scholarly journals Effect of Ambient Reynolds Number on Small Wind Turbine Subjected to Low Wind Speed Conditions

2021 ◽  
Vol 12 (2) ◽  
pp. 223-231
Author(s):  
Joel Mbwiga ◽  
Cuthbert Z Kimambo ◽  
Joseph Kihedu
Keyword(s):  
Reynolds Number ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Power Performance ◽  
Airfoil Surface ◽  
Small Wind Turbine ◽  
Low Wind Speed ◽  
The Difference

Wind flow over the airfoil surface is adversely affected by the differences between the design and ambient values of a dimensionless quantity called Reynolds number. Wind turbine designed for high Reynolds Number shows lower maximum power performance when installed in low-speed wind regime. Tanzanian experience shows that some imported modern wind turbines depict lower power performance compared to the drag-type locally manufactured wind turbines. The most probable reason is the difference between design and local ambient Reynolds numbers. The turbine design parameters have their properties restricted to the range of Reynolds numbers for which the turbine was designed for. When a wind turbine designed for a certain range of Reynolds numbers is made to operate in the Reynolds number out of that range, it behaves differently from the embodied design specifications. The small wind turbine of higher Reynolds number will suffer low lift forces with probably occasional stalls.  

Drag Reduction Using Riblet Film Applied to Airfoils for Wind Turbines

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Agrim Sareen ◽  
Robert W. Deters ◽  
Steven P. Henry ◽  
Michael S. Selig
Keyword(s):  
Reynolds Number ◽  
Renewable Energy ◽  
Drag Reduction ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Angle Of Attack ◽  
Reynolds Numbers

This paper presents results of a study that was commissioned by the 3M Renewable Energy Division to measure the drag reduction by using riblet film on airfoils specifically designed for wind turbine applications. The DU 96-W-180 airfoil was tested with four different symmetrical V-shaped riblet sizes (44, 62, 100, and 150-μm) at three Reynolds numbers (1 × 106, 1.5 × 106, and 1.85 × 106) and at angles of attack spanning the low drag range of the airfoil. Tests were run with riblet film covering different sections of the airfoil in order to determine the optimal riblet location in terms of drag reduction. Results showed that the magnitude of drag reduction depended on the angle of attack, Reynolds number, riblet size, and riblet location. For some configurations, riblets produced significant drag reduction of up to 5%, while for others riblets were detrimental. Trends in the results indicated an optimum riblet size of 62-μm for the range of Reynolds numbers at which tests were conducted. The airfoil chord was 18 in (0.457 m). Results also showed that each riblet size performed best at a given Reynolds number with the optimal Reynolds number decreasing with an increase in riblet size.

Design of a Controllable One-Meter Scale Research Wind Turbine

2017 ◽  
Author(s):  
Samuel Cole ◽  
Gavin Hess ◽  
Martin Wosnik
Keyword(s):  
Reynolds Number ◽  
Wind Turbine ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Design Parameters ◽  
Speed Ratio ◽  
Flow Physics ◽  
Manual Adjustment ◽  
High Reynolds ◽  
Turbine Design

A research wind turbine of one meter diameter was designed for the UNH Flow Physics Facility (FPF), a very large flow physics quality turbulent boundary layer wind tunnel (W 6m, H 2.7m, L 72m), which provides excellent spatial and temporal resolution, low flow blockage and allows measurements of turbine wakes far downstream due its long fetch. The initial turbine design was carried out as an aero-servo model of the NREL 5MW reference turbine, with subsequent modifications to both the hub to accommodate blade mounting and pitch-adjustment, and increases in model blade chord to achieve sufficiently high Reynolds numbers. A trade-off study of turbine design parameters in scale space was conducted. Several candidate airfoil profiles were evaluated numerically with the goal to reach Reynolds-number independence in turbine performance in the target operating range. The model turbine will achieve Reynolds numbers based on blade chord, an important consideration for airfoil performance and near-wake evolution, greater than 100,000, and Reynolds numbers based on turbine diameter, important for far-wake transport, on the order of 1,000,000. The blockage ratio is less than 5% based on swept area. A motor and controller combination was implemented that allows to precisely prescribe the turbine tip-speed ratio (at maximum power coefficient for optimum blade chord), which can remain stable and absorb the generated electric power for long periods of time. The turbine nacelle was designed with a blade mounting mechanism which allows for precise manual adjustment of blade pitch angle, while allowing for future implementation of actuated pitch control. The O(1m) turbine scale is viewed as a cost-effective compromise between size, driven by the need for sufficiently high Reynolds number, and the need for detailed measurements for significant distances downstream of the turbine under controlled conditions.

