EFFECT OF VERTICAL MOVEMENT IN HAWT

It is known that to work properly, the horizontal-axis turbine needs the wind to flow at a right angle to the blades. If it blows from a different direction than the blades are facing, the turbine gets much less energy from the wind. To accommodate changes in wind direction, the turbine has a yaw drive that rotates the unit’s direction. By contrast, a vertical turbine runs well regardless of wind direction, making it better-suited to urban areas with tall buildings where wind turbulence is a given. The vertical-axis design allows it to operate on lower wind speeds than is possible with the horizontal turbine. So, this paper focusses on the pitch movement as well as the nacelle and tower movement of the turbine in three dimensions with respect to the ground as the wind should be at right angle to the blade of the turbine or the attack of angle to the blades should be 0 ₒ . This paper analyses if the increase in efficiency of the HAWT turbine due to the pitch movement is significant as well as the cost set up for the vertical movement is reasonable with the increase in efficiency (i.e., power increment ultimately leads to the profit increment). For this NACA0012 aerofoil was chosen as the wind

It is known that to work properly, the horizontal-axis turbine needs the wind to flow at a right angle to the blades. If it blows from a different direction than the blades are facing, the turbine gets much less energy from the wind. To accommodate changes in wind direction, the turbine has a yaw drive that rotates the unit's direction. By contrast, a vertical turbine runs well regardless of wind direction, making it better-suited to urban areas with tall buildings where wind turbulence is a given. The vertical-axis design allows it to operate on lower wind speeds than is possible with the horizontal turbine. So, this paper focusses on the pitch movement as well as the nacelle and tower movement of the turbine in three dimensions with respect to the ground as the wind should be at right angle to the blade of the turbine or the attack of angle to the blades should be 0 ₒ . This paper analyses if the increase in efficiency of the HAWT turbine due to the pitch movement is significant as well as the cost set up for the vertical movement is reasonable with the increase in efficiency (i.e., power increment ultimately leads to the profit increment). For this NACA0012 aerofoil was chosen as the wind turbine blade in this blade. Since, it is well known as DU, FX and NACA-63 and NACA-64 series aerofoils are commonly used for the blades of HAWT turbine. The aerofoil was simulated using ANSYS 15 software at assumed 10 m/s wind velocity for the attack angles 0 0 , 15 0 and 30 0 and analysis of power difference is to be analysed.

Introduction:-
As the world continues to use up non-renewable energy resources, wind energy will continue to gain popularity. A new market in wind energy technology has emerged that has the means of efficiently transforming the energy available in the wind to a usable form of energy, such as electricity.
The cornerstone of this new technology is the wind turbine. A wind turbine is a type of turbo machine that transfers fluid energy to mechanical energy using blades and a shaft and converts that form of energy to electricity using a generator.
Wind turbines have two main design categories: HAWT and VAWT. The horizontal-axis turbine typically has a three-blade vertical propeller that catches the wind face-on. The vertical turbine has a set of blades that spins around a vertical axis. Each has its own merits and demerits.

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Horizontal-axis turbines convert more of the wind's energy into useful mechanical motion if the blades are perpendicular to wind direction, and then the blades would pick up the maximum energy throughout their range of movement. By comparison, the blades on a vertical-axis turbine suffer an efficiency disadvantage, capturing energy from the wind only on the front side; at the rear part of their rotation, they drag on the system. Same goes for VAWT. If the VAWT is at an angle to the wind direction the power output will get affected (output power is reduced).
Since, HAWT requires a yaw mechanism to adjust to changing wind direction, the horizontal-axis turbine is mechanically more complex than the vertical design.
The HAWT is optimum at the tall towers as long blades work well only in wide-open spaces. VAWT are generally much more compact and can be placed on building rooftops and other urban locations with fewer restrictions. The vertical unit's low height also makes it suitable for areas where wind picks up speed between buildings or over hilltops.

Used for Aerofoil Analysis: General Idea for Power Calculation of Turbine
The efficiency of the wind turbine depends on the area swept by the blades as well as the wind velocity perpendicular to the area swept by the blades.If the nacelle is not parallel to the ground. The area will not be perpendicular to the wind and will be at an angle (say x).The area will become (A cosx) therefore, the power will reduce.

Governing Equations:
The continuity equation for the two dimensional, steady and incompressible flow is:

Theoretical Analysis of Wind Turbine:
1. If the angle of attack changes, the velocity which is useful to the turbine will also change. The velocity perpendicular to the cross section will now become V cos(x). 2. Since, the velocity is cubed for power calculations for wind turbine then this will reduce the power output significantly. 3. Let for x= 30˚, cos(x)=0.8660. Therefore new V 3 =(0.6495) V 3 (old velocity) as well as new area A=(0.8660)A (old area). 4. Then the new power obtained will P new = (1-(cos(30)) 4 )P old P new = 0.5625 P old Then, reduction or loss in power generation is: 1008 ΔP = P old -P new ΔP = (1-0.5625) P old ΔP = 0.4375 P old Then, there is 43.75% in power reduction which cannot be neglected.

