•Dynamic stall of wind turbine airfoil with both VGs and LER is studied by URANS.•Increasing LER height further hinders the unsteady airfoil aerodynamic performance.•Serious LER may cause strong ...vortex shedding and change dynamic stall behaviors.•VGs can effectively control the dynamic stall and attenuate the adverse LER effect.•Double-row VGs generally perform better on roughened airfoils than single-row VGs.
Dynamic stall causes the highly unsteady and nonlinear aerodynamic loads on wind turbines. Recently, dynamic stall with passive vortex generators (VGs) and leading-edge roughness (LER) has received considerable attention, but independently. Therefore, this paper presents a careful investigation into dynamic stall of the NREL S809 airfoil with both VGs and LER to reveal their combined effect. Fully-resolved URANS simulations are conducted to identify the unsteady flow characteristics, and equivalent sand-grain roughness is used to model LER. LER significantly increases the turbulence kinetic energy (TKE) and suction loss at the leading edge, thereby causing the earlier onsets of separated flow and dynamic stall. Increasing roughness height generally reduces linear lift-curve slope, increases aerodynamic hysteresis and makes the separated flow hard to be reattached. VGs increase near-wall TKE via streamwise vortices and effectively suppress the separated flow. Dynamic stall is therefore significantly delayed by VGs with higher maximum lift, and aerodynamic hysteresis is also greatly reduced with the flow reattachment accelerated. Interestingly, serious LER may cause strong vortical disturbances and change the dynamic stall behaviors from light stall into deep stall. Double-row VGs are also found better than single-row VGs in improving the aerodynamic performance of roughened airfoil. These findings imply that VGs effectively control dynamic stall and diminish the adverse LER effect. This study should advance the control of unsteady loads on wind turbines suffering from harsh environmental conditions.
This paper presents an original approach to mitigate the motion of floating spar supports for offshore wind turbines. A two-degree-of-freedom tuned mass damper device, consisting of a chain of ...masses, linearly-elastic springs and viscous dashpots, is connected to the system within the nacelle. Considering a four-degree-of-freedom model of the system under simplified aerodynamic rotor loads, as well as Morison hydrodynamic loads, the proposed approach involves tuning the two natural frequencies of the device to the pitch natural frequency of the system and a relevant frequency within the range of the wave loads. Extensive numerical simulations on the OC3-Hywind spar floating wind turbine, for different load cases, prove that the proposed two-degree-of-freedom tuned mass damper is more effective than a standard single-degree-of-freedom one, assuming the two devices feature the same total mass. Further, design parameters are identified for representative loading conditions, in terms of ratio between the two masses within the device and ratio between the total masses of device and system.
•Mitigation of rigid-body oscillations in spar floating wind turbines.•Novel 2DOF TMD located in the nacelle of the wind turbine.•Numerical simulations on OC3-Hywind spar under turbulent wind and irregular waves.•Novel 2DOF TMD proves more efficient than 1DOF TMD with same mass.
•A novel approach of the turbine torque is proposed.•A unify model is capable of the dynamic characteristics of Pelton hydropower stations.•Sensitivity analysis from hydraulic parameters, mechanic ...parameters and electric parameters are performed.•Numerical simulations show the sensitivity ranges of the above three parameters.
Hydraulic turbine generator units with long-running operation may cause the values of hydraulic, mechanic or electric parameters changing gradually, which brings a new challenge, namely that whether the operating stability of these units will be changed in the next thirty or forty years. This paper is an attempt to seek a relatively unified model for sensitivity analysis from three aspects: hydraulic parameters (turbine flow and turbine head), mechanic parameters (axis coordinates and axial misalignment) and electric parameters (generator speed and excitation current). First, a novel approach of the Pelton turbine torque is proposed, which can make connections between the hydraulic turbine governing system and the shafting system of the hydro-turbine generator unit. Moreover, the correctness of this approach is verified by comparing with other three models of hydropower stations. Second, this latter is analyzed to obtain the sensitivity of electric parameter (excitation current), the mechanic parameters (axial misalignment, upper guide bearing rigidity, lower guide bearing rigidity, and turbine guide bearing rigidity) on hydraulic parameters on the operating stability of the unit. In addition to this, some critical values and ranges are proposed. Finally, these results can provide some bases for the design and stable operation of Peltonhydropower stations.
•A viscous damper system is proposed for wind turbine vibration control.•A simplified aerodynamic damping model is designed for finite element modeling.•The combination of surrogate and ...multi-objective optimization methods are adopted.
With the rapid development of the wind energy industry many wind farms have been constructed in regions prone to earthquakes and strong winds, which sometimes cause serious structural vibration problems for wind turbines. This paper details the development of a scissor-jack braced viscous damper system (VD-SJB) to suppress excessive vibration of the wind turbine tower. This system can be installed inside the tubular steel tower and is a suitable technology to enhance the structural performance of existing wind turbines. A detailed finite element wind turbine model was built and two damper systems with and without SJB were modelled and compared. Ground motions and strong lateral winds were applied as external loads to operational and parked turbines, respectively. Parameter optimization was performed by building a surrogate model using an artificial neural network and a multi-objective genetic algorithm. The resulting Pareto sets were discussed and the optimal system was evaluated to demonstrate the effectiveness of VD-SJB. Results show that both viscous dampers installed vertically and VD-SJB are able to reduce structural vibrations under seismic or wind conditions. However, VD-SJB is capable of magnifying the stroke of the damper and decrease the damping force, thus it is a more practical solution.
