Change Boundary Conditions

Changing the boundary pressures or flow rates can help give insight into what is giving the model trouble.

If increasing the flowrate in a system resolves a convergence issue, it may indicate the convergence issues in the original system are due to narrow tolerances around low flowrates. In this case, using an Absolute Tolerance may be beneficial. If decreasing the flowrate resolves a convergence issue, it may indicate the original flowrate is above the sonic flowrate. In this case, it may help to determine what the sonic flowrate is, and compare the desired flowrate against that value to determine if the desired value is physically realistic.

If increasing or decreasing all boundary pressures by a uniform amount resolves a convergence issue, it may indicate the convergence issues in the original system are due to difficulties finding valid fluid properties at extreme conditions. In this case, it may help to try using a different fluid property library or Equation of State.