FABRICATION OF VERTICAL AXIS WIND TURBINE WITH WIND REDUCER AND EXPERIMENTAL INVESTIGATIONS

Transcription

1 87 CHAPTER-4 FABRICATION OF VERTICAL AXIS WIND TURBINE WITH WIND REDUCER AND EXPERIMENTAL INVESTIGATIONS

2 88 CHAPTER-4 FABRICATION OF VERTICAL AXIS WIND TURBINE WITH WIND REDUCER AND EXPERIMENTAL INVESTIGATIONS S. No. Name of the Sub Title Page No. 4.0 Introduction Problem formulation Modified moving blade VAWT designs Design of VAWT (single moving blade) model - I Design of VAWT (multi moving blade) model -I I 4.3 Experimental setup and its description Instruments used in the investigation Rotating disc type anemometer Non - contact tachometer Experimental procedure Determining experimental power coefficient Summary and conclusions 114

3 89 CHAPTER 4 FABRICATION OF VERTICAL AXIS WIND TURBINE WITH WIND REDUCER AND EXPERIMENTAL INVESTIGATIONS 4.0 INTRODUCTION The main objective of the present study is to increase the efficiency of vertical axis wind turbine using wind reducer system. The steps involved i n t h e m a n u f a c t u r e o f w i n d reducer, moving blades arrangement system and parameters of research are discussed in this chapter. The method of conducting an investigation in various stages using wind reducer system is also discussed in this chapter. Experimental setup consisting of wind reducer and model wind turbine are demonstrated. This chapter also includes the specifications of instruments like Anemometer, Non- contacting tachometer. The method used in finding the theoretical and experimental power coefficients of wind turbine in each module of the experiment, velocity gain by air, etc. are also presented. 4.1 PROBLEM FORMULATION The investigation is focused on enhancing the power coefficient. The effect of various wind reducers on power coefficient of wind turbine is discussed in the thesis. The wind reducer set is fabricated and fitted at topside and bottom side of the vertical axis wind turbine rotor. The wind reducers is fabricated as per dimensions of 3 meter of diameter each and angle of slope has been

4 90 taken as from 10 0 to 40 0 If the angle of wind reducer increases, the wind velocity al so i ncrease s up to 30 0 and further the angle increases then the velocity decreases, more inclination will act as obstruction. For a 30 0 slope, wind velocities were recorded at various heights. Simultaneously, measurements of the velocities were made at equal heights on plain surface. A micro-mini vane anemometer was used for wind power measurements. After fabrication of the wind reducer system, importance is given to vary the angle of reducer. Details of the experimental results and theoretical explanation are presented. The simplicity and economic viability of the method is expected to be a boon in converting poor windy sites to usable ones and to harness more energy at the existing wind mill sites. Theoretically and experimentally the power coefficient is determined under various stages of the experiment using wind reducer system. Only, by knowing the wind velocity at the middle of the turbine blade, the theoretical and experimental power coefficient of the turbine is compared in various stages of investigation at different angles of wind reducer. Wind mill rotor shaft rotates at different speeds, hence variation in speed studied in various stages of the experiment. The results show that wind speed increases with reducer with 1.2 times at the top of the reducer. The maximum increase is noticeable at about 30 0 slopes. Therefore I constructed typical wind mill about 3 meter height, 30 0 slope and 3 meter length since the power is increased by times as power is cube of velocity.

5 91 In general, the value of wind speed mentioned in meteorological data is taken height about 12.2 meters and this is taken into consideration while calculating the possible wind power that may be tapped. To know the real gain in field, wind speed has to be found with respect to the above value. The calculated values are plotted along with a wind profile over a plain turbine. From the graph it can be seen that the maximum gain is about 1.2and hence the power (1.2) 3 = To find an answer for frequent directional changes in wind, further experiments were carried out a curved (concave shaped) 30 0 model and symmetrical triangular 30 0 model. In the curved model wind velocities were measured at the extreme ends and the middle, the increase was found to be almost same (about 1.2 times) at about half of the height. The triangular model gave an increase in wind speed of about 1.1 times at half of the height. These results show that in coastal areas where wind direction changes in the day and night, symmetrical 30 0 wind reducer can be utilized. In areas where frequent changes in wind direction occur, curved wind reducer will be useful. The latter experimental results may be useful to increase wind speed at the existing windmill sites. In a bid to find a cheap material to make sloping structures and which are mobil, for which glass reinforced plastic has been chosen. Glass reinforced plastic wind reducer will help to give smoothness and prevent it from rain and corrosion. In choosing glass reinforced plastic for the sloping structure the following advantages were taken into consideration. Glass reinforced plastic is

