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Performance Evaluation of Co-Axis Counter-Rotation Wind Turbine
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 79 (2015) 149 – 156
2015 International Conference on Alternative Energy in Developing Countries and Emerging Economies
Performance Evaluation of Co-Axis Counter-Rotation Wind Turbine Tanate Chaichanaa*, Sumpun Chaitepb b
a School of Renewable Energy, Maejo University, Chiang Mai, Thailand Retired, Department of Mechanical, Faculty of Engineering, Chiang Mai University, Thailand
Abstract The present work was studied the effect of the tip speed ratio to the starting rotation, rev up rotation, power and torque coefficients of a two-shaft co-axis counter-rotating wind turbine (CR-WT). The prototype of CR-WT was tested in the open type wind tunnel with the velocities of 1.5, 2.0, 3.0, 4.0 and 5.0 m/s. CR-WT consisted of 8 blades. The blade is made of wood. It consists of 2 hubs 2 axis and 4 arms. The inner axis is clockwise rotation and outer axis is anticlockwise rotation. The inner and outer are in the identical axis. Both axes are driven the pulley by using the counter rotating gear. The analysis of the experimental results showed that the cut in wind speed of CR-WT was 1.744 m/s and it is increasing when the tangential force ratio increasing. Rev up rotation period depends on wind speed and tangential force ratio. The average of power coefficient of CR-WT was 14.89%. © 2015 Authors. Published by Elsevier This is Ltd. an open access article under the CC BY-NC-ND license © 2015The The Authors. Published byLtd. Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE. Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE
Keywords: Vertical Axis Wind Turbine, Power Coefficient, Cut-in Wind Speed, Tip Speed Ratio
1. Introduction Wind is a natural resource and it can use as an alternative energy. Wind energy is a one of the better choices to compensate fossil energy and solve a problem about the energy situation in Thailand. Other Moreover, wind energy is clean, abundant and it can reduce the global warming problem. There are 2 kinds of wind in Thailand [1], seasonal and local wind. The seasonal (monsoon) wind is consisting of north-eastern wind and south-west wind. Local wind is a wind system that's expected change in direction every such as mountain-valley breezes, land-sea breezes. Wind power is the conversion of wind energy into a useful form, such as electricity with wind turbines. Generally, wind turbines can be divided into two types based on the axis in which the turbine rotates. There are horizontal axis wind turbine (HAWT) and Vertical-axis wind turbines (VAWT), but
*
1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE doi:10.1016/j.egypro.2015.11.453
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
HAWT is more popular than the other one. VAWT have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. VAWT can work in all directions and it requires low wind speed (2 m/s) [2]. However, the VAWT has lover rotational speed and efficiency than HAWT in which a maximum tip speed is not over double of wind speed and 1 7 – % 3 0 of efficiency [3]. Nevertheless, the efficiency of VAWT will be increased by adding some equipment, such as Savonius type of main turbine, resulting in the cut in wind speed is reduced [4]. Nomenclature U
Air density (kg/m2)
A
Swept area of the wind turbine (m2)
V
Wind speed (m/s)
F
Tangential force (N)
N
Rotational speed of turbine (RPM)
r
turbine radian (m)
்ܲ
Mechanical power (Turbine Power) (W)
ܲ௪
Wind Power (W)
ܥ
Power coefficient (dimensional less)
ܥொ
Torque coefficient (dimensional less)
ܸ௨௧ି Cut in wind speed (m/s), the minimum wind speed at which the turbine first starts to rotate. XF
The divided tangential force at pulley by swept area of the wind turbine (N/m2)
ܶ௦
Time from turbine first starts rotated to a constant rotational speed (s)
ܰ
The rated rotational speed (RPM)
