Hydro Turbine Design Chart: Specific-Speed Nomogram

Site Parameters

Gross head H 80 m

Flow rate Q 12.0 m³/s

Runner speed N 500 rpm

Turbine choice

Recommended Runner

Francis

Medium head, radial-axial reaction runner

Live Readouts

Specific speed Ns

Runner efficiency η

Power output P

0 MW

Torque τ

0 kN·m

How to read the chart

This is the same turbine-selection physics as the 3D spinning-runner view, drawn instead as the log-log design chart a hydro engineer actually uses to pick hardware. The left panel plots gross head H against flow rate Q on log axes; drag the white dot anywhere on it to set both sliders at once. The background is shaded by which runner family the live specific speed calls for at your current rotational speed N:

P = ρ · g · H · Q                  (hydraulic power, ρ=1000, g=9.81)
Ns = N · √P / H^(5/4)               (metric specific speed)
Since Ns ∝ H^(-3/4) at fixed Q, N — each Ns boundary
is a straight power-law curve on this log-log chart.

Ns < ~30 (top region, high head) — Pelton impulse wheel.
~30–450 (middle band) — Francis reaction runner.
Ns > ~450 (bottom region, low head) — Kaplan axial propeller.

The top-right panel plots each runner family's own efficiency curve against Ns — Pelton stays flat and wide, Francis and Kaplan peak sharply near their design point and fall off fast outside it. A marker on the active curve shows exactly how far off-design your current point sits. The bottom-right panel is a schematic 2D cross-section of the recommended (or forced) runner, spinning at a rate proportional to N: Pelton buckets struck by a needle jet, a Francis vane ring, or Kaplan blades whose pitch visibly flattens as flow rises — the identical geometric behaviour as the 3D model, redrawn as a flat diagram rather than a camera view of it.

Pelton region (Ns<30) Francis region (30–450) Kaplan region (Ns>450)

Drag the dot to set H & Q