CFL Condition

Check whether the current time step is stable for explicit integration.

visual calculatorNumerics & Stability

Read the flow shape before trusting the number.

This page turns a CFD setup into regime, scale, and dominant-effect cues. Adjust the calculator below and compare the moving graphic with the computed result.

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model

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CFLnumericsstability

formula

KaTeX rendered

\begin{aligned}\text{C = u dt / dx}\end{aligned}

ASCII source

C = u dt / dx

u — wave speed (m/s)Δt — time step (s)Δx — grid spacing (m)C_max (e.g., 1.0 advect, 0.5 RK4)

C (current)

0.1000 ✓ stable

Δt_max for current Δx

5.000e-3 s

Explicit Euler 1-D advection: C_max = 1. Higher-order RK (e.g., RK4) typically allows C ≈ 1.4–2 for advection, but viscous & non-linear terms add tighter limits.

CFL numerics stability