Inlet Turbulence BC Calculator

Estimate initial values for turbulent kinetic energy (k), dissipation rate (ε), and specific dissipation (ω) based on empirical correlations.

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Governing Formulas

k=32(U⋅I)2k = \frac{3}{2} (U \cdot I)^2
ϵ=Cμ3/4k3/2l\epsilon = C_\mu^{3/4} \frac{k^{3/2}}{l}
ω=k1/2Cμ1/4⋅l\omega = \frac{k^{1/2}}{C_\mu^{1/4} \cdot l}
m/s
m
%

Typical ranges: 1% (low/external), 5% (medium/pipe), 10% (high/complex).

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Boundary Conditions

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Awaiting Input

Results are approximations for numerical boundary condition setup. Always verify against specific solver documentation and physical data.

Want more context on boundary conditions?

Read the CFD Simulation Setup Checklist →

Example Usage: Wind Tunnel Inlet

Scenario: You are simulating a car model in a low-speed wind tunnel. You need to set the inlet boundary conditions for a k-omega SST model.

Inputs: Velocity = 30 m/s. The wind tunnel test section is 2 m wide, so Hydraulic Diameter (Length Scale) = 2 m. The wind tunnel is high-quality, so Turbulence Intensity = 1%.

Outputs: Plug the results (k ≈ 0.135 m²/s², omega ≈ 3.0 s⁻¹) directly into your solver's inlet boundary condition fields.

Where this fits in the CFD workflow

These values are used during boundary condition setup in the solver. Once your mesh is imported, you need these estimated turbulence scalars (k, ε, ω) to accurately specify the conditions at flow inlets.

Engineering Assumptions

  • This is a screening estimate only.
  • Assumes isotropic turbulence at the inlet boundary (u' = v' = w').
  • Calculates bulk scalar values, not spatially varying boundary layer profiles.
  • Internal flow length scale is empirically approximated as l = 0.07L (suitable for fully developed pipe flow).

Documentation

Limitations

  • Very high turbulence intensities (>20%) or extremely small length scales may lead to numerical instability.
  • Does not account for transition regions or near-wall damping effects at the inlet patch.