Troubleshooting+Flow+Solver+Convergence+Problems

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This page describes techniques used to diagnose the cause of convergence problems encountered with the Diablo flow solver.

Visualize The Problem Area in the Flow Solution
If a flow solution fails because the flow solver is producing non-physical quantities such as negative density or pressure, the following error message is usually found in the "results.solv" output file:

//**Density or Pressure Problem: trying damping factor = 0.015**//

In this case, it can be useful to visualize the area of the flow solution where the non-physical quantity appears with visualization software such as Tecplot. Below are instructions on how to do this with Tecplot:
 * 1) Download diverged flow solution and grid files to local computer with Tecplot
 * 2) Run CFD lab script "gen_surfsym_layout" to show grid and solution on geometry only
 * 3) Use Tecplot to calculate Pressure from diverged flow solution data:
 * Tecplot > Analyse > Calculate Variables > Pressure
 * 1) Turn on "Iso-Surfaces" in Tecplot
 * Tecplot > Iso-Surfaces > Details
 * Define iso-surfaces using: Pressure
 * Draw iso-surfaces at: 1 Specified Value
 * Value 1: XXX
 * Start Value 1 at a value slightly above zero and incrementally decrease until problem area is identified
 * 1) Look for problems with the grid in the vicinity of the problem area