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.

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.

Performance study of twisted Darrieus hydrokinetic turbine with novel blade design

2021 ◽  
pp. 1-37
Author(s):  
Mabrouk Mosbahi ◽  
Mouna Derbel ◽  
Mariem Lajnef ◽  
Bouzid Mosbahi ◽  
Zied Driss ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Small Scale ◽  
Performance Study ◽  
Hydrokinetic Turbine ◽  
Blade Shape ◽  
Water Turbine ◽  
Water Canals

Abstract Twisted Darrieus water turbine is receiving growing attentiveness for small-scale hydropower generation. Accordingly, the need for raised water energy conversion incentivizes researchers to focalise on the blade shape optimization of twisted Darrieus turbine. In view of this, an experimental analysis has been performed to appraise the efficiency of a spiral Darrieus water rotor in the present work. To better the performance parameters of the studied water rotor with twisted blades, three novel blade shapes, namely U-shaped blade, V-shaped blade and W-shaped blade, have been numerically tested using a computational fluid dynamics three-dimensional numerical model. Maximum power coefficient of Darrieus rotor reaches 0.17 at 0.63 tip-speed ratio using twisted blades. Using V-shaped blades, maximum power coefficient has been risen up to 0.185. The current study could be practically applied to provide more effective employment of twisted Darrieus turbines and to improve the generated power from flowing water such as river streams, tidal currents, or other man made water canals.

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.

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.

scholarly journals Comparative Numerical Analysis on Vertical Wind Turbine Rotor Pattern of Bach and Benesh Type

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2311 ◽  
Author(s):  
Fanel Dorel Scheaua
Keyword(s):  
Numerical Analysis ◽  
Classical Model ◽  
3D Models ◽  
Turbine Rotor ◽  
Point Of View ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Ansys Cfx ◽  
Torque Coefficient ◽  
Bladed Rotor

In this work, 3D models in classic configuration of Bach and Benesh rotor type, as well as models with modified blade pattern geometry were analyzed from the air circulation point of view inside the rotor enclosure in order to identify the operating parameters differences according to rotor geometric modified configuration. Constructive design aspects are presented, as well as results obtained from the virtual model analysis in terms of circulation velocity and pressure values which enhance rotor operation related to torque and power coefficients. The rotors design pattern is made according to previous results obtained by different researchers who have performed numerical analysis on virtual models and tests on the experimental rotor models using the wind tunnel. The constructive solutions are describing two-bladed rotor models, in four new designed constructive variants and analyzed using ANSYS CFX. The air velocity specific values, static and total pressure recorded at the rotor blade level are highlighted, that influence the obtaining of rotor shaft torque and power. Also torque coefficient (CT) and power coefficient (CP) values according with specific values of tip speed ratio (TSR) are presented for each analyzed case. The analysis results show higher power coefficient values for analyzed Bach V2 and Benesh V2 rotor modified models compared to the classic Bach and Benesh models for 0.3 TSR of 0.11–012 CP, 0.4 TSR of 0.18 CP (Benesh V2 model) and 0.27 CP at 0.6 TSR (Bach V2). The resulted values confirm that Benesh V2 model offers higher CP up to 5% at TSR 0.3, 2% at TSR 0.6 and 3% at TSR 0.4 compared to the Benesh classical model. The Bach V2 model offers 4% higher CP compared to the classic Bach model at TSR 0.6. Based on these results it is intended the further analytical and experimental research in order to obtain optimal rotor pattern.

scholarly journals On Blockage Effects for a Tidal Turbine in Free Surface Proximity

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3325 ◽  
Author(s):  
Nitin Kolekar ◽  
Ashwin Vinod ◽  
Arindam Banerjee
Keyword(s):  
Free Surface ◽  
Rotational Speed ◽  
Surface Deformation ◽  
Wake Flow ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Near Wake ◽  
Tidal Turbine ◽  
Free Surface Deformation ◽  
Surface Proximity

Experiments with a three-bladed, constant chord tidal turbine were undertaken to understand the influence of free surface proximity on blockage effects and near-wake flow field. The turbine was placed at various depths as rotational speeds were varied; thrust and torque data were acquired through a submerged sensor. Blockage effects were quantified in terms of changes in power coefficient and were found to be dependent on tip speed ratio and free surface to blade tip clearance. Flow acceleration near turbine rotation plane was attributed to blockage offered by the rotor, wake, and free surface deformation. In addition, particle image velocimetry was carried out in the turbine near-wake using time- and phase-averaged techniques to understand the mechanism responsible for the variation of power coefficient with rotational speed and free surface proximity. Slower wake propagation for higher rotational velocities and increased asymmetry in the wake with increasing free surface proximity was observed. Improved performance at high rotational speed was attributed to enhanced wake blockage, and performance enhancement with free surface proximity was due to the additional blockage effects caused by the free surface deformation. Proper orthogonal decomposition analysis revealed a downward moving wake for the turbine placed in near free surface proximity.

scholarly journals Numerical Investigation the Effect of the Different Tip Vanes on the Loading of an H-VAWT

