The inlet angle of runner blades of a Francis turbine is

The inlet angle of runner blades of a Francis turbine is 90°. The blades are so shaped that the tangential component of velocity at blade outlet is zero. The flow velocity remains constant through out the blade passage and is equal to half of the blade velocity at runner inlet. The blade efficiency of the runner is

Given data:
B_i = 90°
V_wo = 0

V_fi = V_fo =	U_i
	2

Blade efficiency of the runner,

η_H =	V_wiu_i	=	U₁²	∴ V_wi = u_i
	gH		gH

By energy balance equation,

ρQgH = ρQV_wiU_i +	ρQV₀²
	2

gH = U_i² +	V_fo²	U_i² +	U_i²
	2		8

gH =	9	U_i²
	8

∴ η_H =	U_i²	=	8	= 0.8888
	(9/8)U_i²		9

= 88.88% ≈ 98%