6 92 abundantly available in any developing countries. Some studies by researchers reveal that glass reinforced plastic have been found to have half the yield strength of mild steel. It also cheap, corrosion resistance and light in weight. It was found that reinforced plastic slabs can be designed like steel reinforced concrete, taking permissible tensile strength and bond strength as 24,000 KN/M 2 and 350 KN/ M 2 respectively. Glass reinforced plastics have low strength but its cost is very cheap. Therefore Glass reinforced plastics are preferable. Fig: 4.1 Upper Cone (Reducer) Fig: 4.2 Dimensions of Cone (Reducer)

7 93 Fig: 4.3 Blade Fig: 4.4 Dimensions of Blade Fig: 4.5 Wind Mill Shaft Fig.4.6 RPM reading of wind mill Fig: 4.7 Wind mill assemble

8 94 Fig: 4.8 Measuring of wind velocity Computational fluid dynamics is used for the validation of air velocities from moving blade system. Computationally and experimentally air velocities from moving blade systems are determined and compared. Variations in fluid properties like pressure, turbulent kinetic energy, etc, along the length of moving blade system are also studied using CFD. Two more vertical axis wind turbines are also designed with moving blades arrangement system for improving efficiency. Fig: 4.9 Shows that the drag force on different objects [167]. Fig: 4.9 Drag force on different objects (Source: Muller, Air craft performance analysis, 2009)

9 MODIFIED MOVING BLADE VAWT DESIGNS The main drawback of Savonius is its low efficiency; this is due to the opposing force of opposing blade with the free stream. Fig: 4.10 Schematic view of Savonius rotor This can be briefly explained by some simple calculations given below Moving Blade Design of VAWT a. Radius of the rotor (R) b. Number of blades (B) c. Tip speed ratio of the rotor at the design point (λ) d. Angle of attack of the airfoil (α) e. Material of mild steel 1. Blade 2. Shaft and 3. Support Dimensions of VAWT Fig: 4.11 Savonius VAWT with moving blades

10 96 1. The rotor diameter (D) is1000 mm and the diameter of centre shaft is 80 mm. 2. The two end-plates have been made from 40 mm thick steel sheets with 1250 mm diameter 3. The overlap distance between fixed blade and moving blade (d) = 20 mm.

11 Design of VAWT (single moving blade) Model - I This is another method of moving blade arrangement system without changing the basic structure of a Savonius wind rotor to improve the performance and increase the efficiency of the rotor. In this study, a single moving blade arrangement is used. Model calculations of VAWT: [169] is given by the formulae P = C D 2 1 Power generated by the drag force 2 V W VR AVR (4.1) Where: V W is wind velocity, ρ is air density A is area of the rotor and V R is rotor velocity. C D on semicircular concave surface and semicircular convex surface are 2.3 and 1.2 respectively. Hence, Power generated by the drag force on concave surface, Pconcave=2.3 * V W VR AVR (4.2) Power generated by the drag force on convex surface, P convex=1.2 * V W VR AVR (4.3) Since the drag force on the convex side is opposing the concave side, net power generated from the Savonius rotor is P= P concave - P convex= 1.1 * V W VR AVR (4.4) This net power generated is low. Suitable modifications to the VAWT design are needed in order to increase the efficiency of VAWT. Hence, we introduce a moving blade arrangement without changing

12 98 the basic structure of a Savonius wind rotor to improve the performance and increase the efficiency of the rotor. Construction of modified Savonius VAWT. Fig: Modified (single moving blade) VAWT. This modified Savonius wind turbine consists of one moving blade on each side of rotor (convex and concave). The arrangements of moving blades are shown in the figure The original position of moving blade is shown as the moving blade in closed position in the above figure. The moving blades are designed such that they have a provision to move through 90 degrees in clock wise direction and return to its original position when required.

13 99 Working of modified Savonius wind turbine: Fig: VAWT at zero degrees of rotation Let us consider that the VAWT consists of two moving blades (blade A on concave side and blade B on convex side) as shown in the above figure. Fig: Rack and pinion arrangement The moving blades can rotate through 90 0 by moving the pinion gear attached to moving blade as shown in figure The pinion gear is driven by the rack which in turn driven by the connecting rod. When the VAWT is rotated to 180 degrees, the moving blade B will rotate through 90 degrees in clockwise direction and the moving blade

14 100 A will rotate through 90 degrees in anticlockwise direction. Now the position of VAWT will be as shown in next page. When the VAWT is again rotated to 180 degrees, the moving blade A will rotate through 90 degrees in clockwise direction and the moving blade B will rotate through 90 degrees in anticlockwise direction and this is a cyclic process. Fig: VAWT at 180 degrees of rotation From the above calculations, it is derived that movable blade design has better efficiency than the existing fixed blade design. Hence, theoretically, Cp of VAWT with moving blades design will be 29x1.818 = (Cp of conventional VAWT is considered as 29) From the above calculations I found that movable blade design is more efficient, in that movable blade design I assumed two different shapes of blades (airfoils).

