| Scenario | Inputs | Computed flow | Notes |
|---|---|---|---|
| Power & Head | Power 500 kW, Head 25 m, ηt 90%, ηg 98% | ≈ 2.3993 m³/s (≈ 2,399 L/s) | Water 1000 kg/m³, g 9.80665 m/s² |
| Area & Velocity | Diameter 1.0 m, Velocity 2.5 m/s | ≈ 1.9635 m³/s (≈ 69.34 cfs) | Uses A = πD²/4 |
- Select a calculation method that matches your available data.
- Enter project name, then fill the required fields for that method.
- Adjust density and gravity if your fluid or location differs.
- For the power method, optionally enter a target velocity to get a diameter suggestion.
- Press Calculate to display results above the form.
- Use the download buttons in the result panel for CSV or PDF exports.
Selecting the measurement method
Turbine discharge can be estimated from energy conversion or from section hydraulics. Use Power & Head when you know delivered power, net head, and realistic efficiencies. Use Area & Velocity when you can measure a representative cross‑section and average velocity at the intake or penstock.
Power, head, and efficiency impacts
For hydropower, the governing relationship is Q = P /(ρ·g·H·η). With water at 1000 kg/m³ and g = 9.80665 m/s², a 500 kW unit at 25 m net head with 90% turbine and 98% generator efficiency gives roughly 2.40 m³/s. If overall efficiency drops to 0.80, flow rises about 12.5% for the same power. A 1 m head error at 25 m changes Q by about 4%, so confirm pressure and elevation references.
Area, velocity, and intake sizing
The hydraulic method uses Q = A·V. For a circular conduit, A = πD²/4. A 1.0 m diameter section has 0.785 m² area; at 2.5 m/s the computed flow is about 1.96 m³/s. When you have a target velocity, the recommended diameter is D = √(4Q/(πV)), useful for preliminary intake sizing. If you measure velocity with a meter, sample multiple points to reduce bias from nonuniform profiles.
Unit consistency and reporting outputs
Construction documents often mix kW, hp, meters, and feet. This calculator converts all inputs to SI internally, then reports flow as m³/s, L/s, m³/h, and cfs for field coordination. Exported CSV supports quick quantity checks, while the PDF snapshot suits submittals and progress records. Record instrument calibration dates for traceable field results.
Construction planning checks
Verify that net head reflects losses from bends, valves, trash racks, and friction. Compare computed penstock velocity against project limits to manage surge, vibration, and erosion. Keep notes on assumed efficiencies and operating point, and rerun scenarios during commissioning to confirm the installed turbine matches design performance. Also check tailwater levels and cavitation margins when flows increase.
Use Power & Head when you have reliable power output and net head estimates. Use Area & Velocity when you can measure a section and average velocity directly. For commissioning, compare both methods to catch sensor or unit-entry errors.
Separating them keeps assumptions transparent. Turbine efficiency reflects hydraulic-to-shaft conversion, while generator efficiency reflects shaft-to-electric conversion. Multiplying both gives overall efficiency used in the power method.
For clean water, 1000 kg/m³ is a common default. Adjust for temperature, sediment, or other fluids if known. Small density changes usually shift flow modestly compared with head and efficiency errors.
When you provide a target velocity, the tool rearranges Q = A·V to solve for diameter. It returns a circular-equivalent diameter that would carry the computed flow at your chosen velocity.
Yes. Inputs can be entered in feet, inches, or horsepower where offered. The calculator converts everything to SI internally, then reports flow in multiple units for coordination.
Confirm net head is realistic and includes losses. Recheck efficiency values and power units (kW vs MW). For area-velocity, verify the section size and that the velocity represents an average, not a peak reading.