scholarly journals Aerodynamic Analysis of a Wind-Turbine Rotor Affected by Pitch Unbalance

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 745
Author(s):  
Francesco Castellani ◽  
Abdelgalil Eltayesh ◽  
Matteo Becchetti ◽  
Antonio Segalini
Keyword(s):  
Applied Load ◽  
Detrimental Effect ◽  
Turbine Rotor ◽  
The Other ◽  
Power Coefficient ◽  
Mean Velocity ◽  
Thrust Coefficient ◽  
Tip Vortices ◽  
The Mean ◽  
Wind Turbine Rotor

The aerodynamics of a rotor with pitch imbalance has been investigated experimentally and numerically in the present work. The comparison of mean velocity and turbulence intensity in the balanced and unbalanced cases indicated that a pitch imbalance modifies both the mean velocity and the turbulent activity; the latter is weakly increased by the imbalance. Spectral analysis indicated that the dynamics of the wake is also affected by the pitch imbalance since the tip vortices loose strength and disorganise more quickly than in the balanced case. The pitch imbalance has, however, a detrimental effect on the power coefficient and it affects the thrust coefficient as well. Only the blade affected by the imbalance shows significant modifications of the applied load, while the other blades operate with the same loading conditions.

scholarly journals Performance and wake characteristics of a tidal turbine under yaw

2018 ◽  
Vol 1 (1 (Aug)) ◽  
pp. 41-50 ◽  
Author(s):  
P. Modali ◽  
N. S. Kolekar ◽  
A. Banerjee
Keyword(s):  
Center Of Mass ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Thrust Coefficient ◽  
Tip Vortices ◽  
Downstream Distance ◽  
Tidal Turbine ◽  
Yaw Angle

In tidal streams and rivers, the flow of water can be at yaw to the turbine rotor plane causing performance degradation and a skewed downstream wake. The current study aims to quantify the performance variation and associated wake behavior caused by a tidal turbine operating in a yawed inflow environment. A three-dimensional computational fluid dynamics study was carried out using multiple reference frame approach using κ-ω SST turbulence model with curvature correction. The computations were validated by comparison with experimental results on a 1:20 scale prototype for a 0° yaw case performed in a laboratory flume. The simulations were performed using a three-bladed, constant chord, untwisted tidal turbine operating at uniform inflow. Yaw effects were observed for angles ranging from 5° to 15°. An increase in yaw over this range caused a power coefficient deficit of 26% and a thrust coefficient deficit of about 8% at a tip speed ratio of 5 that corresponds to the maximum power coefficient for the tested turbine. In addition, wake propagation was studied up to a downstream distance of ten rotor radius, and skewness in the wake, proportional to yaw angle was observed. At higher yaw angles, the flow around the turbine rotor was found to cushion the tip vortices, accelerating the interaction between the tip vortices and the skewed wake, thereby facilitating a faster wake recovery. The center of the wake was tracked using a center of mass technique. The center of wake analysis was used to better quantify the deviation of the wake with increasing yaw angle. It was observed that with an increase in yaw angle, the recovery distance moved closer to the rotor plane. The wake was noticed to meander around the turbine centerline with increasing downstream distance and slightly deviate towards the free surface above the turbine centerline, magnitude of which varied depending on yaw.

Development of a Scaled Rotor Blade for Tank Tests of Floating Wind Turbine Systems

2018 ◽  
Author(s):  
Paul Schünemann ◽  
Timo Zwisele ◽  
Frank Adam ◽  
Uwe Ritschel
Keyword(s):  
Wind Turbine ◽  
Rotor Blade ◽  
Turbine Rotor ◽  
Full Scale ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Model Scale ◽  
Floating Wind Turbine ◽  
Hydrodynamic Effects ◽  
Wind Turbine Rotor

Floating wind turbine systems will play an important role for a sustainable energy supply in the future. The dynamic behavior of such systems is governed by strong couplings of aerodynamic, structural mechanic and hydrodynamic effects. To examine these effects scaled tank tests are an inevitable part of the design process of floating wind turbine systems. Normally Froude scaling is used in tank tests. However, using Froude scaling also for the wind turbine rotor will lead to wrong aerodynamic loads compared to the full-scale turbine. Therefore the paper provides a detailed description of designing a modified scaled rotor blade mitigating this problem. Thereby a focus is set on preserving the tip speed ratio of the full scale turbine, keeping the thrust force behavior of the full scale rotor also in model scale and additionally maintaining the power coefficient between full scale and model scale. This is achieved by completely redesigning the original blade using a different airfoil. All steps of this redesign process are explained using the example of the generic DOWEC 6MW wind turbine. Calculations of aerodynamic coefficients are done with the software tools XFoil and AirfoilPrep and the resulting thrust and power coefficients are obtained by running several simulations with the software AeroDyn.

