Commercially available wind-turbines are optimized to operate at certain wind velocity, known as rated wind velocity. For other values of wind velocity, it has different output which is lower than the rated output of the wind plant. Wind mill can be designed to provide maximum power output at different wind velocities through modification of swept area to match with the wind speed available at the moment. This can result in higher power output at all the velocities except that at rated wind speed because of limitation of generator. This results in increased utilization of generation capacity of wind mill compared to its commercially designed counterpart. A theoretical simulation has been done to prove a new concept about swept area of wind turbine blade which results in a significant increase in the power output through the year. Simulation results of power extracted through normal wind blade design and new concept are studied and compared. The findings of the study are presented in graphical and tabular form. Study establishes that there can be a significant gain in the power output with the new concept.
Wind turbine generators are producing power by exchanging momentum with air particles in motion. While harnessing wind energy, wind turbine does not damage environment and is a clean source of energy. As per CEA 2013 report, 8% of the installed power plant capacity is to be attributed to the wind energy installation. This only contributes 1.6% of total electricity generation [
Wind turbines are selected based on operating conditions of site. In other words, wind turbines are designed to provide maximum power for maximum occurring wind speed for which rotor and turbine are optimized and tested for. Like any other renewable energy sources, wind energy also has different intensity during different parts of the day and also for different months. With decline in wind energy, output decreases, below cut-off wind speed, output reduces proportionately till cut-in wind speed and thereafter no generation can be found. This is because at this instance momentum of wind particle is insufficient to rotate wind turbine and hence generator. The power output is proportional to the swept area of the blade and also to the pitch angle. During field conditions, momentum and RPM of turbine are adjusted to provide optimum torque and rpm. Traditionally, this is done by varying pitch angle and variable speed wind-turbine [
There are number of methods reported in literature on design optimization of wind mill [
To prove the new concept, new simulation is carried out using Q-Blade, V 8.0 software. This is open software developed by Hermann Fottinger Institute of Technical University (TU), Berlin. The software helps to evaluate the wind turbine blade profile on the basis of Blade Element Momentum theory. The main advantage with Blade Element Momentum theory is that it takes less time compared to that of Computational Fluid Dynamic analysis. Because of this advantage, a rapid evaluation of various blade designs is possible. The software helps user instantly to design the custom aerofoil and compute the performance polar and also has the capability to directly include the new design into rotor and simulate the power output of the wind generator. The software has necessary functions to simulate blades for HAWT and VAWT as well. NREL wind turbine model that is available in software library has been taken as reference blade design for further modifications. The blade profile that exist in Q-Blade V 8.0 trial version for NREL-5MW are provided in
The first column indicates normal profile of original blade with 63 m radius, used as reference profile. Subsequent columns indicate the blade profile modified for its radius with radius of 70 m, modified blade profile of 63 m blade with increased chord, 71.5 m blade profile with increased chord from tip to root in five sectors respectively. Increase in radius of reference blade was restricted to 71.5 m, in order not to exceed the critical radius that defines the fatigue strength of the blade. The Blade profile diagrams are shown in
As per Actuator Disc concept, analysis of the aerodynamic behavior of wind turbines can be done without any specific turbine design but through Energy Extraction Process. In
Normal | Increased radius | Increased chord | Increased radius & chord | ||||
---|---|---|---|---|---|---|---|
Length | Chord | Length | Chord | Length | Chord | Length | Chord |
0.00 | 3.20 | 0.00 | 3.20 | 0.00 | 3.20 | 0.00 | 3.20 |
1.36 | 3.54 | 1.36 | 3.54 | 1.36 | 3.54 | 1.36 | 3.54 |
4.10 | 3.85 | 4.10 | 3.85 | 4.10 | 3.85 | 4.10 | 3.85 |
6.83 | 4.17 | 6.83 | 4.17 | 6.83 | 4.17 | 6.83 | 4.17 |
10.25 | 4.55 | 10.25 | 4.55 | 10.25 | 4.55 | 10.25 | 4.55 |
14.35 | 4.65 | 14.35 | 4.65 | 14.35 | 4.65 | 14.35 | 4.65 |
18.45 | 4.46 | 18.45 | 4.46 | 18.45 | 4.46 | 18.45 | 4.46 |
22.55 | 4.25 | 22.55 | 4.25 | 22.55 | 4.25 | 22.55 | 4.25 |
26.65 | 4.01 | 26.65 | 4.01 | 26.65 | 4.01 | 26.65 | 4.01 |
30.75 | 3.75 | 30.75 | 3.75 | 30.75 | 3.75 | 30.75 | 3.75 |
34.85 | 3.50 | 34.85 | 3.50 | 34.85 | 3.50 | 34.85 | 3.50 |
38.95 | 3.26 | 38.95 | 3.26 | 38.95 | 3.26 | 38.95 | 3.26 |
43.05 | 3.01 | 43.05 | 3.01 | 43.05 | 3.01 | 43.05 | 3.01 |
47.15 | 2.76 | 47.15 | 2.76 | 47.15 | 2.76 | 47.15 | 2.76 |
51.25 | 2.52 | 51.25 | 2.52 | 51.25 | 4.55 | 51.25 | 4.55 |
54.67 | 2.31 | 54.67 | 2.31 | 54.67 | 4.17 | 54.67 | 4.17 |
57.40 | 2.09 | 57.40 | 2.09 | 57.40 | 3.85 | 57.40 | 3.85 |
60.13 | 1.40 | 60.13 | 1.40 | 60.13 | 3.54 | 60.13 | 3.54 |
61.50 | 0.70 | 70.00 | 0.70 | 61.50 | 3.20 | 70.00 | 3.20 |
*All dimensions are in meter.
