Calculator Inputs
Enter obstruction, airflow, and recovery assumptions. Results appear above this form after calculation.
Example Data Table
These examples use the same model as the calculator so you can compare common site conditions.
| Case | Velocity (m/s) | Width × Height (m) | Distance (m) | Porosity (%) | Wake velocity (m/s) | Velocity loss (%) | Pressure loss (Pa) |
|---|---|---|---|---|---|---|---|
| Scaffold screen | 9.50 | 14.00 × 8.00 | 20.00 | 30.00 | 7.14 | 24.84 | 24.05 |
| Solid site wall | 11.00 | 22.00 × 6.00 | 18.00 | 0.00 | 6.79 | 38.24 | 45.84 |
| Building edge | 13.50 | 28.00 × 16.00 | 40.00 | 5.00 | 8.71 | 35.47 | 65.14 |
Formula Used
This calculator uses a practical wake-loss screening model for construction airflow studies. It estimates how an obstruction reduces downstream velocity and dynamic pressure, then shows recovery with distance. It is best for early comparisons, not final certification.
Core geometry
Projected area: A = W × H
Equivalent diameter: De = √(4A / π)
Wake diameter: Dw = De + 2kx
Wake expansion and deficit
Expansion factor: k = 0.04 + 0.45TI + 0.03φ
Spread term: (De / (De + 2kx))²
Deficit factor: C × spread term × distance correction
Velocity and pressure
Wake velocity: Vw = V0(1 − deficit)
Dynamic pressure: q = 0.5ρV²
Pressure loss: Δq = q0 − qw
Recovery and energy indicator
Recovery percentage: 100 × Vw / V0
Energy-based loss: 100 × (1 − (Vw / V0)³)
Wake flow rate: Q = Aw × Vw
Symbols: W = width, H = height, x = downstream distance, TI = turbulence intensity as a decimal, φ = porosity as a decimal, ρ = air density, and C = combined strength term based on drag, exposure, shape, and porosity.
How to Use This Calculator
- Enter the approach airflow speed before the obstruction.
- Input obstruction width and height using projected dimensions.
- Set the downstream distance for the assessment point.
- Choose a drag coefficient that matches the barrier or façade.
- Enter porosity for screens, wraps, mesh, or open panels.
- Adjust turbulence, exposure, and shape factors for site conditions.
- Set the graph range to visualize recovery over distance.
- Click calculate to show results above the form.
- Use the CSV and PDF buttons to save the current output.
- Compare alternatives by changing porosity, distance, or geometry.
Frequently Asked Questions
1) What does this wake loss calculator estimate?
It estimates downstream airflow reduction caused by an obstruction such as a screen, wall, scaffold wrap, or building edge. It reports wake velocity, percent loss, pressure drop, wake spread, recovery, and an energy-based loss indicator using a practical screening model.
2) Is this a replacement for CFD or wind-tunnel testing?
No. It is a quick planning tool, not a full fluid simulation. Use it for early comparisons, option screening, and rough safety discussions. Critical projects should still be checked against governing requirements, specialist advice, detailed simulation, or physical testing.
3) Why do porosity and turbulence change the answer?
Porosity lets some air pass through the obstruction, which usually softens the deepest wake. Turbulence mixes air faster, so the wake often spreads wider while also recovering sooner downstream.
4) What drag coefficient should I enter?
Use a value that matches the obstruction type and assumption source. Solid rectangular faces often use higher values than open screens. Manufacturer data, engineering references, or consistent project assumptions are better than guesswork.
5) Why can energy-based loss be much higher than velocity loss?
Moving air power changes approximately with the cube of velocity. That means a moderate drop in velocity can create a noticeably larger energy-related loss percentage. This is useful when discussing performance or sheltering intensity.
6) Can I use this for temporary works and site barriers?
Yes. It is useful for scaffold sheeting, acoustic barriers, hoardings, temporary enclosures, wind screens, and similar site elements when you want quick comparisons between spacing, porosity, and setback options.
7) Which units does the calculator use?
Inputs use metric units: meters, meters per second, kilograms per cubic meter, and percentages. Results include Pascals for pressure loss, square meters for wake area, cubic meters per second for flow, and watts for the power-deficit indicator.
8) How should I read the Plotly graph?
The graph shows how wake velocity and energy-based loss change as the assessment point moves farther downstream. Faster recovery means the blockage effect weakens sooner. Use the curve to compare design choices and setback distances.