OPTIMIZATION OF FLOATING HORIZONTAL AXIS WIND TURBINE (FHAWT) BLADES FOR AERODYNAMIC PERFORMANCE MEASUREMENT

Abstract

The purpose of this paper is to find the effect of angle of attack towards the blade of Floating Horizontal Axis Wind Turbine (FHAWT) and optimize to get the best blade performance in between twisted and untwisted blade which will give maximum lift and drag force ratio. The optimization of the FHAWT blades are carried out by analysing, modelling and simulation by using simplified spreadsheet method, CFD analysis in ANSYS WORKBENCH 2020 R1 software and wind tunnel testing.

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OPTIMIZATION OF FLOATING HORIZONTAL AXIS WIND TURBINE (FHAWT)
BLADES FOR AERODYNAMIC PERFORMANCE MEASUREMENT
Sajid Ahammed
School of Engineering, UOW Malaysia KDU University College,
Utropolis Glenmarie, ShahAlam, Malaysia.
* 0116915@kdu-online.com
ABSTRACT
Wind power is one of the most important sources of renewable energy which extract kinetic energy from the
wind. Currently much research has concentrated on improving the aerodynamic performance of wind turbine
blade through wind tunnel testing and theoretical studies. However, wind turbine simulation through
Computational Fluid Dynamics (CFD) software offers inexpensive solutions to aerodynamic blade analysis
problem. The purpose of this paper is to find the effect of angle of attack towards the blade of Floating
Horizontal Axis Wind Turbine (FHAWT) and optimize to get the best blade performance in between twisted
and untwisted blade which will give maximum lift and drag force ratio. The optimization of the FHAWT
blades are carried out by analysing, modelling and simulation by using simplified spreadsheet method, CFD
analysis in ANSYS WORKBENCH 2020 R1 software and wind tunnel testing. The blades are evaluated
regarding their lift and drag force ratio in different angle of attack and wind speed. The results, obtained
from both computer programs, wind tunnel testing and the initial hand calculations, are comparable and
satisfying. Finally, the model was implemented to optimize blades performance, especially at low wind
velocities, which is crucial to produce power during operating in offshore environment.
Keywords: Aerodynamic, Angle of Attack, Optimization, wind tunnel, Lift force, drag force.
INTRODUCTION
In this modern world to generate electricity from offshore wind turbines has become famous by the Floating
Horizontal Axis Wind Turbine (FHAWT)[1]. Wind turbine is a device that converts wind energy from
kinetic energy to electrical energy. There are two types of wind turbine which is vertical axis wind turbine
(VAWT) and horizontal axis wind turbine (HAWT). In figure 1-1 the difference between HAWT and
VAWT has shown [2].
Figure 1.1: HAWT VS. VAWT Design [2].
While designing the Floating Horizontal Axis Wind Turbine (FHAWT) blade profile, blade taper, tip loss,
variable wind speed and angle of attack place an important role. The angle of attack plays an important role
towards the blade of wind turbine which should be investigated and optimized to get the best performance of
FHAWT. When the wind turbine operates in wind flows, the angle of attack (AOA) of a given blade varies

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at different azimuths. The AOA of the blade is one of the most dominating parameters for the wind turbine
control and the blade design. As the AOA fluctuates in flows, the aerodynamics of the operating wind
turbine is significantly influenced. On the one hand, the aerodynamic loads of the blades are closely related
to the AOA. At each blade section, the aerodynamic forces are calculated based on the AOA and the inflow
velocity. Generally, the lift force increases with the AOA in the attached flow state while decreases with the
further increase of the AOA once the stall angle is exceeded. The blades suffer from larger aerodynamic
loads and bending moments since the blades experience larger increase in lift due to the dynamic stall. The
low efficiency due to low lift and drag ratio is one of the main problem found in FHAWT.
To find out the best blade performance between twisted and untwisted blade and which will give the
maximum lift to drag force ratio lift was measured directly from the force balance. It is known that the
maximum power efficiency is achieved when the blade is twisted according to a program that depends upon
the variation of the sectional lift and drag coefficients with angle of attack. Results for a typical air foil
cross-section show that the optimum angle of attack and optimum twist angle of the blade improves the
performance of the wind turbine.
METHODOLOGY
The process started with brainstorming and getting the idea of FHAWT. After that need to select the air foil
for FHAWT and considering the designing parameter. Then need to design the turbine and floating platform.
After that need to finalize the platform and whole turbine design. Then simulation of FHAWT will be done
in ANSYS. Then can analyze and compare the optimization of FHAWT. If the result shows the optimization
done, then the aim and objective will be achieved. After that need to fabricate the FHAWT. Optimization of
FHAWT is done. The flow chart of methodology is given in Figure 2.1
Figure 2.1 The flow chart of methodology

