Turbulence intensity is the size of velocity fluctuations relative to the mean speed:
- U is the mean speed over the measurement period.
- σu is the standard deviation of speed.
- When you paste samples, the calculator computes U and σu.
- Select your input method based on what you measured.
- Enter mean speed and either σu, urms, or samples.
- Press Calculate to show results above the form.
- Review the classification and note for site implications.
- Use CSV/PDF exports for logs, QA, or reports.
| Scenario | Mean speed (U) | Std dev (σu) | Turbulence intensity | Typical note |
|---|---|---|---|---|
| Temporary duct at bend | 3.50 m/s | 0.35 m/s | 10.00% | Check diffuser placement and sharp turns. |
| Open bay with wind gusts | 2.20 m/s | 0.55 m/s | 25.00% | Expect unsteady flow; reassess assumptions. |
| Enclosed corridor flow | 1.80 m/s | 0.06 m/s | 3.33% | Typically stable readings and consistent direction. |
Measurement context and typical uses
Construction airflow measurements often vary because of duct bends, fans, wind exposure, and obstructions. Turbulence intensity helps quantify that variability as a percentage. Use it when assessing temporary ventilation, fume extraction, dust control, and comfort airflow near occupied work areas. Higher intensity generally means the flow is less predictable and may change direction or speed quickly.
Selecting an input method for your readings
This calculator supports three practical workflows. If your instrument reports a mean speed and standard deviation, enter those values directly. If you have RMS fluctuation (u_rms), enter mean and u_rms; the tool treats u_rms as the fluctuation magnitude. If you recorded time-series samples, paste the list to compute mean, standard deviation, and additional min/max checks automatically.
Interpreting intensity values for site airflow
Intensity is computed as I = (σu / U) × 100. Values below about 5% often indicate steady flow in enclosed passages. Around 5–10% can be typical for mixed indoor conditions and moderate disturbances. Between 10–20% suggests noticeable fluctuations; consider diffuser placement, duct transitions, and equipment cycling. Above 20% indicates strongly unsteady flow and warrants cautious interpretation. Track changes after filter replacement, fan speed adjustments, or door openings to validate improvements during commissioning and checks.
Data quality checks and common pitfalls
Reliable intensity depends on a stable averaging window and consistent probe positioning. Avoid measurements too close to walls, grilles, or sharp edges unless that is your intent. Ensure mean speed is not near zero; small means can inflate the percentage. For sample lists, use enough points to represent operating conditions, and remove obvious sensor dropouts rather than real gusts.
Documentation and decision support
Use the exported CSV for logs, and the PDF for quick field reporting. Record project, area, instrument, and notes so results remain traceable. Compare zones using the same time window and units. When intensity is high, pair the metric with visual checks of smoke, anemometer direction, and ventilation layout before finalizing controls.