The development of the vertical axis wind turbine has been explored over 30 years [5-8]. Recently, the vertical axis wind turbines are more on attentiveness in term of optimization of power generation and cost effective. Ever since 1925 – 1926, the initial result was shown the various experimental work out how they design [9]. However, the Horizontal Axis Wind Turbines (HAWT) is still the favourite configuration of turbine for electrical generation. Many types of rotor have designed and tested for evaluating the behaviour and efficiency. Additional of Savonius to Darrieus type vertical wind turbine can increase the efficiency and decreased the wind speeds essentially required for starting rotation [10]. The present work studied the effect of the operating conditions to the starting rotation, rev up rotation, power and torque coefficients of a two-shaft co-axis counter-rotating wind turbine (CR-VAWT). 2. Performance Analysis The total power of the wind stream is proportional to the air density, cross section area of the swept frontal of the wind turbine perpendicular to the air flow, and the wind speed. Of which can be written as, ܲ௪ ൌ ͲǤͷߩ ܸܣଷ
(1)
The mechanical power (்ܲ ) produced by the wind turbine is a functions of tangential force and rotational speed of axis and is equal to
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
்ܲ ൌ ʹߨܰܨݎȀͲ
(2)
The power coefficient (ܥ ) of a wind turbine is explained as the mechanical power output from that turbine divided by the total power accessible in the cross-section area of the wind stream input to the wind turbine. i.e.,
ܥ ൌ ்ܲ Τܲ௪ ൌ ሾʹߨܰܨݎȀͲሿȀሾͲǤͷߩ ܸܣଷ ሿ
(3)
The torque coefficient (ܥொ ) is analysis by the defined as the dividing of power coefficient of a wind turbine by the tip speed ratio (O) of the turbine. ܥொ ൌ ܥ ΤO
(4)
3. The experiment setup Two-shaft co-axis counter-rotating wind turbine (CR-VAWT) consisted of 2 rotors 4 wood blades per rotor. The model of the blade has a shape of hollowed semi-cylinder 300 mm height, 150 mm width and 1 mm of thickness. Both ends of the curved blade are attached with semi-circular plates of similar thickness. Diameter of both rotors is 150mm and swept is 0.045 m2. The inner axis is clockwise rotated and outer axis is anticlockwise rotated. Inner and outer axes are in the identical axis and have a same axis rotation. The counter rotating gear was used to connect 2 Inner and outer axis. Inner axis was connecting to pulley for measurement the power output. The component of CR-VAWT is shown in Fig. 1.
Upper Hub and Arm (76.2 mm diameter and 22 mm high 9.50 mm axis - hole diameter)
Counter rotating gear
Upper Hub Clockwise rotation
Counter clockwise rotation Lover Hub (76.2 mm diameter and 22 mm high 6.35 mm axis - hole diameter) Vertical column with 2 ball bearings
8 Curved Blades (150 mm high, 150 mm wide and 75 mm thickness).
Outer axis (6.35 mm diameter and 800 mm high) Inner axis (6.35 mm diameter and 1,000 mm high)
Pulley
Fig. 1 CR-VAWT Component
Lover Hub
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
To measure the power of the rotor, a pony brake principle is used. The difference between the dead weight and load cell readings producers the tangential force action on the pulley. Time and value were recorded and process by computer. The rotational speed was measured by a laser sensor tachometer. Wind speed in wind tunnel was control of fan with inverter and measure by a hot wire type anemometer. The testing methods were used in this research; blade pitch angle was fixing at 0o, dead weight rang 0-1 kg. Dead weight was added and corresponding rotational speed were recorded until the turbine cannot rotate by itself. The signal from load cell was amplify by electronic amplifier and recorded by an oscilloscope. The rotational speed, N, was measured by a laser type tachometer. Hot wire type anemometer was used for measuring the wind speed. The experiment setup is shown in Fig. 2.
Wind tunnel I 0.8 m. Fan
N Turbine Wind direction
0.45 m 1m
2m
Motor
Tachometer (Laser)
Anemometer (hot wire)
Load cell
Investor
T Dead weight
Wind direction Angle of attack (T)
RH meter Computer Oscilloscope
Amplifier N
Fig. 2 the experiment setup 4. Results and Discussion 4.1 Cut in speed The factor was effective to cut in wind speed of CR-VAWT is a tangential force acting the pulley or load (XF). Fig. 3 shows the variation of rotational speed of CR-VAWT with XF, the divided tangential force acting the pulley by cross section area of the swept of the wind turbine, N/m2, of the various setting wind speed of 1.5 – 4.0 m/s. Rotational speeds reach zero with a maximum value of the corresponding tangential force ratio. A rotational speed of CR-VAWT was becoming lower in curve line, but for nVAWT the rotational speeds were become lower in a straight line. The rotational speed of CR-VAWT was softly become lower when XF increase. It is a good property for keeping the mechanical system.
