Free Engineering Simulation Tutorial - Opensource Software & Simulation Guides

"How long will this CFD run take?" — the question every engineer asks before hitting Solve, and the one nobody can answer confidently. Guess too low and you blow your deadline (or your cloud-compute budget); guess too high and you over-provision expensive HPC nodes. This free CFD Time-Step & Runtime Estimator turns that guess into an engineering estimate: enter your CFL target, mesh size, physical time and core count, and it computes the stable time step , the number of steps , and a wall-clock time — plus a calibration mode that uses a short test run to make the estimate genuinely accurate. Figure 1 CFD Time Step and Run time Calculator Table of Contents The Runtime Estimator Why Estimate Runtime? Step 1: The CFL Time Step Step 2: Number of Time Steps Step 3: Cost Per Step Step 4: Parallel Scaling The Calibration Trick Worked Example Common Mistakes FAQ The Runtime Estimator Use Estimate mode f...

Your CFD simulation was running fine — then the residuals exploded to infinity and everything turned to NaN. Nine times out of ten, the culprit is a time step that's too large, violating the CFL condition . The Courant–Friedrichs–Lewy number is the single most important control on the stability of any transient (time-marching) simulation, and getting it right is the difference between a clean run and a wasted afternoon. This guide gives you a free CFL calculator (validated against the standard formulas), explains the condition in plain language, and shows you exactly how to choose a stable, efficient time step. Figure 1. The Courant number measures how far the flow travels per time step relative to the cell size. Keep it below 1 (explicit solvers) and the simulation stays stable; exceed it and the solution diverges. Table of Contents The CFL / Courant Number Calculator What Is the CFL / Courant Number? The CFL Stability Condition The Formula...