Numerical simulation and experimental study of blade pitch effect on Darrieus straight-bladed wind turbine with high solidity

Increasing the solidity in vertical axis wind turbines (VAWT) leads to the decreased coefficient of performance (COP) despite the improved start-up performance. To overcome this problem, the pitch regulation system is proposed in this paper for increasing the solidity. In most of the previous investigations, the effect of pitch angle was tested on low-solidity VAWT at uniform flow conditions and low turbulence intensity in wind tunnel test sections, which are different from the real conditions. In this investigation, the influence of pitch angle on the aerodynamic performance of a small Darrieus-type straight-bladed high-solidity VAWT equipped with a pitch regulation system is investigated numerically and experimentally under realistic condition. The proposed numerical procedure is validated through experimental test results. The COP is measured and calculated at different tip speed ratios and two pitch angles of 0 and 5°. The results reveal 25% enhancement in maximum COP with the increase of pitch angle up to 5°. Moreover, according to the numerical results, higher accuracy can be obtained at lower tip speed ratios for both pitch angles. Then, the numerical method is employed to calculate the power (performance) and torque coefficients as a function of Azimuth position as well as the flow field in rotor affected zone and lateral distance. It is found that increasing the pitch angle at a constant tip speed ratio is followed by accelerated vorticity generation, occurrence of maximum COP at lower tip speed ratio and smoother velocity profile in lateral distances of the rotor.

Effect of Pitch Parameters on Aerodynamic Forces of a Straight-Bladed Vertical Axis Wind Turbine with Inclined Pitch Axes

Pitch regulation plays a significant role in improving power performance and achieving output control in wind turbines. The present study focuses on a novel, pitch-regulated vertical axis wind turbine (VAWT) with inclined pitch axes. The effect of two pitch parameters (the fold angle and the incline angle) on the instantaneous aerodynamic forces and overall performance of a straight-bladed VAWT under a tip-speed ratio of 4 is investigated using an actuator line model, achieved in ANSYS Fluent software and validated by previous experimental results. The results demonstrate that the fold angle has an apparent influence on the angles of attack and forces of the blades, as well as the power output of the wind turbine. It is helpful to further study the dynamic pitch regulation and adaptable passive pitch regulation of VAWTs. Incline angles away from 90° lead to the asymmetric distribution of aerodynamic forces along the blade span, which results in an expected reduction of loads on the main shaft and the tower of VAWTs.

Highly intrinsic thermal conductivity of cellulose nanocrystals films through pitch regulation

Polymers are widely used in modern electronics thermal management systems, due to their light weight, electrical insulation, and low cost. However, the low intrinsic thermal conductivity (TC) of polymer restricts...

Design of Rigid Body Dynamics for Pitch Regulation Mechanism to Maximize Energy Capture by Wind Turbine

Wind turbines are generally designed for specific wind speeds and at below or above these speeds wind turbine could not give the expected maximum power. To obtain the maximum power at different wind speeds, pitching mechanism of the blades introduced. Mostly active pitching is used on large scale but the study gives detail advantages, design and analysis of passive pitching which is free of electronics. The study suggested the design that through centrifugal masses the rotor is able to changes the pitch angles through 10 degrees which are enough for wind speed ranges from 4-20 m/s which maintain the optimum angle of attack maximizing the power output. This report includes an in- depth analysis of design process, detailed components and assembly, recommendations, and conclusions.

Effector-independent brain network for auditory-motor integration: fMRI evidence from singing and cello playing