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156 5.0 4.5
Cut in speed (m/s)
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0
50.0
100.0
150.0
200.0
XF (N/sq-m)
Fig. 3 cut in wind speed of CR-VAWT The cut in wind speed increase when the XF increase and it became constant about 5.0 m/s. The cut in wind speed is a logarithm function of XF (N/m2) as expressed by equation 5 with the coefficient of determination (ܴଶ ) of 99.64% and with error 1.11%. Equation 5 shows that at no load the cut in wind speed were 1.74 m/s. It is the wind speed that can exert force to overcome all frictional losses of the CBVAWT. ܸ௨௧ି ൌ ሺͳǤʹͲሺ݈݊ܺܨሻሻ െ ͳǤͶ
(5)
When ܺ ܨൌ
୲ୟ୬ୣ୬୲୧ୟ୪୭୰ୡୣ୦ୣ୮୳୪୪ୣ୷ ୱ୵ୣ୮୲ୟ୰ୣୟ୭େି
ൌ
ሾିிೌ ሿ ோൈ௦
(6)
4.2 Rev up rotation The factor was effectively to rev up rotation, a phenomenon of that rotor accelerated from rest up to a constant rotational speed, which can be defined as a successful ‘start’, of Vertical Co-Axis CounterRotation Wind Turbine depends on wind speed and XF. Some researcher calls rev up rotation is a starting time sequence. At lower wind speeds the starting time sequence (ܶ௦ , s) go up more rapidly with respect to the increasing rate of XF. Conversely, at higher wind speed ܶ௦ go up with less responsive to the increasing rate of tangential force. Fig. 4 reveals the relationship between starting time sequence and XF at several of wind speeds. The relationship between starting time sequence (ܶ௦ ), XF and wind speed was explained by equation 7. The accuracy of this equation for prediction the starting time sequence is 95.62% correlation to the experimental data is shown by Fig. 4. Equation 7 cannot also be applied if both ܸ and XF are equivalent to zero. ܶ௦ ൌ ሺെͳǤͲͳሺ݈ܸ݊ሻ ͳǤͷͷሻܺ ܨ ͲǤͲͷܸ ଷǤଶ
(7)
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
V=2.0 m/s
30
V=3.0 m/s V=3.5 m/s
Starting time sequence (s)
25
V=4.0 m/s 20
V=4.5 m/s
15 10 5 0 0.0
20.0
40.0
60.0
80.0
100.0
XF (N/sq-m)
Fig. 4 Rev up rotation and ܺி of various wind speeds of CR-VAWT 4.3 Rated rotation The rated rotational speed was a direct variation with wind speed and inverse variation with tangential force. At any particular constant wind speed, the rated rotational speed decrease with the increase of tangential force ratio. On the other hand, at the constant of tangential force, the rated rotational speed was a direct variation with wind speed. Fig. 5 shows that the rotational speed of CR-VAWT with XF at deference value of wind speed. The relation of rated rotational speed, wind speed and tangential force is given by equation 8. The accuracy of equation 4 to predict the rated rotational speed is 96.59%. Equation 8 cannot also be applied if both ܸ and XF are equivalent to zero. ܰ ൌ ሺʹ͵Ǥͳʹሻܸ ሺെͲǤ͵ͳܺܨሻ ʹͷǤͲ
(8)
70.0
V=2.0 m/s V=3.0 m/s V=3.5 m/s V=4.0 m/s V=4.5 m/s
rated speed (RPM)
60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.0
50.0
100.0
150.0
200.0
XF (N/sq-m)
Figure 5 Rated rotational speed and ܺி of CR-VAWT 4.4 Power and Torque Coefficients Fig. 6 and 7 shows the power coefficient and the Torque coefficient of CR-VAWT at tip speed ratio. Power coefficient was increased to a maximum value and then diminishes with further increasing of tip speed ratio. The maximum value of power coefficient was occurring in a range of tip speed ratio 0.1- 0.2.
