1. What is Critical Velocity?

Definition: Critical velocity is the speed at which fluid flow transitions from laminar to turbulent regime.

Purpose: It helps engineers design fluid systems and predict flow behavior in pipes, channels, and around objects.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( V_c \) — Critical velocity (m/s)
• \( Re \) — Reynolds number (dimensionless)
• \( \eta \) — Dynamic viscosity (Pa·s)
• \( \rho \) — Fluid density (kg/m³)
• \( r \) — Characteristic radius (m)

Explanation: The formula determines the velocity at which the Reynolds number indicates transition between flow regimes.

3. Importance of Critical Velocity

Details: Understanding critical velocity is essential for designing efficient piping systems, predicting drag forces, and optimizing fluid transport.

4. Using the Calculator

Tips: Enter the Reynolds number, fluid viscosity, fluid density, and characteristic radius. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical Reynolds number for transition?
A: For pipes, transition typically occurs around Re ≈ 2300, but this can vary based on surface roughness and flow conditions.

Q2: How does viscosity affect critical velocity?
A: Higher viscosity generally increases critical velocity, making turbulent flow less likely at a given speed.

Q3: What is the characteristic radius?
A: For pipes, it's the pipe radius. For objects in flow, it's typically the object's characteristic length scale.

Q4: What are typical critical velocities in practice?
A: Water in a 1cm pipe: ~0.23 m/s; Air over a wing: depends on chord length but typically several m/s.

Q5: How does density affect critical velocity?
A: Higher density decreases critical velocity, making turbulent flow more likely at lower speeds.