Page 327 - Fluid Mechanics and Thermodynamics of Turbomachinery

308 Fluid Mechanics, Thermodynamics of Turbomachinery
(2) the power output, corrected using Moody’s equation to allow for scale effects (assume
a value for n D 0.2);
(3) the suction specific speed  ss .

(d) The prototype turbine operates in water at 30 ° C when the barometric pressure is 95 kPa.
Determine the necessary depth of submergence of that part of the turbine mostly likely to be
prone to cavitation.
8. The preliminary design of a turbine for a new hydro-electric power scheme has under
consideration a vertical-shaft Francis turbine with a hydraulic power output of 200 MW
under an effective head of 110 m. For this particular design a specific speed,  s D 0.9 (rad),
is selected for optimum efficiency. At runner inlet the ratio of the absolute velocity to
the spouting velocity is 0.77, the absolute flow angle is 68 deg and the ratio of the blade
speed to the spouting velocity is 0.6583. At runner outlet the absolute flow is to be without
swirl.
Determine:
(1) the hydraulic efficiency of the rotor;
(2) the rotational speed and diameter of the rotor;
(3) the volume flow rate of water;
(4) the axial length of the vanes at inlet.
9. A Kaplan turbine designed with a shape factor (power specific speed) of 3.0 (rad), a
runner tip diameter of 4.4 m and a hub diameter of 2.0 m, operates with a net head of 20 m
and a shaft speed of 150 rev/min. The absolute flow at runner exit is axial. Assuming that
the hydraulic efficiency is 90% and the mechanical efficiency is 99%, determine:
(1) the volume flow rate and shaft power output;
(2) the relative flow angles at the runner inlet and outlet at the hub, the mean radius and at
the tip.