How the Strouhal Number Calculator Works

This Strouhal Number Calculator helps you compute the Strouhal number (St), a key dimensionless value in fluid dynamics and aerodynamics. It describes oscillating flow phenomena, especially vortex shedding, and is critical for analyzing flow-induced vibrations, resonance, and wake patterns in engineering systems.

Steps to Use the Strouhal Number Calculator

Enter the vortex shedding frequency (f in Hz), which is the rate at which vortices are released from a body immersed in a fluid.
Input the characteristic length (L in meters), often the diameter for cylindrical objects or width for flat plates.
Input the free-stream velocity of the fluid (V in m/s), which is the speed of the fluid far from the influence of the object.
Click the "Calculate Strouhal Number" button to determine the result.
The Strouhal Number Calculator will return a dimensionless value that characterizes the unsteady nature of the flow.

Strouhal number calculator illustration showing vortex shedding behind a cylinder — Visualization of vortex shedding and flow oscillation. Source: Wikipedia

Strouhal Number Formula

The Strouhal number (St) is calculated using the following formula:

St = (f × L) / V

Where:

St = Strouhal number (dimensionless)
f = vortex shedding frequency in Hertz (Hz)
L = characteristic length in meters (m)
V = flow velocity in meters per second (m/s)

Understanding the Importance of the Strouhal Number

The Strouhal number provides insight into the nature of flow around objects, especially bluff bodies. It is particularly useful for:

Predicting vortex-induced vibrations in structures such as chimneys, bridges, and towers.
Designing efficient heat exchangers and fluid flow meters.
Studying flow behavior in animal locomotion, such as fish swimming or bird flight.
Optimizing aerodynamic shapes in automotive and aerospace engineering.

Typical Strouhal Number Values

The Strouhal number typically falls within a narrow range for certain shapes:

For a circular cylinder: St ≈ 0.2 across a wide Reynolds number range.
For flat plates and rectangular objects: St varies between 0.1 and 0.3.

Example: How to Use the Strouhal Number Calculator

Imagine a cylindrical rod exposed to air flow with a shedding frequency of 50 Hz, a diameter of 0.05 m, and a free-stream velocity of 10 m/s.

St = (50 × 0.05) / 10 = 0.25

This result indicates the presence of a typical bluff body vortex shedding behavior.

Why Use an Online Strouhal Number Calculator?

Manually calculating the Strouhal number can be time-consuming, especially when analyzing multiple cases or performing simulations. Our fast, easy-to-use Strouhal Number Calculator provides:

Instant calculations for engineers, students, and researchers.
A user-friendly interface that reduces the risk of manual errors.
Useful insights into fluid flow patterns and resonance risk in structural designs.

Note: This Strouhal Number Calculator assumes flow over a stationary object in a steady, uniform stream. It is most applicable in incompressible fluid scenarios such as water and low-speed air flows.

If you're working in computational fluid dynamics (CFD), wind tunnel testing, or structural vibration analysis, this Strouhal number calculator is a must-have tool in your engineering toolbox.