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2.1 Design procedure outline
There is a ramification of various techniques that may be taken in wind turbine layout and therefore there are
also some of issues that need to be taken into account. The layout method outlined in “(McGowan, 2003),
sets tips for the layout of a wind power converter and has been taken into consideration for application in
this venture.
2.2 Air foil selection
Mach range and Reynolds number need to be defined, before introducing the airfoil behavior. Mach number
is a ratio of speed of an object over, Sound and its speed defined as following equations [3] :
Where Ma is Mach number, vs is object speed and uc is sound speed. Subsonic is defined as, transonic is
defined as, supersonic is defined as and hypersonic is defined as. Mach<=1, transonic is Mach =1,
supersonic is Mach >=1, hypersonic Mach >=5
The Reynolds number is a non-dimensional value and it is a ratio of inertial force to viscous force, defined
as:
Aerofoil behavior can be described into 3 float regimes: the attached float regime, the high lift/stall
improvement regime and the flat plate/completely stalled regime [4]. According to Witcher, Witcher and
Harding for efficient blade will have high lift to drag ratio. NACA 4- digit series will have given the good
performance at low speed. Therefore, choose the NACA 6409 blade air foil for analysis. These profiles
given the better performance at low speed having high lift to drag ratio and good stall properties.
Specification of NACA 6409 [5] low speed wind blade profile –
 Max thickness 9% at 29.3% chord.
 Max camber 6% at 39.6% chord Source [6]
Figure 2.2: Air foils important parameters[5] Figure2.3: NACA 6409 Comparison
[6]
Modelling and Analysis
The design process of the blade design of FHAWT has several steps. Where the blade will be redesigned by
using NACA 6409 air foil. The air foil coordinates have taken form Air Foil tools official website[5]. And
the data used for designing the blade such as cord length, angle of twist and the ratio of r/R has been taken
from the previous research paper by McGowan, Rodgers.[7]

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Table 3.1 Twist and chord distribution for a twisted blade [7]
By using the NACA 6409 air foil coordinates the three-dimensional air foil will be created in the solid
works. At first after starting the solid works need to select the front plane, then from reference geometry
select plane then create ten planes the distance between one plane to another plane will be 15.94mm. After
that from reference geometry need to select the curve through xyz plane then input the following coordinates
in the table given below. Then the air foil NACA 6409 will be created in solid works window in Figure 3.4.
After that need to select plane 1 and click edit button then need to convert the 3d air foil to 2d air foil in
Figure 3.5. By using same procedure ten air foil will be created in ten planes where the angle of twist and
cord length will be given according to the date given in Table 3.2.
Figure 3.1: Modelling process of FHAWT
The twisted blade FHAWT shown in Figure 3.16, where solid works model and engineering drawing are
shown with all dimension

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Figure 3.2 Engineering drawing of twisted blade of FHAWT
RESULT AND DISCUSSION
This chapter presents results from physical characterization tests (wind tunnel test), theoretical calculation
and ANSYS simulation data of the twisted blade of FHAWT turbine. The collected performance data will
then be compared to target performance curves and suggestions for a future model blade design will be
given. Firstly, theoretical calculation will be done by using the porotype data of the FHAWT to find drag
and lift forces at the speed of wind tunnel testing. Then simulation will be done in ANSYS WORKBENCH
2020 R1 software to find drag and lift forces of the model. Lastly the designed FHAWT twisted blade will
be tested in the wind tunnel and after that the lift force and the drag force will be collected at different angle
of attack and wind speed. The three different values will be compared to see the errors and the precisions of
the collected data. After that the errors of data among these experiment will be calculated to see the
preciseness of the data. Then the graph will be plotted and compared with the existing untwisted FHAWT’s
blade and find the best performance. The lift and drag force for FHAWT blades will be calculated from the
representative equation which are given below
L = ½ CL ρ v2 A ………… (1) and D =½CD ρ v2 A ………. (2)
Where, L = lifting force (N), D = drag force (N),
CD = drag coefficient, CL = lifting coefficient,
ρ = density of fluid (kg/m3), v = flow velocity (m/s),
A = body area (m2).
Now from equation can calculated the lift and drag force for the blade with the data of FHAWT blades.

