Table 2.1: Parameters of tested water turbines (by Shionoet.al, 2002)
Solidity (σ) Chord length (C) (mm) Blade inclination angle(ɸ)(°) Height (h)
(mm)
0.20 62.8 43.7 300
0.30 94.2 43.7 300
0.40 125.7 43.7 300
0.50 157.1 43.7 300
0.40 125.7 50.0 374
0.40 125.7 60.0 544
Next, the effect of solidity σ on the water turbine characteristics was measured. Figure 2.1 shows a comparative analysis of torque characteristics for different solidity ratios at velocity 1.0 m/s, performed by Shionoet. al(2002). Figure 2.1: Torque characteristics (v=1m/s, ɸ=43.7° )
Figure2.1 reveals that the larger σis, the more the peak value of generated torque becomes, and then the peak value is shifted to lower λ. This is considered to be because as the area …show more content…
Solidity ratio comparison at low flume speeds favor’s the turbine with higher solidity. The low solidity turbine could not self-start in flow speeds up to 0.8 m/s, whereas the higher solidity turbines had no difficulty with self-starting in flow speeds of 0.5 m/s.
Hen et al. (2013) at his stage1 experiment, he tested a helical turbine which was 3 bladed, 2.2m diameter, 2.5m height with NACA0020 profile and 0.132 solidity ratio. From the experiment the maximum efficiency was found to be around 30%. In stage2 experiment, he used 3.0m diameter,3.6m height with same profile(as satge1) and 0.140 solidity ratio, he got the maximum efficiency around …show more content…
AR=H/D (2.2)
where, H is the height of the turbine. Figure2.3: Helical turbine (source: www.marineturbines.com)
For a Darrieus turbine aspect ratio has been defined as ratio of blade length to chord length. For a given cross sectional area, higher the aspect ratio, higher will be blade length. As the blade length increases blades may be subjected to deflection, vibration and stress. Again for the ease of installation and deployment one must consider size constraints.
2.2.4 Tip speed ratio (λ)
The tip speed ratio or TSR for the turbines is the ratio between the rotational speed of the tip of a blade and the actual velocity of the fluid. The tip speed ratio is related to efficiency. Higher tip speeds result in higher noise levels and require stronger blades due to large centrifugal forces. It is given by λ =ωR/U (2.3)
Whereω is the angular velocity, R is the radius of the turbine, and U is the incoming
Solidity (σ) Chord length (C) (mm) Blade inclination angle(ɸ)(°) Height (h)
(mm)
0.20 62.8 43.7 300
0.30 94.2 43.7 300
0.40 125.7 43.7 300
0.50 157.1 43.7 300
0.40 125.7 50.0 374
0.40 125.7 60.0 544
Next, the effect of solidity σ on the water turbine characteristics was measured. Figure 2.1 shows a comparative analysis of torque characteristics for different solidity ratios at velocity 1.0 m/s, performed by Shionoet. al(2002). Figure 2.1: Torque characteristics (v=1m/s, ɸ=43.7° )
Figure2.1 reveals that the larger σis, the more the peak value of generated torque becomes, and then the peak value is shifted to lower λ. This is considered to be because as the area …show more content…
Solidity ratio comparison at low flume speeds favor’s the turbine with higher solidity. The low solidity turbine could not self-start in flow speeds up to 0.8 m/s, whereas the higher solidity turbines had no difficulty with self-starting in flow speeds of 0.5 m/s.
Hen et al. (2013) at his stage1 experiment, he tested a helical turbine which was 3 bladed, 2.2m diameter, 2.5m height with NACA0020 profile and 0.132 solidity ratio. From the experiment the maximum efficiency was found to be around 30%. In stage2 experiment, he used 3.0m diameter,3.6m height with same profile(as satge1) and 0.140 solidity ratio, he got the maximum efficiency around …show more content…
AR=H/D (2.2)
where, H is the height of the turbine. Figure2.3: Helical turbine (source: www.marineturbines.com)
For a Darrieus turbine aspect ratio has been defined as ratio of blade length to chord length. For a given cross sectional area, higher the aspect ratio, higher will be blade length. As the blade length increases blades may be subjected to deflection, vibration and stress. Again for the ease of installation and deployment one must consider size constraints.
2.2.4 Tip speed ratio (λ)
The tip speed ratio or TSR for the turbines is the ratio between the rotational speed of the tip of a blade and the actual velocity of the fluid. The tip speed ratio is related to efficiency. Higher tip speeds result in higher noise levels and require stronger blades due to large centrifugal forces. It is given by λ =ωR/U (2.3)
Whereω is the angular velocity, R is the radius of the turbine, and U is the incoming