C HAPTER –7
7.3 Analysis of performance characteristics
The torque and power characteristics of the newly developed SSWT are shown in Figures 7.4 and 7.5. It is observed that at 6.2 m/s, the CPmax is found to be 0.30 at TSR = 0.81. As discussed in chapter-6, at this wind speed, for modified Bach and conventional SSWTs, the CPmax are 0.29 (TSR = 0.78), and 0.23 (TSR = 0.71), respectively.
Figure 7.4: Variation of CT for the newly developed SSWT at V = 6.2 m/s
Figure 7.5: Variation of CP for the newly developed SSWT at V = 6.2 m/s
D 1.1 D
0.2 d d
D 1.1 D
0.2 d d
0.3 D
1.1 DD
0.172 D 0.075 D 0.32 D
D 1.1 D
0.1 d 0.4 d
135° 0.42 d
d
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR
Newly developed SSWT
V= 6.2 m/s
Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Newly developed SSWT
V= 6.2 m/s Blockage corrected data
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Figures 7.6 and 7.7 show the torque and power coefficients of newly developed SSWT at V = 3.8 m/s. These performance indices are also presented for other tested turbines. It may be observed that the torque coefficient values decrease with the increase of TSR. This is mainly caused by the gradual loads applied to the turbine shaft, which in turn, reduces the rotational speed of the turbine. On the other hand, the power coefficient increases with an increase of TSR up to a certain maximum value, beyond which it decreases with further increase in TSR.
The newly developed blade gives a CPmax of 0.27 at TSR = 0.77. At this low wind speed (V = 3.8 m/s), the modified Bach type has shown a nearly similar performance to the newly developed SSWT; whereas, the conventional semicircular blade has displayed the lowest power and torque coefficients. The performance gains of the newly developed SSWT over conventional, semi-elliptic and Benesh type turbines are found to be 28.6%, 17.4% and 3.8%, respectively.
Figure 7.6: Variation of CT at V = 3.8 m/s Figure 7.7: Variation of CP at V = 3.8 m/s
Similarly, Figures 7.8 to 7.21 demonstrate the variations of torque and power coefficients at V = 4.5 m/s, 5.3 m/s, 6.2 m/s, 7.0 m/s, 7.8 m/s, 8.9 m/s, and 9.8 m/s, respectively. In all the cases, the newly developed two-bladed turbine shows an improvement in the power and torque coefficients as compared to other tested turbines.
With blockage correction, a CPmax of 0.31 is obtained for the newly developed turbine at V = 7.8 m/s and TSR = 0.82. In contrary, the CPmax for modified Bach type, Benesh type, semi- elliptic and conventional blade profiles are found to be 0.30, 0.29, 0.26 and 0.23, respectively at V = 7.8 m/s.
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 3.8 m/s Blockage corrected data
0.06 0.11 0.16 0.21 0.26 0.31
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 3.8 m/s
Blockage corrected data
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Figure 7.8: Variation of CT at V = 4.5 m/s Figure 7.9: Variation of CP at V = 4.5 m/s
Figure 7.10: Variation of CT at V = 5.3 m/s Figure 7.11: Variation of CP at V = 5.3 m/s
Figure 7.12: Variation of CT at V = 6.2 m/s Figure 7.13: Variation of CP at V = 6.2 m/s 0.00
0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 4.5 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 4.5 m/s
Blockage corrected data
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 5.3 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 5.3 m/s
Blockage corrected data
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 6.2 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 6.2 m/s
Blockage corrected data
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Figure 7.14: Variation of CT at V = 7.0 m/s Figure 7.15: Variation of CP at V = 7.0 m/s
Figure 7.16: Variation of CT at V = 7.8 m/s Figure 7.17: Variation of CP at V = 7.8 m/s
Figure 7.18: Variation of CT at V = 8.9 m/s Figure 7.19: Variation of CP at V = 8.9 m/s 0.00
0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 7.0 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 7.0 m/s
Blockage corrected data
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 7.8 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 7.8 m/s
Blockage corrected data
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 8.9 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 8.9 m/s
Blockage corrected data
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Figure 7.20: Variation of CT at V = 9.8 m/s Figure 7.21: Variation of CP at V = 9.8 m/s
Table 7.1 shows the values of maximum power coefficients corresponding to various TSRs at V = 3.8 m/s to 9.8 m/s. It is observed that for the new developed blade profile, the maximum power coefficients are obtained in the range of TSR = 0.74–0.83. Whereas, for modified Bach, Benesh, semi-elliptic and conventional type turbines, the CPmax values are found at TSR= 0.66–0.73, 0.69–0.75, 0.71–0.81 and 0.72–0.81, respectively. Thus, in each case, there is a shift in the range of optimum TSR. Figure 7.22 indicates the effect of wind speed on dynamic performances of the newly developed blade profile. It is seen that with the increase of wind speed up to V = 7.8 m/s, the CPmax increases, beyond which it again decreases.
Table 7.1: Maximum power coefficients corresponding to tip speed ratios (blockage corrected data) Blade profile V = 3.8 m/s V = 5.3 m/s V = 6.2 m/s V = 7.8 m/s V = 9.8 m/s
CPmax TSR CPmax TSR CPmax TSR CPmax TSR CPmax TSR New SSWT 0.27 0.77 0.28 0.75 0.30 0.81 0.31 0.82 0.29 0.79 Modified Bach 0.27 0.75 0.27 0.72 0.29 0.78 0.30 0.80 0.28 0.77 Benesh 0.26 0.73 0.26 0.72 0.28 0.77 0.29 0.80 0.27 0.77 Semi-elliptic 0.23 0.73 0.23 0.70 0.25 0.73 0.26 0.75 0.24 0.72 Conventional 0.21 0.66 0.22 0.67 0.23 0.71 0.23 0.73 0.22 0.69
However, without any blockage correction, the calculated experimental data representing the maximum values of torque and power coefficients are shown in Figures 7.23 and 7.24. For the newly developed, modified Bach, Benesh, semi-elliptic, and conventional bladed turbines, the CPmax values are found to be 0.34, 0.33, 0.32, 0.28 and 0.26, respectively.
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0 0.2 0.4 0.6 0.8 1 1.2
CT
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed
V= 9.8 m/s Blockage corrected data
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 0.2 0.4 0.6 0.8 1 1.2
CP
TSR Conventional Semi-elliptic Benesh type Modified Bach type Newly developed V= 9.8 m/s
Blockage corrected data
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Figure 7.22: Effect of wind speed on the performance of SSWTs
Figure 7.23: Variation of CT without blockage correction at V = 7.8 m/s
Figure 7.24: Variation of CP without blockage correction at V = 7.8 m/s