Scientific method of turbine selection

The scientific method of turbine selection chooses the turbine type from the specific speed ($N_s$) that the site's head, discharge and unit speed demand, and then checks it against the head range, efficiency curve and cavitation limits, rather than choosing by habit.

Steps

1. Find net head and design discharge per unit from the flow duration curve (e.g. $Q_{45}$), after deducting riparian release and head losses.
2. Find unit power:

$$P = \eta_t \rho g Q H_{net}\ \text{(W)}$$

3. Choose synchronous speed for the generator: $N = \dfrac{120 f}{p}$ (e.g. 500, 600, 750, 1000 rpm at 50 Hz).
4. Compute specific speed:

$$N_s = \frac{N\sqrt{P}}{H^{5/4}}\quad (N\ \text{in rpm},\ P\ \text{in kW},\ H\ \text{in m})$$

5. Pick the turbine type whose range contains $N_s$:

6. Check with the manufacturer's head–discharge application chart, part-load efficiency, and cavitation (Thoma's $\sigma$ and setting level).
7. Adjust number of units or speed if $N_s$ falls in an overlap zone, and compare cost.