On Turbulent Flow Between Parallel Plates

1953 ◽  
Vol 20 (1) ◽  
pp. 109-114
Author(s):  
S. I. Pai
Keyword(s):  
Turbulent Flow ◽  
Velocity Distribution ◽  
Poiseuille Flow ◽  
The Other ◽  
Turbulent Velocity ◽  
Parallel Plates ◽  
Mean Velocity ◽  
Reynolds Equations ◽  
Mean Pressure ◽  
The Mean

Abstract The Reynolds equations of motion of turbulent flow of incompressible fluid have been studied for turbulent flow between parallel plates. The number of these equations is finally reduced to two. One of these consists of mean velocity and correlation between transverse and longitudinal turbulent-velocity fluctuations u 1 ′ u 2 ′ ¯ only. The other consists of the mean pressure and transverse turbulent-velocity intensity. Some conclusions about the mean pressure distribution and turbulent fluctuations are drawn. These equations are applied to two special cases: One is Poiseuille flow in which both plates are at rest and the other is Couette flow in which one plate is at rest and the other is moving with constant velocity. The mean velocity distribution and the correlation u 1 ′ u 2 ′ ¯ can be expressed in a form of polynomial of the co-ordinate in the direction perpendicular to the plates, with the ratio of shearing stress on the plate to that of the corresponding laminar flow of the same maximum velocity as a parameter. These expressions hold true all the way across the plates, i.e., both the turbulent region and viscous layer including the laminar sublayer. These expressions for Poiseuille flow have been checked with experimental data of Laufer fairly well. It also shows that the logarithmic mean velocity distribution is not a rigorous solution of Reynolds equations.

Four Decades of Research Into the Augmentation Techniques of Savonius Wind Turbine Rotor

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Nur Alom ◽  
Ujjwal K. Saha
Keyword(s):  
Wind Turbine ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Major Drawback ◽  
High Rotational Speed ◽  
Savonius Rotor ◽  
Augmentation Techniques ◽  
Savonius Wind Turbine ◽  
Low Efficiency ◽  
Wind Turbine Rotor

The design and development of wind turbines is increasing throughout the world to offer electricity without paying much to the global warming. The Savonius wind turbine rotor, or simply the Savonius rotor, is a drag-based device that has a relatively low efficiency. A high negative torque produced by the returning blade is a major drawback of this rotor. Despite having a low efficiency, its design simplicity, low cost, easy installation, good starting ability, relatively low operating speed, and independency to wind direction are its main rewards. With the goal of improving its power coefficient (CP), a considerable amount of investigation has been reported in the past few decades, where various design modifications are made by altering the influencing parameters. Concurrently, various augmentation techniques have also been used to improve the rotor performance. Such augmenters reduce the negative torque and improve the self-starting capability while maintaining a high rotational speed of the rotor. The CP of the conventional Savonius rotors lie in the range of 0.12–0.18, however, with the use of augmenters, it can reach up to 0.52 with added design complexity. This paper attempts to give an overview of the various augmentation techniques used in Savonius rotor over the last four decades. Some of the key findings with the use of these techniques have been addressed and makes an attempt to highlight the future direction of research.

Experimental Study on Near-Wall Bubble Clustering Behaviors in Bubbly Channel Flow (Keynote)

2003 ◽  
Author(s):  
Soo-Hyun So ◽  
Shu Takagi ◽  
Akiko Fujiwara ◽  
Yoichiro Matsumoto
Keyword(s):  
Liquid Phase ◽  
Bubble Size ◽  
The Other ◽  
Image Processing Technique ◽  
Cluster Center ◽  
Turbulence Structure ◽  
Mean Velocity ◽  
Bubble Cluster ◽  
The Mean ◽  
Near Wall

