Time-Step Budget Visualizer

Compare advective CFL, acoustic CFL, and diffusion Fourier limits to identify the active time-step bottleneck.

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.

input scale

model

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time stepCFLFourierexplicit solver

formula

KaTeX rendered

\begin{aligned}\text{dt\_max = min(C dx/U}\\[0.35em]\text{C\_a dx/(a+U)}\\[0.35em]\text{Fo dx\^{}2/nu)}\end{aligned}

ASCII source

dt_max = min(C dx/U, C_a dx/(a+U), Fo dx^2/nu)

dt current (s)dx min (m)|U|max (m/s)sound speed a (m/s)nu or alpha (m^2/s)CFL maxacoustic CFL maxFo max

limiting dt (s)

7.792e-6

current / limit

1283.3%

limiting physics

acoustic CFL

advective dt (s)

8.889e-5

acoustic dt (s)

7.792e-6

diffusion dt (s)

0.4167

current CFL

0.9000

current Fo

6.000e-5

For compressible explicit solvers, acoustic speed often dominates. For viscous DNS/LES near walls, the diffusion limit can become the smallest budget.

time step CFL Fourier explicit solver