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
Torque coefficient was decreased with an increase in the tip speed ratio corresponding to the increasing wind speed. 30
V=2.0 m/s V=3.0 m/s V=3.5 m/s V=4.0 m/s V=4.5 m/s
25
Cp (%)
20 15 10 5 0 0
0.05
0.1
0.15 Tip speed ratio
0.2
0.25
0.3
Fig. 6 power coefficient of CR-VAWT
Cq (%)
100
V=2.0 m/s
90
V=3.0 m/s
80
V=3.5 m/s
70
V=4.0 m/s V=4.5 m/s
60 50 40 30 20 10 0 0
0.05
0.1
0.15
0.2
0.25
0.3
Tip speed ratio
Fig. 7 Torque Coefficient of CR-VAWT 5. Conclusion The cut in wind speed of CR-WT was 1.744 m/s and it is increasing when the tangential force ratio increasing. Rev up rotation period depends on wind speed and tangential force ratio. The rated rotational speed was a direct variation with wind speed and inverse variation with tangential force. The average of power coefficient of CR-WT was 14.89%. Torque coefficient was decreased with an increase in the tip speed ratio corresponding to the increasing wind speed. Acknowledgement I also gratefully acknowledge the PARA laboratory, (department of mechanical engineering, Chiang Mai University), FAME laboratory (Science and Technology Research Institute, Chiang Mai University), and Research Center of Energy and Environmental, Department of physic, Faculty of Science, Thaksin University, Phatthalung Campus.
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
References
[1] Rangsan Apakupakul. (2004). Introduction to Meteorology. Chulalongkorn University Press. ISBN 974-13-2752-8, Thailand. [2] J. F. Manwell., J. G. McGowan., and A. L. Rogers. (2002). Wind Energy Explained: John Wiley & Sons; Baffins Lane, Chic Hester, West Sussex PO19 1UD, England. [3] J.-L. Menet, 2004. A double-step Savonius rotor for local production of electricity: a design study. Renewable Energy, V 29, 843–1862. [4] Jack Park. (1975). Simplified Wind Power System for Experimenters. 2nd edition: Helion [5] V.H.Morcos and O.M.E. Abdel-Hafez, (1996). “Testing of an arrow-head vertical axis wind turbine model”. Renewable energy, Vol. 7, No 3, pp. 223-231 [6] I. P. Ficenec, (1987). “ The VAWT and its power train design”., CME, April, 34-39 [7] P. J. Musgrove, (1976). “The variable geometry vertical axis windmill”. Int. Symp. On Wind Energy System, 7-9 September [8] I. D. Mays and H. Rhodes, (1984). “Progress with the UK vertical axis wind turbine programme”. Proc. European wind Energy Conf., Hamburg, 22-26 October [9] E sm aeil A jd eh a k , (2 0 0 8 ). “A n alyzin g p ow er g en eratio n in Vertica l A xis W in d Tu rb in e (VAW T ) ” [on lin e] http://www.scribd.com/doc/8015472/VAWT [10] Smarn Sen-Ngam, (1998). “Windmill for Electrical Generation in the Rural Area” Final Research Report, Faculty of Engineering Prince of Songkla University (PSU.), Hat Yai, Songkla, THAILAND
ScienceDirect Energy Procedia 79 (2015) 149 – 156
2015 International Conference on Alternative Energy in Developing Countries and Emerging Economies
Performance Evaluation of Co-Axis Counter-Rotation Wind Turbine Tanate Chaichanaa*, Sumpun Chaitepb b
a School of Renewable Energy, Maejo University, Chiang Mai, Thailand Retired, Department of Mechanical, Faculty of Engineering, Chiang Mai University, Thailand
Abstract The present work was studied the effect of the tip speed ratio to the starting rotation, rev up rotation, power and torque coefficients of a two-shaft co-axis counter-rotating wind turbine (CR-WT). The prototype of CR-WT was tested in the open type wind tunnel with the velocities of 1.5, 2.0, 3.0, 4.0 and 5.0 m/s. CR-WT consisted of 8 blades. The blade is made of wood. It consists of 2 hubs 2 axis and 4 arms. The inner axis is clockwise rotation and outer axis is anticlockwise rotation. The inner and outer are in the identical axis. Both axes are driven the pulley by using the counter rotating gear. The analysis of the experimental results showed that the cut in wind speed of CR-WT was 1.744 m/s and it is increasing when the tangential force ratio increasing. Rev up rotation period depends on wind speed and tangential force ratio. The average of power coefficient of CR-WT was 14.89%. © 2015 Authors. Published by Elsevier This is Ltd. an open access article under the CC BY-NC-ND license © 2015The The Authors. Published byLtd. Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE. Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE
Keywords: Vertical Axis Wind Turbine, Power Coefficient, Cut-in Wind Speed, Tip Speed Ratio