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Calculation of FHAWT:
4.2 Simulation in ANSYS of FHAWT:
After running the calculation and completing 200 calculations the following iteration graph has been plotted
in the fluent window. Figure 5.0 shows the residual velocity graphs for 200 iterations in direction of
continuity, (x, y & z)-velocity, k and omega.
Figure 4.1: Residual velocity graphs of 200 iteration
4.2.1 Lift force plot
The lift force is plotted in the new window of the Workbench window and shows the result of lift force vs
iteration. Where it can see that the maximum lift for can get around 1.16N and the minimum lift force is
around -0.18N. The value varies between -0.18N-1.16N. The lift force is higher at 85 iteration point and
after 100 iterations it stays constant because of the constant balanced wind flow (can see from velocity
contour plot in next section 5.2.3) among the FHAWT blades. The average lift force after 90 iterations is
around 1.05N. do it is clear that when the velocity is constant and it attacks to blade evenly then the lift force
of the blades keeps constant as well. So the higher wind creates high lift force to the blade.

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Figure 4.2: Lift force vs. iteration graph IN ANSYS Fluent simulation.
4.2.2 Drag force plot
From the graphs it has seen that it is completely opposite of lift force graph. It is opposing the wind to pass
through the blades that’s why the values are negative. It changes with velocity of the wind and completely
opposite of lift force. When the lift force is high then the drag force is high as well. But because of the twist
distribution of the blade the drag force is quite low. Where the values vary from -0.034N to 0.07N. the
maximum drag force can get at 85 iteration point which is around -0.07N and minimum at beginning which
is around -0.034. the 100 iteration drag force becomes stable as well. Though it is totally opposite graph of
lift force but act similarly with the changes of iteration. The result mainly shows the low drag force than the
lift force.
Figure 4.3: Drag vs. iteration graph IN ANSYS Fluent simulation.
4.2.3 Contour plot
I. Velocity magnitude plot
Figure X and Y illustrates the isometric and top view of FHAWT blades plot, where it shows that when hits
the blade because twisting angle of the blade it can pass through easily and generate maximum lift force. As
the figure shows that the edge of the blade is highly affected to produce high lift force where the drag force
reduced. At the edge of the blade the velocity magnitude is around 1.35× 102 m/s which is maximum. It is
known from equation 5.1.1 that lift force is directly proportional to velocity. When the velocity is maximum
the lift force will be maximum as well.

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Figure 4.4: Velocity magnitude plot of FHAWT blades Figure 4.5: Top view of velocity magnitude plot.
Static Pressure Plot
Form Figure Z can come to an explanation that the static pressure acting on the blades in very less area and
the area affected by maximum static pressure which is around 8.26× 103 Pascal. It can also be noted that at
the front and edge of the blade low pressure distribution is observed because of twisted blade. It can attribute
that reverse flow and low pressure regions generated due to the twisted blade profile so the drag will be less.
Figure 4.6: Static pressure contour plot of FHAWT blades
4.3 Wind tunnel test of FHAWT
The testing of the FHAWT blade has been done in AF100 subsonic wind tunnel where the blades lift and
drag force has been collected in different velocities and angle of attack. Where (0,10,20,30,40,50,60,70 and
80) mmH2O dynamic pressure has been chosen and angle of attack (-10, -5,0,5,10,15,25 and 30) ° has been
selected to find the aerodynamics performance.
4.3.1 Wind tunnel testing data
The wind tunnel test has been performed in the velocity range and different angle of attack (-10, -
5,0,5,10,15,25 and 30) °. For different velocity and angle of attack the collected aerodynamic performance
data are shown in the table which is given below. Table 4.1 shows the data of lift and drag force at different

