Study Wind Tunnel Calculator

Overview

This tool implements a simplified, physically consistent method for preliminary sizing of open-circuit, low-speed wind tunnels. All tunnel sections are defined relative to the test section, which acts as the reference for flow conditions, loss coefficients, and power scaling.

For a specified test-section Mach number and geometry, the method propagates flow conditions upstream and downstream through the contraction and diffuser. Section-by-section losses are computed using empirical correlations from the wind tunnel design literature and combined into a single total loss coefficient.

The total loss coefficient defines an energy ratio which links test-section dynamic pressure to overall tunnel pressure losses. This enables a consistent estimate of required fan/motor power for a given test-section condition.

Method

The tunnel is modelled as three primary sections:

• Contraction
• Test section
• Diffuser

For each section, the local Mach number, Reynolds number, and Darcy friction factor are evaluated from the local cross-sectional area and length. Loss coefficients for the contraction, test section, and diffuser are then computed using established empirical correlations. All losses are referenced to the test-section dynamic pressure and summed into a single total loss coefficient for the tunnel.

The energy ratio is defined as the inverse of the total loss coefficient and is used to estimate total pressure drop and motor power required to achieve the specified test-section conditions.

Model assumptions

• Low-speed, open-circuit configuration (subsonic; intended for modest Mach numbers).
• Losses are referenced to test-section dynamic pressure for consistent summation.
• Friction factors and loss correlations are empirical and represent engineering approximations.
• Steady flow assumption; does not model unsteady effects, fan curves, or acoustics.

Intended use

This tool is intended for rough preliminary sizing only. It is suitable for early-stage feasibility studies, comparison of candidate tunnel geometries, and estimation of overall tunnel length/footprint and order-of-magnitude fan power requirements.

It is aimed at students, hobbyists, and academic users who want a transparent sizing calculation based on common wind tunnel design relations.

Limitations

• Does not include screens/honeycombs, corners, inlet/exit losses, or facility-specific ducting effects.
• Does not include fan performance curves, motor selection, noise, or structural constraints.
• Boundary-layer blockage is treated using simplified correlations and should be checked for validity.
• Not a substitute for detailed CFD, structural design, or experimental validation.

References

The method is based on standard low-speed wind tunnel design texts and supporting technical reports, including empirical loss correlations for contractions and diffusers. A full reference list will be provided once the tool and accompanying documentation are finalised.