1. Introduction Wind is a natural resource and it can use as an alternative energy. Wind energy is a one of the better choices to compensate fossil energy and solve a problem about the energy situation in Thailand. Other Moreover, wind energy is clean, abundant and it can reduce the global warming problem. There are 2 kinds of wind in Thailand [1], seasonal and local wind. The seasonal (monsoon) wind is consisting of north-eastern wind and south-west wind. Local wind is a wind system that's expected change in direction every such as mountain-valley breezes, land-sea breezes. Wind power is the conversion of wind energy into a useful form, such as electricity with wind turbines. Generally, wind turbines can be divided into two types based on the axis in which the turbine rotates. There are horizontal axis wind turbine (HAWT) and Vertical-axis wind turbines (VAWT), but
*
1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE doi:10.1016/j.egypro.2015.11.453
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
HAWT is more popular than the other one. VAWT have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. VAWT can work in all directions and it requires low wind speed (2 m/s) [2]. However, the VAWT has lover rotational speed and efficiency than HAWT in which a maximum tip speed is not over double of wind speed and 1 7 – % 3 0 of efficiency [3]. Nevertheless, the efficiency of VAWT will be increased by adding some equipment, such as Savonius type of main turbine, resulting in the cut in wind speed is reduced [4]. Nomenclature U
Air density (kg/m2)
A
Swept area of the wind turbine (m2)
V
Wind speed (m/s)
F
Tangential force (N)
N
Rotational speed of turbine (RPM)
r
turbine radian (m)
்ܲ
Mechanical power (Turbine Power) (W)
ܲ௪
Wind Power (W)
ܥ
Power coefficient (dimensional less)
ܥொ
Torque coefficient (dimensional less)
ܸ௨௧ି Cut in wind speed (m/s), the minimum wind speed at which the turbine first starts to rotate. XF
The divided tangential force at pulley by swept area of the wind turbine (N/m2)
ܶ௦
Time from turbine first starts rotated to a constant rotational speed (s)
ܰ
The rated rotational speed (RPM)
The development of the vertical axis wind turbine has been explored over 30 years [5-8]. Recently, the vertical axis wind turbines are more on attentiveness in term of optimization of power generation and cost effective. Ever since 1925 – 1926, the initial result was shown the various experimental work out how they design [9]. However, the Horizontal Axis Wind Turbines (HAWT) is still the favourite configuration of turbine for electrical generation. Many types of rotor have designed and tested for evaluating the behaviour and efficiency. Additional of Savonius to Darrieus type vertical wind turbine can increase the efficiency and decreased the wind speeds essentially required for starting rotation [10]. The present work studied the effect of the operating conditions to the starting rotation, rev up rotation, power and torque coefficients of a two-shaft co-axis counter-rotating wind turbine (CR-VAWT). 2. Performance Analysis The total power of the wind stream is proportional to the air density, cross section area of the swept frontal of the wind turbine perpendicular to the air flow, and the wind speed. Of which can be written as, ܲ௪ ൌ ͲǤͷߩ ܸܣଷ
(1)
The mechanical power (்ܲ ) produced by the wind turbine is a functions of tangential force and rotational speed of axis and is equal to
151
Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
்ܲ ൌ ʹߨܰܨݎȀͲ
(2)
The power coefficient (ܥ ) of a wind turbine is explained as the mechanical power output from that turbine divided by the total power accessible in the cross-section area of the wind stream input to the wind turbine. i.e.,
ܥ ൌ ்ܲ Τܲ௪ ൌ ሾʹߨܰܨݎȀͲሿȀሾͲǤͷߩ ܸܣଷ ሿ
(3)
The torque coefficient (ܥொ ) is analysis by the defined as the dividing of power coefficient of a wind turbine by the tip speed ratio (O) of the turbine. ܥொ ൌ ܥ ΤO
(4)
3. The experiment setup Two-shaft co-axis counter-rotating wind turbine (CR-VAWT) consisted of 2 rotors 4 wood blades per rotor. The model of the blade has a shape of hollowed semi-cylinder 300 mm height, 150 mm width and 1 mm of thickness. Both ends of the curved blade are attached with semi-circular plates of similar thickness. Diameter of both rotors is 150mm and swept is 0.045 m2. The inner axis is clockwise rotated and outer axis is anticlockwise rotated. Inner and outer axes are in the identical axis and have a same axis rotation. The counter rotating gear was used to connect 2 Inner and outer axis. Inner axis was connecting to pulley for measurement the power output. The component of CR-VAWT is shown in Fig. 1.