The turbulence properties of gas-liquid bubbly flows and the near-wall bubble clustering behaviors are investigated for upward flow in a rectangular channel. Bubble size distributions are well-controlled and the flow with mono-dispersed 1mm-diameter and that with 1–4mm diameter bubbles are compared. Bubble size, turbulent properties of liquid phase and the bubble cluster motion were measured using image-processing technique, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV), respectively. To create the mono-dispersed small bubbles by the bubble generator, being made of stainless steel pipes, a small amount of surfactant (20ppm of 3-pentanol) was added into the flow. In this study, experiments with three different bulk Reynolds numbers (1350, 4100, 8200) were conducted with void fractions less than 0.6% in the fluid with/without the surfactant. In all cases with surfactant, there was a very high accumulation of bubbles near the wall. The local void fraction has a wall-peak distribution and the horizontal bubble clusters are formed near the wall. As a result, the local mean velocity of the liquid phase becomes larger near the wall due to the driving force of buoyant bubbles and the stream-wise turbulent intensity in the vicinity of the wall was enhanced. On the other hand, the turbulent fluctuations and Reynolds stress are remarkably suppressed in the other region. At the Reynolds number of 8200, the bubble cluster was investigated. Experimental observation showed that the bubble cluster changes its shape in time and that the shape change is caused by the difference of the rising velocity between the cluster center and the both ends. The clusters accelerated the mean streamwise velocity near the wall, thus the mean velocity profile of the liquid phase becomes flattened. It is suggested that the highly concentrated bubbles in the vicinity of the wall disturb the transport of turbulence energy produced in the wall shear layer toward the center of channel. Moreover, in the middle of channel, the turbulence structure is governed by pseudo-turbulence induced by present bubbles.

Existence of a sharp transition in the peak propulsive efficiency of a low- pitching foil

2016 ◽  
Vol 800 ◽  
pp. 307-326 ◽  
Author(s):  
Anil Das ◽  
Ratnesh K. Shukla ◽  
Raghuraman N. Govardhan
Keyword(s):  
Power Coefficient ◽  
Energetic Cost ◽  
Mean Power ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Von Karman ◽  
Wide Range ◽  
The Mean ◽  
The One ◽  
Von Kármán

We perform a comprehensive characterization of the propulsive performance of a thrust generating pitching foil over a wide range of Reynolds ($10\leqslant Re\leqslant 2000$) and Strouhal ($St$) numbers using a high-resolution viscous vortex particle method. For a given $Re$, we show that the mean thrust coefficient $\overline{C_{T}}$ increases monotonically with $St$, exhibiting a sharp rise as the location of the inception of the wake asymmetry shifts towards the trailing edge. As a result, the propulsive efficiency too rises steeply before attaining a maximum and eventually declining at an asymptotic rate that is consistent with the inertial scalings of $St^{2}$ for $\overline{C_{T}}$ and $St^{3}$ for the mean power coefficient, with the latter scaling holding, quite remarkably, over the entire range of $Re$. We find the existence of a sharp increase in the peak propulsive efficiency ${\it\eta}_{max}$ (at a given $Re$) in the $Re$ range of 50 to approximately 1000, with ${\it\eta}_{max}$ increasing rapidly from about 1.7 % to the saturated asymptotic value of approximately $16\,\%$. The $St$ at which ${\it\eta}_{max}$ is attained decreases progressively with $Re$ towards an asymptotic limit of $0.45$ and always exceeds the one for transition from a reverse von Kármán to a deflected wake. Moreover, the drag-to-thrust transition occurs at a Strouhal number $St_{tr}$ that exceeds the one for von Kármán to reverse von Kármán transition. The $St_{tr}$ and the corresponding power coefficient $\overline{C_{p,}}_{tr}$ are found to be remarkably consistent with the simple scaling relationships $St_{tr}\sim Re^{-0.37}$ and $\overline{C_{p,}}_{tr}\sim Re^{-1.12}$ that are derived from a balance of the thrust generated from the pitching motion and the drag force arising out of viscous resistance to the foil motion. The fact that the peak propulsive efficiency degrades appreciably only below $Re\approx 10^{3}$ establishes a sharp lower threshold for energetically efficient thrust generation from a pitching foil. Our findings should be generalizable to other thrust-producing flapping foil configurations and should aid in establishing the link between wake patterns and energetic cost of thrust production in similar systems.

scholarly journals A method for preliminary rotor design – Part 1: Radially Independent Actuator Disc model

2021 ◽  
Vol 6 (3) ◽  
pp. 903-915 ◽  
Author(s):  
Kenneth Loenbaek ◽  
Christian Bak ◽  
Jens I. Madsen ◽  
Michael McWilliam
Keyword(s):  
Power Optimization ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Analytical Relationship ◽  
Local Power ◽  
Step Method ◽  
Thrust Coefficient ◽  
Rotor Design ◽  
Viscous Loss ◽  
Actuator Disc

Abstract. We present an analytical model for assessing the aerodynamic performance of a wind turbine rotor through a different parametrization of the classical blade element momentum (BEM) model. The model is named the Radially Independent Actuator Disc (RIAD) model, and it establishes an analytical relationship between the local thrust loading and the local power, known as the local-thrust coefficient and the local-power coefficient respectively. The model has a direct physical interpretation, showing the contribution for each of the three losses: wake rotation loss, tip loss and viscous loss. The gradient for RIAD is found through the use of the complex step method, and power optimization is used to show how easily the method can be used for rotor optimization. The main benefit of RIAD is the ease with which it can be applied for rotor optimization and especially load constraint power optimization as described in Loenbaek et al. (2021). The relationship between the RIAD input and the rotor chord and twist is established, and it is validated against a BEM solver.