scholarly journals Aerodynamic improvement of Darrieus wind turbine

2021 ◽  
Vol 897 (1) ◽  
pp. 012001
Author(s):  
Oleg Goman ◽  
Andrii Dreus ◽  
Anton Rozhkevych ◽  
Krystyna Heti
Keyword(s):  
Reynolds Number ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Structural Reliability ◽  
Vertical Axis ◽  
Vertical Wind ◽  
Integral Approach ◽  
Vertical Axis Wind Turbine ◽  
Calculation Algorithm ◽  
Vertical Axis Wind Turbines

Abstract Until recently, vertical-axis wind turbines are less extensively developed in wind energetics. At the same time, there are a number of advantages in turbines of such type like their independence from the change of wind direction, lower levels of aerodynamic and infrasound noises, higher structural reliability (compared to horizontal engines), etc. With these advantages, vertical-axis wind turbines demonstrate promising capacities. Inter alia, the productiveness of such turbines can be refined through the aerodynamic improvement of the structure and comprehensive optimization of the rotor geometry. The main purpose of the presented paper is to aerodynamically improve vertical wind turbine in order to increase the efficiency of wind energy conversion into electricity. Within the framework of the classical theory of impulses, this article presents a study of the effect of variation in Reynolds number on the general energy characteristics of a vertical-axis wind turbine with two blades. The integral approach makes it possible to use a single-disk impulse model to determine the main specific indicators of the system. The power factor was calculated based on the obtained value of the shaft torque factor, which in turn was determined by numerically integrating the total torque generated by the wind turbine. To calculate the test problem, we used the classic NACA airfoils: 0012, 0015, 0018 and 0021. The proposed calculation algorithm makes it possible not to indicate the Reynolds number and corresponding aerodynamic coefficients at the beginning of the calculation, but to recalculate it depending on the relative speed, position of the airfoil and the linear speed of the airfoil around the circumference. Proposed modern design techniques can be helpful for optimization of vertical wind turbines.

Computational Analysis of Airfoil Merging and its Effect on Performance of Lift Based Vertical Axis Wind Turbine

2016 ◽  
Author(s):  
Akshay Basavaraj
Keyword(s):  
Reynolds Number ◽  
Wind Turbine ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Vertical Axis ◽  
Aerodynamic Characteristics ◽  
Vertical Axis Wind Turbine ◽  
Low Wind Speed ◽  
Naca 0012 ◽  
Selection Of

In regions of low wind speed, overcoming the starting torque of a Vertical Axis Wind Turbine (VAWT) becomes a challenge aspect. In order to overcome this adversity, careful selection of airfoils for the turbine blades becomes a priority. This paper tries to address the issue utilizing an approach wherein by observing the effect of merging two airfoils. Two airfoils which are of varying camber and thickness are merged and their aerodynamic characteristics are evaluated using the software XFOIL 6.96. For a variation in angle of attack from 0 to 90°, aerodynamic analysis is done in order to observe the behavior of one quarter of the entire VAWT cycle. An objective function is developed so as to observe the maximum possible torque generated by these airfoils at Reynolds number varying from 15,000–120,000. Due to change in the value of CL observed at Low Reynolds Number using commercial CFD softwares, multiple objective functions are utilized to observe the behavior over a range of Reynolds number. An experimental co-relation between the cut-in velocity and the lift-coefficient of the airfoils is developed in order to predict the cut-in velocity of the interpolated airfoils. The airfoils used for this paper are NACA 0012, NACA 0018, FX 66 S196, Clark Y (smooth), PT 40, SD 7032, A 18, SD 7080, SG 6043 and SG 6040.