Upper Hub and Arm (76.2 mm diameter and 22 mm high 9.50 mm axis - hole diameter)
Counter rotating gear
Upper Hub Clockwise rotation
Counter clockwise rotation Lover Hub (76.2 mm diameter and 22 mm high 6.35 mm axis - hole diameter) Vertical column with 2 ball bearings
8 Curved Blades (150 mm high, 150 mm wide and 75 mm thickness).
Outer axis (6.35 mm diameter and 800 mm high) Inner axis (6.35 mm diameter and 1,000 mm high)
Pulley
Fig. 1 CR-VAWT Component
Lover Hub
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
To measure the power of the rotor, a pony brake principle is used. The difference between the dead weight and load cell readings producers the tangential force action on the pulley. Time and value were recorded and process by computer. The rotational speed was measured by a laser sensor tachometer. Wind speed in wind tunnel was control of fan with inverter and measure by a hot wire type anemometer. The testing methods were used in this research; blade pitch angle was fixing at 0o, dead weight rang 0-1 kg. Dead weight was added and corresponding rotational speed were recorded until the turbine cannot rotate by itself. The signal from load cell was amplify by electronic amplifier and recorded by an oscilloscope. The rotational speed, N, was measured by a laser type tachometer. Hot wire type anemometer was used for measuring the wind speed. The experiment setup is shown in Fig. 2.
Wind tunnel I 0.8 m. Fan
N Turbine Wind direction
0.45 m 1m
2m
Motor
Tachometer (Laser)
Anemometer (hot wire)
Load cell
Investor
T Dead weight
Wind direction Angle of attack (T)
RH meter Computer Oscilloscope
Amplifier N
Fig. 2 the experiment setup 4. Results and Discussion 4.1 Cut in speed The factor was effective to cut in wind speed of CR-VAWT is a tangential force acting the pulley or load (XF). Fig. 3 shows the variation of rotational speed of CR-VAWT with XF, the divided tangential force acting the pulley by cross section area of the swept of the wind turbine, N/m2, of the various setting wind speed of 1.5 – 4.0 m/s. Rotational speeds reach zero with a maximum value of the corresponding tangential force ratio. A rotational speed of CR-VAWT was becoming lower in curve line, but for nVAWT the rotational speeds were become lower in a straight line. The rotational speed of CR-VAWT was softly become lower when XF increase. It is a good property for keeping the mechanical system.
