scholarly journals Parametric Study on a Performance of a Small Counter-Rotating Wind Turbine

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3880
Author(s):  
Michał Pacholczyk ◽  
Dariusz Karkosiński
Keyword(s):  
Wind Turbine ◽  
Parametric Study ◽  
Rotor Blades ◽  
Speed Ratio ◽  
Outer Diameter ◽  
Axial Distance ◽  
Computational Domain ◽  
Dynamic Interactions ◽  
Computational Fluids Dynamics ◽  
Large Eddy

A small Counter-Rotating Wind Turbine (CRWT) has been proposed and its performance has been investigated numerically. Results of a parametric study have been presented in this paper. As parameters, the axial distance between rotors and a tip speed ratio of each rotor have been selected. Performance parameters have been compared with reference to a Single Rotor Wind Turbine (SRWT). Simulations were carried out with Computational Fluids Dynamics (CFD) solver and a Large Eddy Scale approach to model turbulences. An Actuator Line Model has been chosen to represent rotors in the computational domain. Summing up the results of simulation tests, it can be stated that when constructing a CRWT turbine, rotors should be placed at a distance of at least 0.5 D (where D is rotor outer diameter) or more. One can then expect a noticeable power increase compared to a single rotor turbine. Placing the second rotor closer than 0.5 D guarantees a significant increase in power, but in such configurations, dynamic interactions between the rotors are visible, resulting in fluctuations in torque and power. Dynamic interactions between rotor blades above 0.5 D are invisible.

Aerodynamic Design and Analysis of a Flanged Diffuser Augmented Wind Turbine

2013 ◽  
Author(s):  
A. Tourlidakis ◽  
K. Vafiadis ◽  
V. Andrianopoulos ◽  
I. Kalogeropoulos
Keyword(s):  
Wind Speed ◽  
Flow Field ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Research Work ◽  
Flow Analysis ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Computational Domain ◽  
Aerodynamic Design

Many researchers proposed methods for improving the efficiency of small Horizontal Axis Wind Turbines (HAWTs). One of the methods developed to increase the efficiency of HAWTs and to overcome the theoretical Betz limit is the introduction of a converging – diverging casing around the turbine. To further improve the performance of the diffuser a flange is placed at its outlet, which smoothes the flow along the diffuser interior, allowing larger diffusion angles to be utilized. The purpose of this research work is the aerodynamic design and computational analysis of such an arrangement with the use of Computational Fluid Dynamics (CFD). First, a HAWT rotor rotating at 600 RPM was designed with the use of the Blade Element Momentum (BEM) method. The three rotor blades are constructed using the NREL airfoil sections family S833, S834 and S835. The power coefficient of the rotor was optimised in a wind speed range of 5 – 10 m/s, with a maximum value of 0.45 for a wind speed of 7m/s. A full three-dimensional CFD analysis was carried out for the modeling of the flow around the rotor and through the flanged diffuser. The computational domain consisted of two regions with different frames of reference (a stationary and a rotating). The rotating frame rotates at 600 RPM and includes the rotor with the blades. All the simulations were performed using the commercial CFD software package ANSYS CFX. The Shear Stress Transport turbulence model was used for the simulations. Detailed flow analysis results are presented, dealing with the various investigated test cases, a) isolated turbine rotor, b) diffuser without the presence of the turbine, and c) the full turbine – diffuser arrangement for different flange heights and wind speeds. By varying the height of the flange and the wind speed, the effects of the above on the flow field and the power coefficient of the turbine were studied. The CFD resulting power coefficients are also compared and good agreement with existing in the literature experimental data was obtained. The results showed that there is a significant improvement in the performance of the wind turbine (by a factor from 2 to 5 on power coefficient at high blade tip speed ratio) and the proposed modification is particularly attractive for small wind turbines. The particular characteristics of the flow field, that are responsible for this improvement are identified and analysed in detail offering a better understanding of the physical processes involved.