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angle of attack at wind speed 18.23m/s. Where lift force, drag force, pitching moment and L/D ratio has
tabulated and shows the relation with velocity and angle of attack.
Table 4.1: Lift different angle of attack at wind speed 18.23m/s
Figure 4.7 shows the graph of lift and drag vs angle of attack at wind speed 18.23m/s. Where the maximum
lift force is at 10° and minimum is at 0°. The maximum lift force is at 15° and minimum is at 0°. The drag
and lift force both changes at different angle of attack and velocity as well. The following Figure 4.8 shows
a relationship graph between L/D against angle of attack where the maximum L/D ratio can get around 20.5
at 10° angle of attack and minimum at 30°.
Figure 4.7 Lift and drag vs angle of attack at 18.23m/s Figure 4.8 Lift and drag ratio vs angel of
attack at 18.23m/s
Table 4.2 shows the data of lift and drag force at different angle of attack at wind speed 18.23m/s. Where lift
force, drag force, pitching moment and L/D ratio has tabulated and shows the relation with velocity and
angle of attack.

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Table 4.2: Lift and drag force at different angle of attack at wind speed 22.33m/s
In Figure 4.8 it represents the graph where the maximum lift force is 0.55N and minimum 0.30N obtained at
-5° and 30° angle of attack. The maximum and minimum drag force is 0.03N and 0.02N at 25° and -5° as
well. Where drag force shows a linear graph.
Figure 4.8 lift and drag vs angle of attack at speed 22.33m/s Figure 4.9 Lift and drag ratio vs angel of
attack at 22.33m/s
In Figure 4.9 the L/D ratio vs angle of attack graph has been plotted the maximum ratio have obtained 27.5
at -5° and minimum 13.3 at 15°. The ratio is higher between -10° to 10°. It has noticed because of increasing
velocity L/D ratio also increasing.
Table 4.3 shows the aerodynamic data at different angle of attack at wind speed 28.83m/s. From there the
graphs can be plotted and compare to understating the aerodynamic performances of FHAWT blades.
Table 4.3 Lift and drag force at different angle of attack at wind speed 28.83m/s

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From the graphs which has shown in Figure 4.9 it represents that the maximum lift force created at -10°
which is 0.88 and the minimum lift force 0.50N at 30°. Maximum drag force recorded 0.03N at -10° and
minimum is 0.02N at -5°.
Figure 4.9 Lift and drag vs angle of attack at speed 28.83m/s Figure 4.10 Lift and drag ratio vs angel of
attack at 28.83m/s.
In Figure 4.10 the maximum lift and rag ratio recorded 38 at 10° angle of attack and minimum at 15° angle
of attack. The graph shows a sinusoidal characteristic where the ration dropped after 10° angle of attack of
the twisted FHAWT blade.
In Table 4.4 lift and drag force, pitching moment and lift and drag ratio has recorded at different angle of
attack at wind speed 31.59m/s. where it shows a lot of variant in data because of the change of wind speed
which attack the wind turbines blades,
Table 4.4: Lift and drag force at different angle of attack at wind speed 31.59 m/s
From the graphs which has shown in Figure 4.10 it explains that the maximum lift force created at -10°
which is 1.01N and the minimum lift force 0.60N at 30°. Maximum drag force recorded 0.03N at -10° and
minimum is 0.02N at -5°.
Figure 4.10: Lift and drag vs angle of attack at 31.59m/s Figure 4.11 Lift and drag ratio vs angel of attack
at 31.59m/s.