An almost-inviscid geostrophic flow

1962 ◽  
Vol 12 (1) ◽  
pp. 129-134 ◽  
Author(s):  
L. M. Hocking
Keyword(s):  
Reynolds Number ◽  
Fluid Velocity ◽  
Equations Of Motion ◽  
Axial Direction ◽  
Reynolds Numbers ◽  
Rigid Rotation ◽  
Velocity Variation ◽  
Geostrophic Flow ◽  
The Difference ◽  
Streaming Motion

An almost rigid rotation of a viscous fluid is produced by dividing the containing cylinder into two sections and rotating them at slightly different speeds. The fluid velocity can be separated into two parts, a swirl about the axis and a streaming motion in the axial planes. When the difference in the speeds of rotation of the two sections is small, the equations of motion can be linearized. The solution is found for large Reynolds numbers and provides an illustration of the way in which the conditions of geostrophic flow (no velocity variation in the axial direction and an inability to insist on undistrubed flow at infinity) are approached as the Reynolds number tends to infinity.

Small Wind Turbine Power Performance Testing with Uncertainty Analysis

2014 ◽  
Vol 875-877 ◽  
pp. 1944-1948
Author(s):  
Wen Lei Bai ◽  
Byun Gik Chang ◽  
Gerald Chen ◽  
Ken Starcher ◽  
David Carr ◽  
...  
Keyword(s):  
Wind Speed ◽  
Uncertainty Analysis ◽  
Wind Turbine ◽  
Performance Testing ◽  
Air Pressure ◽  
Power Performance ◽  
Small Wind Turbine ◽  
Uncertainty Sources ◽  
Measurement Uncertainties

Wind turbine power performance testing consists of power, temperature, air pressure and wind speed measurements collected for this study during which measuring uncertainties are involved. Due to the measurement uncertainties, the results of power performance testing are affected; therefore, it is necessary to consider the measurement uncertainties for evaluating the accuracy of turbine testing. For this purpose of this study, uncertainty analysis for one 5kW wind turbine power performance testing was conducted. The results of uncertainty analysis indicated that the uncertainty negatively affected the validity of conclusions drawn from power performance testing, and the uncertainty sources are various in different wind speed bins.

Wake Analysis of a Finite Width Gurney Flap

2015 ◽  
Author(s):  
D. Holst ◽  
A. B. Bach ◽  
C. N. Nayeri ◽  
C. O. Paschereit ◽  
G. Pechlivanoglou
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Tip Vortex ◽  
Finite Width ◽  
Low Reynolds Numbers ◽  
Gurney Flaps ◽  
Gurney Flap ◽  
Pitch System

The results of stereo Particle-Image-Velocimetry measurements are presented in this paper to gain further insight into the wake of a finite width Gurney flap. It is attached to an FX 63-137 airfoil which is known for a very good performance at low Reynolds numbers and is therefore used for small wind turbines and is most appropriate for tests in the low speed wind tunnel presented in this study. The Gurney flaps are a promising concept for load control on wind turbines but can have adverse side effects, e.g. shedding of additional vortices. The investigation focuses on frequencies and velocity distributions in the wake as well as on the structure of the induced tip vortices. Phase averaged velocity fields are derived of a Proper-Orthogonal-Decomposition based on the stereo PIV measurements. Additional hot-wire measurements were conducted to analyze the fluctuations downstream of the finite width Gurney flaps. Experiments indicate a general tip vortex structure that is independent from flap length but altered by the periodic shedding downstream of the flap. The influence of Gurney flaps on a small wind turbine is investigated by simulating a small 40 kW turbine in Q-Blade. They can serve as power control without the need of an active pitch system and the starting performance is additionally improved. The application of Gurney flaps imply tonal frequencies in the wake of the blade. Simulation results are used to estimate the resulting frequencies. However, the solution of Gurney flaps is a good candidate for large scale wind turbine implementation as well. A FAST simulation of the NREL 5MW turbine is used to generate realistic time series of the lift. The estimations of control capabilities predict a reduction in the standard deviation of the lift of up to 65%. Therefore finite width Gurney flaps are promising to extend the lifetime of future wind turbines.