Performance Prediction of Darrieus Turbine Through Numerical Analysis

2015 ◽  
Author(s):  
Prasenjit Mukherjee ◽  
Ujjwal K. Saha
Keyword(s):  
Wind Turbine ◽  
Azimuthal Angle ◽  
Boundary Layer Separation ◽  
Vital Role ◽  
Rotor Blades ◽  
Speed Ratio ◽  
Stream Velocity ◽  
Two Dimensional ◽  
Ansys Fluent ◽  
Blade Thickness

With the rising fossil-fuel prices, energy scarcity and climate-change, renewable energy plays an important role in producing local, clean and inexhaustible energy source to supply world rising demand for electricity. The selection of suitable wind turbine plays a vital role for urban power generation where wind is characterised by unsteadiness and turbulence. Thus, blade aerodynamics of wind turbine has a significant effect on turbine efficiency. In this study, the aerodynamic aspect of a straight bladed Darrieus turbine is numerically analyzed. Two dimensional numerical modelling and simulation of unsteady flow through the rotor blades (NACA 0018) of the turbine is performed using ANSYS FLUENT 14.5. The unsteady Reynolds averaged Navier-Stokes (RANS) equation is used to demonstrate the effects on the performance of two dimensional Darrieus turbine blade. The Shear Stress Transport (SST) k-ω model has been adopted for the turbulence closure. For the proposed analysis, the flow field characteristics are investigated at different azimuthal angle and tip speed ratio. Further, the parametric quantities such as solidity, number of blades and blade thickness have being investigated for a uniform free stream velocity of 6 m/s. The effect of laminar boundary layer separation on performance of the Darrieus turbine has also been taken into account during the study of flow physics around the blade. The results obtained are compared with the reported experimental and computational data.

scholarly journals Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation

2021 ◽  
pp. 1475472X2110551
Author(s):  
Aya Aihara ◽  
Karl Bolin ◽  
Anders Goude ◽  
Hans Bernhoff
Keyword(s):  
Large Eddy Simulation ◽  
Wind Turbine ◽  
Sound Pressure ◽  
Vertical Axis ◽  
Low Noise ◽  
Speed Ratio ◽  
Acoustic Analogy ◽  
Vertical Axis Wind Turbine ◽  
Eddy Simulation ◽  
Large Eddy

This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

Direct Numerical Simulation of Nonlinear Secondary Instabilities on the Pressure Side of a Savonius Style Wind Turbine

2016 ◽  
Author(s):  
Antoine Ducoin ◽  
Sukanta Roy ◽  
Mostafa Safdari Shadloo
Keyword(s):  
Energy Conversion ◽  
Wind Turbine ◽  
Vortex Shedding ◽  
Suction Side ◽  
Wake Flow ◽  
Transition To Turbulence ◽  
Speed Ratio ◽  
Small Scale ◽  
Computational Domain ◽  
Pressure Side

Savonius-style wind turbines are a class of vertical axis wind turbine usually used for off-grid applications. It appears to be promising for energy conversion because of its better self-starting capability and flexible design promises. The blades are characterized by relatively large surface, which are thin circular shape to produce large drag, which is used for power generation. Typically, the suction side of the advancing blade is submitted to strong adverse pressure gradient, causing a well known vortex shedding process, which is responsible for the wake flow. This topic has been the subject of many researches in the past decades, as it obviously depends on tip speed ratio (TSR) and directly influences the turbine efficiency. The flow on the pressure side of the blade is generally considered as fully attached and is characterized by high pressure, low velocity level that produces most of the drag used in the energy conversion. However, because of the gap between the two blades, the flow is accelerated on the pressure side of the returning blade and a thicker boundary layer develops at this side. Because of the concave curvature of the blade and the small scale of the turbine, centrifugal instabilities may occurs, depending on the flow regime that can cause natural transition on the blade. Moreover, these vortices induce different mechanisms of ejections and sweeps, causing thereby strong transverse variations of the drag coefficient, which results in the formation of hot spots near solid walls. This can leads to a rapid degradation of mechanical structures and materials fatigue. In this paper, Direct Numerical Simulations (DNS) are carried out in order to capture the flow instabilities and transition to turbulence occurring on the pressure of a conventional design Savonius wind turbine blade. Simulations are conducted with the open source code Nek5000, solving the incompressible Navier-Stokes equations with a high order, spectral element method. Because of the relatively high Reynolds numbers considered (Reξ = 90,000), the computational domain of the Savonius blade is reduced to the pressure side, whereas no turbine rotation is considered, which avoid the large scale vortex shedding that occurs on the suction side. The results suggest that Gortler vortices can occurs and cause the flow to transit to turbulence, which modify the pressure distribution and the drag force significantly.