The work presents a dynamic simulation and an energy and economic analysis of two different Building Integrated Solar Technologies, namely: Building Integrated PhotoVoltaic (BIPV) collectors and ...Building Integrated hybrid PhotoVoltaic-Thermal (BIPVT) collectors. Both systems are coupled with small size Wind Turbines (WTs), to reduce the fluctuations of power production typical of solar systems. A case study is presented, referred to a hotel building, where a reversible air-to-water Heat Pump (HP) is used for space heating and cooling, driven by the electric energy provided by PV collectors and WTs. In order to optimize the HP performance in cooling mode, thermal energy is recovered from the HP desuperheater and used to produce domestic hot water (DHW). A two-stage cascade cycle HP for DHW purposes was also investigated, as a further alternative. The systems were simulated by means of a dynamic simulation model, developed in TRNSYS. The results show that the BIPV-based system is more profitable than the BIPVT one, achieving a simple payback period of about 4.5 years; for both systems, the optimum size of the WT system, for a given area of PV collectors, was also investigated.
•Building integrated photovoltaic and photovoltaic/thermal collectors are compared.•Combination of solar and wind energy to reduce fluctuations of power production.•Systems are dynamically simulated in TRNSYS environment.•Simple payback period of about 4.5 years for photovoltaic-based system.
In this study, the effect of inlet air cooling on greenhouse gas (GHG) emissions and engine performance for a land-based gas turbine engine was investigated under varying ambient temperatures (15–55 ...°C). The study aimed to reduce GHG emissions while improving output power and fuel efficiency during hot weather operating conditions. For illustrative purposes, a representative gas turbine engine model, approximating the 250 MW class General Electric (GE) engine, was analyzed in a simple cycle. A refrigeration process was integrated with a turboshaft gas turbine engine to chill the incoming air, and the power required for cooling was extracted from the gas turbine’s output power. This mechanical chiller was assumed to provide a 15 °C inlet air temperature. Without inlet air cooling, at 55 °C ambient temperature, the engine’s power output was calculated to decrease by 15.06%, while power-specific fuel consumption and GHG emissions increased by 6.09% and 5.84%, respectively. However, activating the refrigeration or cooling system in the inlet made it possible to mitigate most of the adverse effects of hot weather on the engine’s performance and GHG emissions. Therefore, with inlet air cooling, the power output loss reduces to 3.28%, indicating an 11.78% recovery compared to the 15.06% loss without cooling. Similarly, the rise in power-specific fuel consumption caused by high ambient temperature decreases from 6.09% to 3.43%, reflecting a 2.66% improvement. An important finding of the study is that with inlet air cooling, the increase in GHG emissions reduces from 5.84% to 3.41%, signifying a 2.43% improvement on a hot day with a temperature of 55 °C.
Operators of wind power facilities can mitigate wildlife mortality by slowing or stopping wind turbines (hereafter ‘curtail’) when birds are at an increased risk of collision. Some facility operators ...curtail when individual birds have flight characteristics (e.g. altitude, distance or relative bearing of a bird's flight path) that exceed some threshold value, but thresholds currently in use have not been empirically evaluated. Overly restrictive thresholds can cause turbine curtailment for birds that never enter rotor‐swept zones, thereby resulting in excess power loss. We evaluated the probability that birds, specifically eagles, entered the rotor‐swept zone (hereafter ‘entry probability’) in response to their flight characteristics. We used an automated monitoring system to classify individuals as eagles or non‐eagles and record flight paths of purported eagles at a wind facility in Wyoming, USA. We used logistic regression with occupancy dynamics and a distance‐dependent colonization process to model entry probability. As a result, this model allowed entry probability to decrease with horizontal distance to the nearest turbine. The probability of entry varied with distance to the nearest turbine and approached zero when that distance was more than 202 m. Entry probability peaked when eagles flew 89 m above ground, corresponding to hub heights of turbines (80 m), and decreased to near‐zero at altitudes of 189 m or more. Entry probabilities were greatest when flight paths were near the rotor‐swept zone and when eagles flew slowly toward the nearest turbine. Compass bearing of a flight path was not associated with entry probability. Our model accurately forecasted entry probability in Wyoming (area under the curve (AUC) = 0.96) and was transferable to another facility in California, USA (AUC = 0.97); therefore, our results may be applicable across a variety of settings. Curtailment criteria can be based on flight path characteristics to forecast entry into rotor‐swept zones. The use of distance and altitude thresholds when making curtailment decisions is justified. However, this analysis suggests alteration of the time to collision threshold, with curtailment initiated at greater distances as the speed of the bird decreases. Our novel modelling method and our results can inform curtailment criteria in any situation where curtailment decisions are made in real‐time.
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