scholarly journals An experimental study of the optimal design parameters of a wind power tower used to improve the performance of vertical axis wind turbines

2018 ◽  
Vol 10 (9) ◽  
pp. 168781401879954
Author(s):  
Soo-Yong Cho ◽  
Sang-Kyu Choi ◽  
Jin-Gyun Kim ◽  
Chong-Hyun Cho
Keyword(s):  
Experimental Study ◽  
Optimal Design ◽  
Wind Turbine ◽  
Wind Power ◽  
Wind Turbines ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Design Parameters ◽  
Vertical Axis Wind Turbine ◽  
Vertical Axis Wind Turbines

In order to augment the performance of vertical axis wind turbines, wind power towers have been used because they increase the frontal area. Typically, the wind power tower is installed as a circular column around a vertical axis wind turbine because the vertical axis wind turbine should be operated in an omnidirectional wind. As a result, the performance of the vertical axis wind turbine depends on the design parameters of the wind power tower. An experimental study was conducted in a wind tunnel to investigate the optimal design parameters of the wind power tower. Three different sizes of guide walls were applied to test with various wind power tower design parameters. The tested vertical axis wind turbine consisted of three blades of the NACA0018 profile and its solidity was 0.5. In order to simulate the operation in omnidirectional winds, the wind power tower was fabricated to be rotated. The performance of the vertical axis wind turbine was severely varied depending on the azimuthal location of the wind power tower. Comparison of the performance of the vertical axis wind turbine was performed based on the power coefficient obtained by averaging for the one periodic azimuth angle. The optimal design parameters were estimated using the results obtained under equal experimental conditions. When the non-dimensional inner gap was 0.3, the performance of the vertical axis wind turbine was better than any other gaps.

scholarly journals Aerodynamics of Flapping Wing at Low Reynolds Numbers: Force Measurement and Flow Visualization

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Abhijit Banerjee ◽  
Saurav K. Ghosh ◽  
Debopam Das
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flow Visualization ◽  
Force Measurement ◽  
Reynolds Numbers ◽  
Flapping Flight ◽  
Water Tank ◽  
Cross Sectional ◽  
Piv Measurement ◽  
The Difference

Flow field of a butterfly mimicking flapping model with plan form of various shapes and butterfly-shaped wings is studied. The nature of the unsteady flow and embedded vortical structures are obtained at chord cross-sectional plane of the scaled wings to understand the dynamics of insect flapping flight. Flow visualization and PIV experiments are carried out for the better understanding of the flow field. The model being studied has a single degree of freedom of flapping. The wing flexibility adds another degree to a certain extent introducing feathering effect in the kinematics. The mechanisms that produce high lift and considerable thrust during the flapping motion are identified. The effect of the Reynolds number on the flapping flight is studied by varying the wing size and the flapping frequency. Force measurements are carried out to study the variations of lift forces in the Reynolds number (Re) range of 3000 to 7000. Force experiments are conducted both at zero and finite forward velocity in a wind tunnel. Flow visualization as well as PIV measurement is conducted only at zero forward velocity in a stagnant water tank and in air, respectively. The aim here is to measure the aerodynamic lift force and visualize the flow field and notice the difference with different Reynolds number (Re), and flapping frequency (f), and advance ratios (J=U∞/2ϕfR).

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