The Influence of Sea Waves on Offshore Wind Turbine Aerodynamics

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
A. AlSam ◽  
R. Szasz ◽  
J. Revstedt
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Offshore Wind ◽  
Speed Ratio ◽  
Offshore Wind Turbine ◽  
Intensity Level ◽  
Sea Waves ◽  
Power Extraction ◽  
Wind Turbine Aerodynamics ◽  
Large Eddy

The impacts of swells on the atmospheric boundary layer (ABL) flows and by this on the standalone offshore wind turbine (WT) performance are investigated by using large eddy simulations (LES) and actuator-line techniques. At high swell to wind speed ratio, the swell-induced stress reduces the total wind stress resulting in higher wind velocity, less wind shear, and lower turbulence intensity level. These effects increase by increasing swell to wind speed ratio (C/U) and/or swell steepness. Moreover, for the same hub-height wind speed (Uhub), the presence of swells increases the turbine power extraction rate by about 3% and 8.4% for C/Uhub = 1.53 and 2.17, respectively.

scholarly journals The effect of using winglets to enhance the performance of swept blades of a horizontal axis wind turbine

2019 ◽  
Vol 11 (9) ◽  
pp. 168781401987831 ◽  
Author(s):  
Mohamed G Khalafallah ◽  
Abdelnaby M Ahmed ◽  
Mohamed K Emam
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Turbine ◽  
Twist Angle ◽  
Three Dimensional ◽  
Horizontal Axis ◽  
Cfd Modeling ◽  
Speed Ratio ◽  
Computational Domain ◽  
Horizontal Axis Wind Turbine

One of the recent methods to improve the performance of horizontal axis wind turbine is to attach a winglet at the tip of the blade of these turbines. Winglets reduce the effect of vortex flow at the blade tip and thus improve the performance of the blade. This article presents a parametric study using the computational fluid dynamics (CFD) modeling to investigate the capability of a winglet to increase the turbine power of swept blades as well as straight blades of a horizontal axis wind turbine. The effects of winglet direction, cant angle, and twist angle are studied for two winglet orientations: upstream and downstream directions. The numerical simulation was performed using ANSYS Fluent computational fluid dynamics code. A three-dimensional computational domain, cylindrical rotationally periodic, was used in the computations. The k-ω shear-stress transport turbulence model was adopted to demonstrate turbulence in the flow. Results show that horizontal axis wind turbine with winglet and sweep could enhance more power compared to their equivalent straight or swept blade. The best improvement in the coefficient of power is 4.39% at design tip speed ratio. This is achieved for downstream swept blades with winglets pointing in the upstream direction and having cant and twist angles of 40° and 10°, respectively.

scholarly journals Numerical investigation on the performance of a small counter-rotating wind turbine

2019 ◽  
Vol 116 ◽  
pp. 00055 ◽  
Author(s):  
Michał Pacholczyk ◽  
Krzysztof Blecharz ◽  
Dariusz Karkosiński
Keyword(s):  
Wind Turbine ◽  
Dynamic Interaction ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Computational Domain ◽  
Tip Speed Ratio ◽  
Noticeable Increase ◽  
Study Results ◽  
Constant Distance ◽  
Significant Interference

The article presents results of the investigation on the performance of a small counter-rotating wind turbine. Wind turbine has been simulated using Computational Fluid Dynamics methods. Actuator Line Model has been successfully used to represent rotors in computational domain. Parametric study has been carried out, taking into account changes in the tip speed ratio of the rotors while maintaining a constant distance between upwind and downwind rotor. Study results revealed noticeable increase in power coefficient for optimal configuration. Dynamic interaction between rotors has been investigated exposing no significant interference in both torque and power.

