Calculator Inputs
Use the power law for common design estimates. Use the log law when roughness length and displacement height are available.
Example Data Table
These sample cases show how speed rises with height under different terrain and profile assumptions.
| Model | Reference speed | Reference height | Target height | Profile input | Target speed | Average gradient |
|---|---|---|---|---|---|---|
| Power law | 10.00 m/s | 10 m | 80 m | α = 0.16 | 13.95 m/s | 0.056392 m/s·m-1 |
| Log law | 8.00 m/s | 10 m | 60 m | z₀ = 0.30 m, d = 0 m | 12.09 m/s | 0.081756 m/s·m-1 |
| Power law | 14.00 m/s | 15 m | 120 m | α = 0.22 | 22.12 m/s | 0.077344 m/s·m-1 |
Formula Used
Power law profile
V(z) = Vref × (z / zref)α
Use this when you know a reference speed, a reference height, and a shear exponent.
Log law profile
V(z) = Vref × ln((z - d) / z₀) / ln((zref - d) / z₀)
Use this when roughness length and displacement height better describe the terrain.
Average vertical gradient
Gradientavg = (Vtarget - Vref) / (ztarget - zref)
This shows the average rate of speed change between the two heights.
Dynamic pressure
q = 0.5 × ρ × V²
This helps connect wind speed to loading and pressure studies.
How to Use This Calculator
- Select either the power law or log law profile.
- Choose a terrain preset or keep manual inputs.
- Enter the known reference wind speed and its height.
- Enter the target height where speed must be estimated.
- Fill in α for the power law or z₀ and d for the log law.
- Set air density if you want target dynamic pressure.
- Press the calculate button to show the result above the form.
- Download the result as CSV or PDF after calculation.
FAQs
1. What does a wind speed gradient mean?
It describes how wind speed changes with height above the ground. Engineers use it to scale measured wind speeds to other elevations for design, analysis, and performance checks.
2. When should I use the power law method?
Use the power law when you need a quick engineering estimate and already have a reasonable shear exponent for the site. It is common for preliminary structural and wind resource calculations.
3. When is the log law more suitable?
The log law is better when surface roughness and displacement effects are known. It is often preferred for boundary layer studies and terrain-sensitive atmospheric calculations.
4. What is a typical value of α?
Typical values range from about 0.10 over smooth water to about 0.33 in dense urban terrain. The correct value depends on exposure, stability, and site conditions.
5. Why does wind speed usually increase with height?
Surface friction slows air near the ground. As height increases, friction effects reduce, so the flow becomes faster. Terrain roughness strongly controls how quickly that increase happens.
6. Can this calculator estimate downward speed changes?
Yes. If the target height is below the reference height, the same formulas still work. The result will show whether wind speed decreases and how steep that change becomes.
7. What units should I use?
Use meters for height, meters per second for wind speed, meters for roughness length and displacement height, and kilograms per cubic meter for air density. Keep units consistent throughout.
8. Does dynamic pressure replace a full wind load calculation?
No. Dynamic pressure is useful, but complete wind loading also depends on coefficients, exposure rules, geometry, and code requirements. Use it as one step in a wider design process.
Engineering Notes
This page estimates vertical wind profile behavior for engineering comparison. Final structural design should still follow the relevant local code, exposure category, and project-specific wind criteria.