2018 ◽  
Vol 53 ◽  
pp. 03041 ◽  
Author(s):  
Li Shoutu ◽  
Wang Yin ◽  
Yang Congxin ◽  
Li Ye
Keyword(s):  
Normal Force ◽  
Tangential Force ◽  
Three Dimensional ◽  
Fatigue Loading ◽  
Simulation Method ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Force Coefficient ◽  
Average Value ◽  
Unsteady Numerical Simulation

In this paper, the effect of the three typical tip vanes on the loading of an H-VAWT is investigated by employing the three-dimensional unsteady numerical simulation method. The results show that the both transient tangential force coefficient (CT) and normal force coefficient (Cn) have obvious change when the winglet and the V type vane is used at the blade's tip, respectively. However, in three tip vanes, the CT average value is the lowest and the CT fluctuation characteristic is the highest when the winglet is used. Although the winglet and V type vane contribute to change the transient CT and Cn, the normal force is increased too, it results in increasing fatigue loading and decreasing lifetime for H-VAWT. By comparison, the effect of the plate vane on the loading is weaker. Additionally, the winglet is advantage to improve power coefficient in the low tip speed ratio.

Numerical Analysis of Blockage Ratio Effect on a Portable Hydrokinetic Turbine

2016 ◽  
Author(s):  
Cosan Daskiran ◽  
Jacob Riglin ◽  
Alparslan Oztekin
Keyword(s):  
Free Stream ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Stream Velocity ◽  
Blockage Ratio ◽  
Ratio Effect ◽  
Turbine Performance ◽  
Hydrokinetic Turbine

Three-dimensional steady state Computational Fluid Dynamics (CFD) analyses were performed for a pre-designed micro-hydrokinetic turbine to investigate the blockage ratio effect on turbine performance. Simulations were conducted using a physical turbine rotor geometry rather than low fidelity, simplified actuator disk or actuator lines. The two-equation k-ω Shear Stress Transport (SST) turbulence model was employed to predict turbulence in the flow field. The turbine performance at the best efficiency point was studied for blockage ratios of 0.49, 0.70 and 0.98 for three different free stream velocities of 2.0 m/s, 2.25 m/s and 2.5 m/s. Distinct blockage ratio results at a free stream velocity of 2.25 were compared to a previous numerical study incorporating the same rotor geometry within an infinite flowing medium. The pressure gradient between turbine upstream and turbine downstream for blocked channel flows elevated the turbine performance. The increment in blockage ratio from 0.03 to 0.98 enhanced power coefficient from 0.437 to 2.254 and increased power generation from 0.56 kW to 2.86 kW for the present study.

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.

Study of horizontal axis tidal turbine performance and investigation on the optimum fixed pitch angle using CFD

2019 ◽  
Vol 30 (1) ◽  
pp. 206-227 ◽  
Author(s):  
Hoseyn A. Amiri ◽  
Rouzbeh Shafaghat ◽  
Rezvan Alamian ◽  
Seyed Mohamad Taheri ◽  
Mostafa Safdari Shadloo
Keyword(s):  
Pitch Angle ◽  
Flow Characteristics ◽  
Horizontal Axis ◽  
Speed Ratio ◽  
Wall Region ◽  
Computational Domain ◽  
Thrust Coefficient ◽  
Content Type ◽  
Tidal Turbine ◽  
Fixed Pitch

Purpose The purpose of this paper is to design, investigate and optimize a horizontal axis tidal turbine (HATT) using computer-aided numerical simulation and computational fluid dynamics (CFD). This is the first step of research and development (R&D) for implementation in the Persian Gulf condition. To do so, suitable locations are reviewed. Then, the optimization is focused on determining the optimum fixed pitch angle (β) of a three-bladed HATT based on the widespread multiple reference frame (MRF) technique to calculate power and thrust coefficients at different operational rotating speeds. Design/methodology/approach To simplify the problem and reducing the computational costs due to cyclic symmetry only one blade, accordingly one-third of the whole computational domain is considered in the modeling. Due to flow’s nature involving rotating, separation and recirculation, a realizable κ-ε turbulence model with standard wall function is selected to capture flow characteristics influenced by the rotor and near the wall region. Simulations are conducted for two free-stream velocities, then compared with their dependencies through the dimensionless tip speed ratio (TSR) parameter. Findings The validation process of the simulations is carried out by the use of AeroDyn BEM code, which has been evaluated by comparing with two experimental data. As results, the highest coefficient of power is achieved at ß = 19.3° at TSR = 4 with the value around 0.41 and 0.816 for thrust coefficient. Furthermore, to comprehend the rotor’s performance and simulation method, flow characteristics due to the rise in angular velocity is discussed in detail. Moreover, the major phenomenon, cavitation occurrence, is also checked at the critical situation where it is found to be safe. Originality/value By comparing and evaluating the results to other HATTs, it implies that the proposed rotor of this study is feasible and proved by CFD evaluation at this step. However, the current rotor is awaiting a justification through experimental assessment.

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