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The maximum lift and drag ratio recorded in Figure 4.11 is 47.5 at -5°and minimum 30 at -30°. The ratio is
getting higher and proportional to wind velocity. Because of reducing the drag force at different angle the
graph shows a sinusoidal line otherwise it could behave like a straight line as there are linear changes of
data.
The Table 5.9 shows the tabulated the lift and drag force at different angle of attack at wind speed 36.47m/s.
pitching moment and L/D also collected to show the aerodynamic characteristic of the FHAWT blades.
Table 4.5: Lift and drag force at different angle of attack at wind speed 36.47m/s
From the graphs which has shown in Figure 4.10 it indicates that the maximum lift force created at -10°
which is 1.17N and the minimum lift force 0.71N at 30°. Maximum drag force recorded 0.05N at 15° and
minimum is 0.03N at -5°. The maximum lift and drag ratio recorded in Figure 4.11 is 35.3 at -5°and
minimum 17.6 at 5°. The ratio is high between -10° to 10°. The ration suddenly dropped at 5° which was
really unexpected.
Figure 4.10: Lift and drag vs angle of attack at s36.49m/s Figure 4.11 Lift and drag ratio vs angel of attack
at 36.49m/s.
4.3.2 Calculation to Find CL and CD
From lift force CL and CD can be found by using Equation 1 and 2 can rewrite the equation as follows
L = ½ CL ρ v2 A , CL= ……………… (3)
And, D =½CD ρ v2 A ,CD= …………… (4)
Now when,
Air foil section of the blade, r= 2.48 10-4 m, L = lifting force (N) = 1.2N (from experimental data)
D = drag force (N) =0.04 (from experimental data), ρ = density of fluid (kg/m3) = 1.225 kg/m3
v = flow velocity (m/s) =36.49 m/s,
A = body area (m2) =πr2 = (2.48 10-4 )2= 2.48 10-4 m2
CD = drag coefficient, CL = lifting coefficient

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Then, CL= = =1.8 And CD= = = =0.06
The calculated data has tabulated below:
Table 4.6: Calculated CL and CD at different angle of attack.
No
Angle of attack
(°)
Lift (N)
Drag (N)
CL
CD
1
-10
1.17
0.04
1.8
0.06
2
-5
1.06
0.03
1.61
0.04
3
0
0.98
0.04
1.50
0.06
4
5
0.88
0.05
1.38
0.08
5
10
1.01
0.04
1.58
0.06
6
15
0.86
0.05
1.25
0.08
7
25
0.77
0.04
1.15
0.06
8
30
0.71
0.04
1.05
0.06
4.4 Error calculation and Analysis
To see the errors between simulation and collected experimental data the error calculation has been done
with the help of theoretical data which has been obtained in section 4.3.1. the calculation has shown below:
Coming to the error analysis among the theoretical, simulation result and wind tunnel testing, it has seen that
the error between theoretical and simulation result for lift is around 9.37% and for drag is 10.71%. The data
seems very close to each other because in order to validate the result simulation and theoretical calculation
has performed. Both process includes mathematical problem and solved by equation. Both process use same
method. The difference for theoretical calculated by human and simulation performed by software. That’s
why the results are very close. On the other hand, the error between theoretical and wind tunnel test result
at 36.49 m/s for lift is around 14.6% and drag is 28.57%.
It shows a big difference between the result. The error may have occurred during performing the experiment
in the Thermofluids lab in UOW Malaysia KDU University College, Utropolis Glenmarie campus. This
error can happen mainly for three reason firstly instrumental error like loose pitot connection, measurement
error or the working chamber did not seal properly, secondly environmental error pressure loss between inlet
and outlet of wind tunnel while taking reading and the final reason is human error like doing some error be
human while doing the testing. The errors have shown to validate the data and the difference. This data is
acceptable and seen a slightly difference after comparison in this case.

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4.5 Performance analysis between twisted and untwisted blade
4.5.1 Existing untwisted wind turbine blades data
An untwisted wind turbine blade investigation has done in 2015 where it the analysis has carried out in
different angle of attack to find out CL and CD. In Figure 4.12 it shows the graphs had been plotted for two
different result one is CFD simulation and another one is for Sandia National Laboratory(SANDLA)
experimental result [8].
Figure 4.12: CL and CD vs. angle of attack [8]
In 2015 an untwisted air foil based wind turbine blades optimization has done to maximize the L/D ratio.
Where they used wind tunnel testing and CFD simulation to analyze it. In Figure 4.13and 4.14 the final
result from the investigation has shown where WT180 air foil has been used [9].
Figure 4.13: CL and CD vs. angle of attack [9]
Figure 4.14: CL and CD vs. angle of attack with Re.[10] (Chen et al., 2015)