Strategic Blade Shape Optimization for Aerodynamic Performance Improvement of Wind Turbines

2016 ◽  
Author(s):  
Youjin Kim ◽  
Ali Al-Abadi ◽  
Antonio Delgado
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Optimization Methods ◽  
Turbine Rotor ◽  
Aerodynamic Performance ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Blade Shape ◽  
Improved Design ◽  
Wind Turbine Rotor

This study introduces strategic methods for improving the aerodynamic performance of wind turbines. It was completed by combining different optimization methods for each part of the wind turbine rotor. The chord length and pitch angle are optimized by a torque-matched method (TMASO), whereas the airfoil shape is optimized by the genetic algorithm (GA). The TMASO is implemented to produce an improved design of a reference turbine (NREL UAE Phase V). The GA is operated to generate a novel airfoil design that is evaluated by automatic interfacing for the highest gliding ratio (GR). The adopted method produces an optimized wind turbine with an 11% increase of power coefficient (Cp) with 30% less of the corresponding tip speed ratio (TSR). Furthermore, the optimized wind turbine shows reduced tip loss effect.

scholarly journals Optimum Power Output Control of a Wind Turbine Rotor

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
S. Wijewardana ◽  
M. H. Shaheed ◽  
R. Vepa
Keyword(s):  
Equilibrium Point ◽  
Wind Turbine ◽  
Power Output ◽  
Turbine Blades ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Output Control ◽  
The Stability ◽  
Lift And Drag ◽  
Wind Turbine Rotor

An active and optimum controller is applied to regulate the power output from a wind turbine rotor. The controller is synthesized in two steps. The first step defines the equilibrium operation point and ensures that the desired equilibrium point is stable. The stability of the equilibrium point is guaranteed by a control law that is synthesized by applying the methodology of model predictive control (MPC). The method of controlling the turbine involves pitching the turbine blades. In the second step the blade pitch angle demand is defined. This involves minimizing the mean square error between the actual and desired power coefficient. The actual power coefficient of the wind turbine rotor is evaluated assuming that the blade is capable of stalling, using blade element momentum theory. This ensures that the power output of the rotor can be reduced to any desired value which is generally not possible unless a nonlinear stall model is introduced to evaluate the blade profile coefficients of lift and drag. The relatively simple and systematic nonlinear modelling and MPC controller synthesis approach adopted in this paper clearly highlights the main features on the controller that is capable of regulating the power output of the wind turbine rotor.

scholarly journals Offshore Transport of Dense Water from the East Greenland Shelf

2014 ◽  
Vol 44 (1) ◽  
pp. 229-245 ◽  
Author(s):  
B. E. Harden ◽  
R. S. Pickart ◽  
I. A. Renfrew
Keyword(s):  
Wind Forcing ◽  
The Other ◽  
Mean Velocity ◽  
East Greenland ◽  
Dense Water ◽  
Denmark Strait ◽  
The Mean ◽  
Coastally Trapped Waves ◽  
Offshore Transport ◽  
Shelf Flow

Abstract Data from a mooring deployed at the edge of the East Greenland shelf south of Denmark Strait from September 2007 to October 2008 are analyzed to investigate the processes by which dense water is transferred off the shelf. It is found that water denser than 27.7 kg m−3—as dense as water previously attributed to the adjacent East Greenland Spill Jet—resides near the bottom of the shelf for most of the year with no discernible seasonality. The mean velocity in the central part of the water column is directed along the isobaths, while the deep flow is bottom intensified and veers offshore. Two mechanisms for driving dense spilling events are investigated, one due to offshore forcing and the other associated with wind forcing. Denmark Strait cyclones propagating southward along the continental slope are shown to drive off-shelf flow at their leading edges and are responsible for much of the triggering of individual spilling events. Northerly barrier winds also force spilling. Local winds generate an Ekman downwelling cell. Nonlocal winds also excite spilling, which is hypothesized to be the result of southward-propagating coastally trapped waves, although definitive confirmation is still required. The combined effect of the eddies and barrier winds results in the strongest spilling events, while in the absence of winds a train of eddies causes enhanced spilling.

Sign in / Sign up

Export Citation Format

Share Document