What is the blade length (bo) limits on crossflow turbine ?

By Ahmad Suhendra

Crossflow turbine blade has a length limit that must be met in the design, for the turbine at an angle α1=16 o, nozzles coef. kc = 0.98 and k = 0.075 to 0.10 are as follows:

1). C (m/sec) = kc.(2.g.H)^0.5
2). Phi.D1.Nt / 60 = (C. cos α1)/2

Then:
The diameter of blade is :
3). D1 (m) = 39.85 H ^ 0.5 / Nt

Blade length (bo) is obtained from the following equation(4)
4). Q(m^3/sec ) =(So.bo)[ kc ( 2.g.H )^0.5 ]
5). So(m) = k D1

By entering the equation (5) and (3) into equation (4) is obtained :
The blade length (bo) limits is :

6). bo = ( 0.058 Q.Nt / H ) to ( 0.077 Q.Nt / H )

Where:

• g is the constant of gravity 9.8 m/s^2
• C is the absolute velocity of water (m/sec)
• Phi is 3.14
• Nt is the nominal turbine speed (rpm)
• D1 is the diameter of Disc (m)
• So is the thickness of the water jet (m)
• H is the net head (m)

Ref : Edy Sunarto , dkk,” Pedoman Rekayasa Tenaga Air (Hydropower Engineering Guidelines) ”, UPT Hidro Elektris BPPT, Jakarta 1991