Many everyday tasks share high-level sensory goals but differ in the movements used to accomplish them. One example of this is musical pitch regulation, where the same notes can be produced using the vocal system or a musical instrument controlled by the hands. Cello playing has previously been shown to rely on brain structures within the singing network for performance of single notes, except in areas related to primary motor control, suggesting that the brain networks for auditory feedback processing and sensorimotor integration may be shared (Segado et al. 2018). However, research has shown that singers and cellists alike can continue singing/playing in tune even in the absence of auditory feedback (Chen et al. 2013, Kleber et al. 2013), so different paradigms are required to test feedback monitoring and control mechanisms. In singing, auditory pitch feedback perturbation paradigms have been used to show that singers engage a network of brain regions including anterior cingulate cortex (ACC), anterior insula (aINS), and intraparietal sulcus (IPS) when compensating for incorrect pitch feedback, and posterior superior temporal gyrus (pSTG) and supramarginal gyrus (SMG) when ignoring it (Zarate et al. 2005, 2008). To determine whether the brain networks for cello playing and singing directly overlap in these sensory-motor integration areas, in the present study expert cellists were asked to compensate for or ignore introduced pitch perturbations when singing/playing during fMRI scanning. We found that cellists were able to sing/play target tones, and compensate for and ignore introduced feedback perturbations equally well. Brain activity overlapped for singing and playing in IPS and SMG when compensating, and pSTG and dPMC when ignoring; differences between singing/playing across all three conditions were most prominent in M1, centered on the relevant motor effectors (hand, larynx). These findings support the hypothesis that pitch regulation during cello playing relies on structures within the singing network and suggests that differences arise primarily at the level of forward motor control.HighlightsExpert cellists were asked to compensate for or ignore introduced pitch perturbations when singing/playing during fMRI scanning.Cellists were able to sing/play target tones, and compensate for and ignore introduced feedback perturbations equally well.Brain activity overlapped for singing and playing in IPS and SMG when compensating, and pSTG and dPMC when ignoring.Differences between singing/playing across were most prominent in M1, centered around the relevant motor effectors (hand, larynx)Findings support the hypothesis that pitch regulation during cello playing relies on structures within the singing network with differences arising primarily at the level of forward motor control

Top–Down Inhibitory Mechanisms Underlying Auditory–Motor Integration for Voice Control: Evidence by TMS

The dorsolateral prefrontal cortex (DLPFC) has been implicated in auditory–motor integration for accurate control of vocal production, but its precise role in this feedback-based process remains largely unknown. To this end, the present event-related potential study applied a transcranial magnetic stimulation (TMS) protocol, continuous theta-burst stimulation (c-TBS), to disrupt cortical activity in the left DLPFC as young adults vocalized vowel sounds while hearing their voice unexpectedly shifted upwards in pitch. The results showed that, as compared to the sham condition, c-TBS over left DLPFC led to significantly larger vocal compensations for pitch perturbations that were accompanied by significantly smaller cortical P2 responses. Source localization analyses revealed that this brain activity pattern was the result of reduced activation in the left superior frontal gyrus and right inferior parietal lobule (supramarginal gyrus). These findings demonstrate c-TBS-induced modulatory effects of DLPFC on the neurobehavioral processing of vocal pitch regulation, suggesting that disrupting prefrontal function may impair top–down inhibitory control mechanisms that prevent speech production from being excessively influenced by auditory feedback, resulting in enhanced vocal compensations for feedback perturbations. This is the first study that provides direct evidence for a causal role of the left DLPFC in auditory feedback control of vocal production.

Scaling of the performance of insect-inspired passive-pitching flapping wings

Flapping flight using passive pitch regulation is a commonly used mode of thrust and lift generation in insects and has been widely emulated in flying vehicles because it allows for simple implementation of the complex kinematics associated with flapping wing systems. Although robotic flight employing passive pitching to regulate angle of attack has been previously demonstrated, there does not exist a comprehensive understanding of the effectiveness of this mode of aerodynamic force generation, nor a method to accurately predict its performance over a range of relevant scales. Here, we present such scaling laws, incorporating aerodynamic, inertial and structural elements of the flapping-wing system, validating the theoretical considerations using a mechanical model which is tested for a linear elastic hinge and near-sinusoidal stroke kinematics over a range of scales, hinge stiffnesses and flapping frequencies. We find that suitably defined dimensionless parameters, including the Reynolds number, Re , the Cauchy number, Ch , and a newly defined ‘inertial-elastic’ number, IE, can reliably predict the kinematic and aerodynamic performance of the system. Our results also reveal a consistent dependency of pitching kinematics on these dimensionless parameters, providing a connection between lift coefficient and kinematic features such as angle of attack and wing rotation.

Comparative Fatigue Life Assessment of Wind Turbine Blades Operating with Different Regulation Schemes

A comparative evaluation of the fatigue damage occurring in the blades of small wind turbines, with different power regulation schemes, has been conducted for the first time. Three representative test cases were built, one based on stall regulation and two using pitch regulation. The power curves were tuned to be identical in all cases, in order to allow for a direct comparison of fatigue damage. A methodology combining a dynamic simulation of a wind turbine forced by stochastic wind speed time series, with the application of the IEC 61400-2 standard, was designed and applied for two levels of turbulence intensity. The effect of the wind regime was studied by considering Weibull-distributed wind speeds with a variety of parameter sets. Not unexpectedly, in typical wind regimes, stall regulation led to a generally higher fatigue damage than pitch regulation, for similar structural blade design, but the practical implications were smaller than thought previously. Given the need for cost-effective designs for small wind turbines, stall regulation may be a viable alternative for off-grid applications.