Geometry and Simulation:
NACA0012 was taken into consideration for 1 m length was solved in ANSYS 15 fluent. The governing equation for the aerofoil or the formula for the shape of a NACA 00xx foil, with "x" being replaced by the percentage of thickness to chord, is: where: x is the position along the chord from 0 to 1.00, (0 to 100%) 2. y t is the half thickness at a given value of x (centerline to surface), and 3. t is the maximum thickness as a fraction of the chord (so t gives the last two digits in the NACA 4-digit denomination divided by 100).
Note that in this equation, at (x/c) = 1 (the trailing edge of the airfoil), the thickness is not quite zero. If a zerothickness trailing edge is required, for example for computational work, one of the coefficients should be modified such that they sum to zero. Modifying the last coefficient (i.e. to −0.1036) will result in the smallest change to the overall shape of the airfoil. The leading edge approximates a cylinder with a radius of: r = 1.1019 (t 2 /c) The geometry was created by importing the coordinates file into the ANSYS software and meshing was using the edge sizing and inflation method in which number of layers were given the value of 15 and Growth rate as 0.05. For this case, left, top and bottom surface of the bigger geometry were considered as inlet, right boundary was considered as outlet and the region excluding the aerofoil body was considered as wall.

Velocity (Tangential and Radial) Contours:
Like the aforesaid velocity magnitude contours, these figure depicts the tangential and radial velocity magnitude for each of the attack angles specified below. It is found to assume the wind velocity as for the above one and also to observe the uniformity of velocity distribution through the blades when passed through it as uneven velocity magnitude may create uneven dynamic pressure which may damage the blades.  1016

Cost Calculations: Cost required for motor installation:
Since, it is given that for 1.5 MW turbine that mass of the nacelle is around 56000 kg if mass of the blade assembly is 36000 kg. Then the total mass of the assembly system will be 92000 kg. It is also known that length of the blades is about 36 m having mass of about 11000 kg if the blade assembly is 36000 kg.
Then the mass % of the other parts of blade and blades will be: % M others = (3000/36000)×100 = 8.33. % M blade = (33000/36000)×100 = 91.67. Then, for our case let us assume the blade assembly be: Cost difference in power generation due to the attack angles: Let the C p (Coefficient of Performance) of the wind be around 0.4 and density of air be taken as 1.225 kg/m 3 for all cases as for India C p is around 0.35 -0.45.

For 0˚:
In this case, for pressure contour inferring that the maximum pressure of about 60.7 bar is applied at the tip of the blade which is negligible. On a range of (0.2-4) bar was seen around the blade.
From the velocity magnitude contour, we infer that the whole region is around the speed range of (10.01 -11.8) m/s. Tangential and radial contours confirms the assumption as for the tangential contour maximum region indicating a velocity of 10.2 m/s was seen at the perpendicular to the tip of the blade whereas for radial contour, regions of 9.22 to 11.4 m/s was seen along the geometry of the blade. These above conclusions indicate that the velocity of 10 m/s should be reasonable to use for our calculations i.e. V = 10 m/s. In this case, for pressure contour inferring maximum pressure of 62.8 bar is acting over a reasonable area of blade tip and an unbalanced region of pressure ranging from (0.7 -62. 8 bar) around the blade geometry.
From the velocity magnitude contour we can observe that around the three regions were seen i.e., (9.79 -10), (5.25 -9.79), (0.7 -3.77) m/s. A small region of (11.28 -11.51) m/s was around the blade. Tangential and radial contours indicates the distortion of the region over the blade geometry. So for this case velocity of 9.2 m/s would be reasonable to choose as it is not according to the theoretical assumption since the region is divided into too many velocity regions. Therefore, V= 9.2 m/s. In this case, for pressure contour inferring maximum pressure of 61.5 bar is acting over a more area of blade tip than the previous case and an unbalanced region increased of pressure ranging from (0.84 -61. 5 bar) around the blade geometry. The regions are completely randomized and distorted indicating the blades are exposed to unbalanced pressure.
From the velocity magnitude contour we can observe that velocity regions of lower magnitude are observed around the blade mainly (5.77 -9.9), (0.825 -4.12) and a small region of (11.77 -16.5) m/s was observed that the blade is exposed to uneven velocity magnitude which may cause turbulence around the blade the region. Tangential and radial indicates the same thing as the regions are more distorted from the previous one which doesn't seem to supportive for the blade movement. So for this case keeping in accordance with the theoretical value velocity of 8.1 m/s would be reasonable to choose i.e., V = 8.3 m/s. It should be noted that the contours for 30˚ is not reliable as the solution didn't converged after 2500 iterations as well as 30˚ of attack angle difference is unrealistic in physical applications as it is assumed that wind turbine blades are not exposed to 30˚ of attack angle.
Then the power difference due to change in attack angles i.e., (P 0 and P 15 ) is given as: ΔP = P 0 -P 15 ΔP = (692.