An ideal wind-turbine, 12 m in diameter, operates at a theoretical efficiency ($$\eta_{th}$$) (equation given below) of 50% in $$u_2$$ = 14 m/s wind. If the air density is 1.2 kg/$$m^3$$ and
$$\eta_{th} = \frac{(u_1 + u_4)(u_1^2 - u_4^2)}{2u_1^3}$$
$$u_2 = u_3 = (u_1 + u_4) / 2$$
$$P_1 = P_4 = P_{atm}$$
Determine,
a) The axial force on the windmill. (assume uniform flow at positions)
b) The mean (gage) pressures immediately in front of ($$P_2 - P_{atm}$$) and behind ($$P_3 - P_{atm}$$) the disc,
c) The shaft power developed by the turbine.