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4.5.2 Designed twisted blade data for FHAWT
The graphs in Figure 4.15 and 4.16 represents the data from Table 4.6 where that graphs have plotted CL vs
Angle of Attack to do the comparison between existing untwisted blade and designed FHAWT twisted
blade.
Figure 4.15: CL vs Angle of Attack of designed twisted blades. Figure 4.16:CL vs Angle of Attack of
designed twisted blades.
From Figure 4.15 & 4.16 it has seen that maximum CL can get 1.8 at -10° and maximum CD which is 0.06
at -10° as well. The value of CL become lower after 20° and CD started to increase.
4.5.3 Comparison between twisted and untwisted blade
Now coming to the comparison part for untwisted blade two researcher’s data has been taken to compare
with designed twisted blade data.
At first if notice in Figure 4.12 [8] it can see that the maximum CL can get for the untwisted blade is around
1.05 and maximum drag is around 1.8 and on the other hand, the maximum drag is around 0.6 at 0° to 30°
angle of attack. Where twisted blade gives the highest CL is 1.8 and for CD is 0.06 and the lift and ratio will
be higher than the untwisted blade. And minimum CL is around 1.01 where the minimum CD is around 0.04
which occurs between -10° to 30° angle of attack.
Figure 4.13 and 4.15 [10] shows that maximum CL and CD between -10° to 20° is 1.14 and 0.17 where the
minimum is 0.1 and 0.01. Here the researcher [10] used WT180 which is known as Rfoil [11] though it is
good for wind turbine blade but because it is an untwisted blade that’s why gives high drag than the
designed FHAWT’s twisted blade. CL and CD is directly proportional to lift and drag force so the L/D ratio
depends on it [12]. Here it has been clearly seen that the L/D ratio for a twisted blade will be higher because
of low CD and high CL than untwisted blade.
For a twisted blades of a wind turbine the main magical thing happened is at drag because of in twisted
blade the wind can pass easily to reduce the drag force. It has seen that for the twisting angle the drag is
reduced almost 10 times than an untwisted blade. So it is clear that twisted blade give better performance
than an untwisted blade by reducing drag and increasing lift and drag ratio. Finally, can come to an opinion
that twisted blades aerodynamic performances are better than an untwisted blades wind turbine.
4.6 Performance of the twisted FHAWT blade
To see the performance of the designed twisted FHAWT blade need to see the performance of the prototype
of FHAWT which has been fabricated after analysing and get the optimization. The offshore environment
has been made in the laboratory by using a small swimming pool and industrial fan to give the wind 5m/s to

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8m/s. Then all the data has been collected to see the performance. The FHAWT was fabricated in 1/150th
Scale to see the performance. Table 4.7: Performance table of twisted FHAWT.
No
Parameter
Required /Generated
1
Weight of the blade
105.30 g
2
Weight of the FHAWT
1100g
3
Wind velocity
6.5-8 m/s
4
Distance from wind source
662 mm
5
Time to generate electricity
60- 90 s
6
Generated current
0.97 A
7
Generated voltage
0.9V
8
Generated power
0.93W
From Table 4.7 it represents that in 1/150th Scale the performance is quite satisfied. Where targeted shows
that the generated power supposed to be 1.01W where the fabricated FHAWT output power found 0.93W
which is very close to 1.01W where the difference is around 8%. So it can be stated that the twisted blade
will give the maximum power output based on high L/D ratio. Where to obtained high lift and drag force
ratio is the main focus of this project. Another thing to get more efficient power the required system
components can be added.
CONCLUSION
Finally, it can be concluded that the optimization of the FHAWT blades has achieved which shows high lift
and drag ratio than an untwisted blade. Although the FHAWT twisted blade was designed for the variable
speed operation in offshore environment it can be applicable for constant speed operation as well.
Therefore, velocity is directly proportional to lift and drag where high velocity increases the lift force to spin
the blade. Lift and drag ratio increased because twist distribution of the blade by using NACA6409 airfoil.
The main difference has observed in twisted blade than untwisted blade is drag where because of twisted
blade it reduced almost 10 times. It can be concluded that lift force and co-efficient highly increased when
the wind attacks to the blades between -10° to 20°. The lift gets higher most at -10° and 10° angle of attack
because the wind can attack directly at the edge of twisted blade to generate the lift force. The best place in
offshore to capture the energy should be investigating to reduce the waste of energy. An evaluation of rotor,
hub and nacelle should be done to optimize the FHAWT at different angle of attack and wind speed.
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