15 101 a) Cambered Airfoil Here it is assumed to use a cambered air foils as movable blade Fig: 4.16 Cambered airfoil blade Then by using this type of airfoils the total shape of Savonius rotor will be: Fig: 4.17 Modified VAWT with cambered airfoils

16 102 b) Symmetrical Airfoil Here it is assumed to use a symmetrical air foils as movable blade Fig: 4.18 Symmetrical airfoil blade Then by using this type of airfoils the total shape of Savonius rotor will be: Fig: 4.19 Modified VAWT with symmetrical airfoil sections

17 Design of Vertical (multi moving blade) model-ii In design of VAWT the 1 st issue comes with design of Airfoils that can be place in Savonius turbine. Details of Airfoils for my model are as given below Chord = 184 mm Airfoil Thickness = 9% C Thickness location = 30% C Camber = 0% C Camber location = 40% C These values are taken by considering that the swept area of turbine is ~1sq.m. The design of turbine with above values is given as. By considering the above value into consideration the air foil is created in UniGraphics which is shown below Fig: 4.20 Symmetrical Airfoil Dimensions Fig: 4.21 Symmetrical Airfoil Modeled in UniGraphics

18 104 WIND Fig: 4.22 Complete Airfoil assembly dimensions As shown in above figure, each side (convex and concave) of rotor consists of 5 blades. Out of which only 2, 3 and 4 numbered airfoils are movable and 1 and 5 are fixed airfoils. These blades will rotate when the concave side of the rotor faces the wind to minimize the opposing force of rotor on wind as shown in above figure. In this blade 2 will rotate through 60 0, blade 3 will rotate through 95 0 in clockwise direction and blade 3 will rotate through 40 0 in anti-clockwise direction. These movements are shown below in the figure:

19 105 Fig: 4.23 Angle of Attack of different airfoils while running Fig: 4.24 Completed Turbine Assemblies with Airfoils

20 106 Fig: 4.25 Assembled model of Vertical Axis Wind Turbine 4.3 EXPERIMENTAL SETUP AND ITS DESCRIPTION Investigation requires a wind tunnel since it produces air at constant velocity. Complete description of wind tunnel, wind turbine, etc, are furnished in this section. Wind tunnel is used to supply air continuously at constant velocity. It is driven by a blower mounted at one end. Air is sucked at the other end called inlet duct. The equipment consists of convergent and divergent portions and, with a test section at throat. Wind tunnel is used to analyze the lift and drag forces on airfoil shaped blades of aero planes, wind turbine, rotary compressor, etc. The pressure developed on blades at

21 107 different positions can be determined using manometers. Wind tunnel is driven by D.C blower. Blower Specifications: Make : Kirloskar Electrical Company Limited Phase : Three phase induction motor Speed : 1400 RPM Voltage : 415 volts Current : 4.9 A Power : 2.2 kw Connection : Delta Size of the inlet duct: Length : 0.91 m; Width : 0.91 m Size of the test section: Length : 0.48 m Height : 0.29 m Width : 0.30 m Size of the outlet circular duct: Diameter : 0.6 m Total length of wind tunnel : 5.05 m Various portions of wind tunnel and their details are stated below. Inlet duct: It is aerodynamically contoured section with contraction area ratio 9:1. The square shaped duct has dimensions of 900 mm X 900 mm. For effective flow of air, the ratio of length to cell

22 108 size of the honeycomb is taken as 6, as per the recommendations of the vendor of wind tunnel. Further, the wire mesh smoothens the air flow. Provision is made to remove the screen for cleaning of wind tunnel. Also, higher velocities can be obtained if the screen is removed, but it is not of laminar. The duct is secured to the test section by bolts. The provision is made to separate test section and inlet duct. Test section: It is the center portion of the tunnel cram between the inlet duct and the diffuser. It has a transparent window, which facilitates visualization easy. The traversing mechanism is fixed on its top for the movement of pressure probe. There is a provision to calibrate strain gauge for determining lift and drag force. A few holes on all sides test section are made to keep airfoil model tight in the test section and pressure probes. 4.4 INSTRUMENTS USED IN THE INVESTIGATION Rotating disc type anemometer is used to determine air velocity. A Non contacting (Laser beam) tachometer is used to measure speed of turbine during power measurement Rotating Disc Type Anemometer Rotating disc type anemometer (MEXTECH AM-4204) is placed in the direction normal to the direction of air flow. Anemometer is shown in Figure The circular disc of anemometer rotates when it is placed in the direction of air flow. The number of rotations