scholarly journals THE EFFECT OF NUMBER OF BLADES EXPERIMENTALLY ON THE HORIZONTAL WIND TURBINE SPEED

2021 ◽  
Vol 25 (Special) ◽  
pp. 2-1-2-8
Author(s):  
Aiya N. Hussein ◽  
◽  
Basim A. Sadkhan ◽  
Keyword(s):  
Wind Turbine ◽  
Wind Velocity ◽  
Rotational Speed ◽  
Rotor Blades ◽  
Horizontal Wind ◽  
Speed Ratio ◽  
High Wind ◽  
Tip Speed Ratio ◽  
Turbine Speed ◽  
Turbine Design

The aim of this research is to find the effect of the number of blades on the wind turbine speed and to find which number of blades is suitable for low wind areas and high wind areas. In wind turbine design; the number of blades, tip speed ratio, and the rotational speed of the rotor are the most important factors. At first, the tip speed ratio and the number of blades must be selected. The power of a wind turbine generator depends on the rotational speed of the rotor. The increase in wind velocity leads to an increase in the rotor speed. At wind velocity 2.36m/s, the rotational speed of 6 blades, 4 blades and 3 blades was 288, 54, and 34 rpm respectively. And, at wind velocity 13.85m/s, the rotational speed of 6 blades, 4 blades, and 3 blades are 1856, 2220, and 2103 rpm respectively. So, when the number of blades decreases, the rotational speed will increase at high wind velocity. But, at low wind velocity, the rotational speed is more effective when the number of blades increases. So, 6 rotor blades were found as suitable for low wind velocity areas as in Iraq.

scholarly journals Flow-driven simulation on variation diameter of counter rotating wind turbines rotor

2018 ◽  
Vol 154 ◽  
pp. 01111
Author(s):  
Y. Fredrika Littik ◽  
Y. Heru Irawan ◽  
M. Agung Bramantya
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Angular Velocity ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Speed Ratio ◽  
Axial Distance ◽  
Horizontal Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Computational Fluid Dynamics Cfd

Wind turbines model in this paper developed from horizontal axis wind turbine propeller with single rotor (HAWT). This research aims to investigating the influence of front rotor diameter variation (D1) with rear rotor (D2) to the angular velocity optimal (ω) and tip speed ratio (TSR) on counter rotating wind turbines (CRWT). The method used transient 3D simulation with computational fluid dynamics (CFD) to perform the aerodynamics characteristic of rotor wind turbines. The counter rotating wind turbines (CRWT) is designed with front rotor diameter of 0.23 m and rear rotor diameter of 0.40 m. In this research, the wind velocity is 4.2 m/s and variation ratio between front rotor and rear rotor (D1/D2) are 0.65; 0.80; 1.20; 1.40; and 1.60 with axial distance (Z/D2) 0.20 m. The result of this research indicated that the variation diameter on front rotor influence the aerodynamics performance of counter rotating wind turbines.

Calculating the aerodynamics of vertical axis wind turbines

2012 ◽  
Vol 34 (3) ◽  
pp. 169-184 ◽  
Author(s):  
Hoang Thi Bich Ngoc
Keyword(s):  
Wind Turbine ◽  
Incidence Angle ◽  
Vertical Axis ◽  
Rotor Blades ◽  
Vertical Axis Wind Turbine ◽  
Horizontal Axis Wind Turbine ◽  
Velocity Triangle ◽  
Relationship Of ◽  
The Relationship

Vertical axis wind turbine technology has been applied last years, very long after horizontal axis wind turbine technology. Aerodynamic problems of vertical axis wind machines are discussible. An important problem is the determination of the incidence law in the interaction between wind and rotor blades. The focus of the work is to establish equations of the incidence depending on the blade azimuth, and to solve them. From these results, aerodynamic torques and power can be calculated. The incidence angle is a parameter of velocity triangle, and both the factors depend not only on the blade azimuth but also on the ratio of rotational speed and horizontal speed. The built computational program allows theoretically selecting the relationship of geometric parameters of wind turbine in accordance with requirements on power, wind speed and installation conditions.

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