that of the disc and an area larger than the disc downstream. The expansion of the stream-tube is because the mass flow rate must be the same everywhere. The mass of air which passes through a given cross section of the stream-tube in a unit length of time is
The symbol
The wind energy after actuator disc is given by,
It is usual to consider that the actuator disc induces a velocity variation which must be superimposed on the free-stream velocity. The stream-wise component of this induced flow at the disc is given by
Following the momentum theory using the Bernoulli’s principle applied to the upstream and downstream sections of the stream tube, separate equations are calculated for energy upstream and downstream as the total
energy is different for both the streams. From further calculations we derive Equation (1).
Using Equations (1) & (3), we obtain
As this force is concentrated at the actuator disc the rate of work done by the force is
The power coefficient is defined as
The coefficient of power
The percentage increase in power output for different radius (s) in steps of 2 m from 63 m radius as reference blade are simulated against power output and summarized in
Similarly, percentage gain in output power delivered according to the chord variations is summarized in
A graph demonstrating measurements, taken by Mark Dawson et al., for extended length (only), wind blade design is reproduced here in
Wind speed | Existing radius―63 m | Radius―64.5 m | Radius―66.5 m | Radius―68.5 m | Radius―71.5 m | Benefit over existing |
---|---|---|---|---|---|---|
3 | 1.0 | 1.1 | 1.2 | 1.2 | 1.3 | 25.42892 |
4 | 3.8 | 4.2 | 4.4 | 4.4 | 4.8 | 26.60006 |
5 | 8.5 | 9.5 | 10.0 | 10.0 | 10.8 | 26.94602 |
6 | 15.5 | 17.5 | 18.4 | 18.4 | 19.8 | 27.21183 |
7 | 24.9 | 27.8 | 29.1 | 29.1 | 31.2 | 25.19004 |
8 | 37.2 | 41.3 | 44.1 | 44.1 | 47.2 | 27.05546 |
9 | 52.9 | 59.3 | 62.7 | 62.7 | 66.6 | 25.87414 |
10 | 72.4 | 80.3 | 84.1 | 84.1 | 90.1 | 24.45874 |
11 | 95.9 | 100.0 | 100.0 | 100.0 | 100.0 | 4.30885 |
12 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0 |
13 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0 |
14 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 0 |
*All values are in percentage (%) of simulated output against output for reference turbine at rated capacity.
Wind speed | Radius & Chord―63 m & from tip to root by 21% proportionately till five steps | Chord―from tip to root by 21% proportionately till five steps |
---|---|---|
3 | 0.0 | 0.1 |
4 | 3.3 | 2.9 |
5 | 9.3 | 0.8 |
6 | 18.4 | 14.9 |
7 | 30.6 | 24.4 |
8 | 45.7 | 36.6 |
9 | 46.2 | 52.2 |
10 | 89.8 | 71.7 |
11 | 100.0 | 95.6 |
12 | 100.0 | 100.0 |
13 | 100.0 | 100.0 |
14 | 100.0 | 100.0 |
*All values are in percentage (%) of simulated output against output for reference turbine at rated capacity.
In
The right extreme line (red color) in
The simulation results confirm significant gain in power output corresponding to the increase in radius of the rotor alone. Maximum gain of 27% is observed for radius equivalent to the critical radius i.e. 71.5 m compared to the radius of reference rotor i.e. 63 m. There is no gain observed for increase in the chord of the blade alone.
Best results are obtained when both chord and radius both are increased simultaneously. It can be inferred that the wind turbine shown promising results for the output power generated at both the lower and higher wind speed. Major impact observed in the generator reaches the synchronous speed at an earlier (i.e., at lower than the rated wind speed) stage than the existing.
Output of the wind turbine increases with increase in chord radius (length of blade) at all wind velocities; the power output becomes maximum at rated wind velocity. Thereafter output is stable for any wind velocity up to cut-off wind velocity. Higher gains can be obtained with more increase in blade length from lower to higher wind speed. It is possible to achieve state of rated power output at comparatively lower wind velocity than the rated wind velocity by increasing swept area. That means, more power can be harnessed on yearly basis. We can logically conclude that reduction in swept area can also generate power from wind mill above cut-off wind velocities wherein otherwise wind mill will stop for safety. Trend in both the cases matches well with each other.
Additional gain can be obtained by increasing width also proportionately which is not experimented before. It can be concluded that in order to gain more output from wind turbine, complete aerodynamic shape should be changed. We recommend that experiments need to be conducted on the basis of these simulation studies to identify the percentage gain and also to identify practical constraints that can lower the gain.
Authors like to acknowledge management team of Gujarat Energy Research & Management Institute (GERMI), Gandhinagar for providing all necessary support to conduct present study. Special acknowledgements to Vice Chairman & Managing Trusty (VGMT)―GERMI and Managing Director of M/s. Gujarat State Petroleum Corporation (GSPC), Gandhinagar for providing necessary funding under Summer Internship Project (SIP) scheme.