23 109 made by the disc is calibrated into air velocity in m/s. Air velocity can also be measured in knots or Kilometers per hour using such anemometer. It works safely even in the range of m/s. A digital monitor is provided to indicate wind speed. Anemometer is calibrated in the range of 6 m/s to 29.5 m/s. Fig: 4.26 Rotating Disc Type Anemometer Fig: 4.27 Non Contact Tachometer Non - Contact Tachometer A Non-contacting tachometer is shown in Figure It is a device used to measure speed of the rotating shaft of turbine in revolutions per minute. It does not have any physical contact with rotating shaft. Such tachometer is best suited in wind farms since turbine is mounted at great heights. A light beam from source is focused on to a target marked on the rotating shaft. A photo receiver receives the reflected light beam with the help of photo probe. Both light source and photo

24 110 receiver are housed at front side of tachometer. The time interval between the two consecutive sensations is calibrated into R.P.M. A digital screen is provided to indicate speed of the rotating shaft. The instrument is calibrated in the range of 500 R.P.M to R.P.M. 4.5 EXPERIMENTAL PROCEDURE In various modules of experiments stated above, the power coefficient of wind turbine is determined at various wind reducer orientations. Power coefficient is determined theoretically and experimentally. The air at high speed from wind tunnel is focused on to rotor of the turbine. In these modules, the efficiency of the conventional model wind turbine is determined with and without using the wind reducer in conical shape with deferent angles, single moving blade and multi moving blade system at different positions of blade, finally a slope of deferent angles with two curtains arrangement has been considered to Savonius wind rotor to enhance the turbine rotor speed. For module M4 schematic diagram of the experimental set-up that has been used in this study is shown in Figure The Savonius wind rotor, slope with curtain arrangement and measurement devices have been installed away from the exit of this wind tunnel. The Savonius rotor and slope with curtain arrangement have been placed on a steel table. The Savonius rotor shaft has been supported near the top and bottom by a very low friction ball bearing to minimize the friction force. The curtain arrangements have been

25 111 placed in front of the Savonius wind rotor. And then measurements of rotor torque, wind velocity and the number of revolution have been measured by a torque meter sensor, multifunctional anemometer and a tachometer. Dimensions of curtain arrangements are 135cm. and 156cm. and the angle of slope is Fig: 4.28 Schematic view of rotor with and without slope and curtain The vertical shaft of the wind turbine rotates Initially, the rotor is allowed to rotate without freely in bearings. connecting reducer. Power coefficient is determined theoretically by knowing wind speed at the inlet of wind turbine. Later, experimental power coefficient is determined when the turbine is fixed with wind reducer arrangement. Rotating disc anemometer is placed in a direction normal to

26 112 the flow of air to determine air velocity at the inlet and outlet of the wind turbine. Theoretical power coefficient, which is the ratio of theoretical power to power in the wind, is determined in various modules. In module M1, under the first change in the experiment, the fabricated wind reducer is assembled to wind turbine. The high velocity of air rotates the rotor of turbine at high speeds. Theoretical power coefficient is determined at different angle of wind reducer. As part of the next evolution in conducting the investigation i.e, under module M2, moving blades system is joined to wind tunnel. The moving blade system produces air at a high speed and kinetic energy due to increased coefficient of discharge. The theoretical power coefficient is then, determined. To study the effect of the 3 r d method of better wind energy conversion into kinetic energy by aerofoil moving blade used in conducting the investigation i.e, under module M3, moving blades system is joined to wind tunnel. The moving blade system produces air at a high speed and kinetic energy due to increased coefficient of discharge. The theoretical power coefficient is then, determine. The change in revision is named as module M3, and the theoretical power coefficient is determined. The curtain and slopes system produces air at a high speed and kinetic energy due to increased coefficient of discharge.

27 113 Fig: 4.29 Geometrical parameters of rotor with slope and curtain Fig: 4.30 Schematic view of experimental setup

28 114 In all the modules of experiments, wind turbine is placed at same distance from wind tunnel Determining Experimental Power Coefficient The d yna mo i s connected to produce D.C current and t he n t he experimental power coefficient of wind turbine becomes the ratio of power produced to the power available in the wind. It is determined in all stages of the experiment as discussed above. All instruments are calibrated in recording the data. 4.6 SUMMARY AND CONCLUSIONS The problem is formulated based on determining experimental and theoretical power coefficients of the wind turbine. Under research methodology, various modules of experiment are discussed. Various instruments like rotating disc type anemometer, non-contacting tachometer etc, are demonstrated. The research methodology in carrying out the investigation is also discussed. After the conduct of the experiment, the results are discussed in chapter 7.