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156 5.0 4.5
Cut in speed (m/s)
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0
50.0
100.0
150.0
200.0
XF (N/sq-m)
Fig. 3 cut in wind speed of CR-VAWT The cut in wind speed increase when the XF increase and it became constant about 5.0 m/s. The cut in wind speed is a logarithm function of XF (N/m2) as expressed by equation 5 with the coefficient of determination (ܴଶ ) of 99.64% and with error 1.11%. Equation 5 shows that at no load the cut in wind speed were 1.74 m/s. It is the wind speed that can exert force to overcome all frictional losses of the CBVAWT. ܸ௨௧ି ൌ ሺͳǤʹͲሺ݈݊ܺܨሻሻ െ ͳǤͶ
(5)
When ܺ ܨൌ
୲ୟ୬ୣ୬୲୧ୟ୪୭୰ୡୣ୦ୣ୮୳୪୪ୣ୷ ୱ୵ୣ୮୲ୟ୰ୣୟ୭େି
ൌ
ሾିிೌ ሿ ோൈ௦
(6)
4.2 Rev up rotation The factor was effectively to rev up rotation, a phenomenon of that rotor accelerated from rest up to a constant rotational speed, which can be defined as a successful ‘start’, of Vertical Co-Axis CounterRotation Wind Turbine depends on wind speed and XF. Some researcher calls rev up rotation is a starting time sequence. At lower wind speeds the starting time sequence (ܶ௦ , s) go up more rapidly with respect to the increasing rate of XF. Conversely, at higher wind speed ܶ௦ go up with less responsive to the increasing rate of tangential force. Fig. 4 reveals the relationship between starting time sequence and XF at several of wind speeds. The relationship between starting time sequence (ܶ௦ ), XF and wind speed was explained by equation 7. The accuracy of this equation for prediction the starting time sequence is 95.62% correlation to the experimental data is shown by Fig. 4. Equation 7 cannot also be applied if both ܸ and XF are equivalent to zero. ܶ௦ ൌ ሺെͳǤͲͳሺ݈ܸ݊ሻ ͳǤͷͷሻܺ ܨ ͲǤͲͷܸ ଷǤଶ
(7)
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
V=2.0 m/s
30
V=3.0 m/s V=3.5 m/s
Starting time sequence (s)
25
V=4.0 m/s 20
V=4.5 m/s
15 10 5 0 0.0
20.0
40.0
60.0
80.0
100.0
XF (N/sq-m)
Fig. 4 Rev up rotation and ܺி of various wind speeds of CR-VAWT 4.3 Rated rotation The rated rotational speed was a direct variation with wind speed and inverse variation with tangential force. At any particular constant wind speed, the rated rotational speed decrease with the increase of tangential force ratio. On the other hand, at the constant of tangential force, the rated rotational speed was a direct variation with wind speed. Fig. 5 shows that the rotational speed of CR-VAWT with XF at deference value of wind speed. The relation of rated rotational speed, wind speed and tangential force is given by equation 8. The accuracy of equation 4 to predict the rated rotational speed is 96.59%. Equation 8 cannot also be applied if both ܸ and XF are equivalent to zero. ܰ ൌ ሺʹ͵Ǥͳʹሻܸ ሺെͲǤ͵ͳܺܨሻ ʹͷǤͲ
(8)
70.0
V=2.0 m/s V=3.0 m/s V=3.5 m/s V=4.0 m/s V=4.5 m/s
rated speed (RPM)
60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.0
50.0
100.0
150.0
200.0
XF (N/sq-m)
Figure 5 Rated rotational speed and ܺி of CR-VAWT 4.4 Power and Torque Coefficients Fig. 6 and 7 shows the power coefficient and the Torque coefficient of CR-VAWT at tip speed ratio. Power coefficient was increased to a maximum value and then diminishes with further increasing of tip speed ratio. The maximum value of power coefficient was occurring in a range of tip speed ratio 0.1- 0.2.
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Torque coefficient was decreased with an increase in the tip speed ratio corresponding to the increasing wind speed. 30
V=2.0 m/s V=3.0 m/s V=3.5 m/s V=4.0 m/s V=4.5 m/s
25
Cp (%)
20 15 10 5 0 0
0.05
0.1
0.15 Tip speed ratio
0.2
0.25
0.3
Fig. 6 power coefficient of CR-VAWT
Cq (%)
100
V=2.0 m/s
90
V=3.0 m/s
80
V=3.5 m/s
70
V=4.0 m/s V=4.5 m/s
60 50 40 30 20 10 0 0
0.05
0.1
0.15
0.2
0.25
0.3
Tip speed ratio
Fig. 7 Torque Coefficient of CR-VAWT 5. Conclusion The cut in wind speed of CR-WT was 1.744 m/s and it is increasing when the tangential force ratio increasing. Rev up rotation period depends on wind speed and tangential force ratio. The rated rotational speed was a direct variation with wind speed and inverse variation with tangential force. The average of power coefficient of CR-WT was 14.89%. Torque coefficient was decreased with an increase in the tip speed ratio corresponding to the increasing wind speed. Acknowledgement I also gratefully acknowledge the PARA laboratory, (department of mechanical engineering, Chiang Mai University), FAME laboratory (Science and Technology Research Institute, Chiang Mai University), and Research Center of Energy and Environmental, Department of physic, Faculty of Science, Thaksin University, Phatthalung Campus.
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Tanate Chaichana and Sumpun Chaitep / Energy Procedia 79 (2015) 149 – 156
References
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