Troubleshooting
Although OpenFOAM® computational modules are stable and have been verified by thousands of users over the past 15 years, it should be remembered that simulations of 3D turbulent flow are a non-linear mathematical problem that does not always have to converge. In RWIND Simulation, we consider the numerical solution to be correct when the residual pressure drops below 0.001. This usually occurs within 500 iterations, but sometimes the calculation ends without reaching the desired residual value. There may be a number of reasons for this and there is no universal solution, but we will try to give some advice on how to proceed:
- Use the Continue Calculation function with a greater number of maximum iterations to see if the solution continues to converge or not.
- Increase the external dimensions of the computational domain, i.e. the boundaries of the wind tunnel. Automatically set dimensions may sometimes be insufficient, especially behind the model (i.e. downstream).
- Increase the density of the Finite Volume Mesh in the 'Simulation Parameters' dialog box or the Level of detail for simplified models in the 'Edit Model' dialog box.
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Try to simplify and optimise the model:
- If the model has openings (such as windows, doors, etc.) through which the flow can enter inside the model, try closing them (assuming you do not want wind flow inside the model).
- Remove small details in the model which have little or no influence on the simulation results.
- Buildings should be placed correctly on the floor of the wind tunnel or beneath this level. If the model is placed above the tunnel floor with a thin empty space between the model and the tunnel floor, the analysis may crash.
It can be assumed that the solution is acceptably converged when the following criteria are met:
Note
- The number of iterations executed is greater than the minimum number set by default (currently: 300, see the Image 'Program Options').
- The residual pressure is below the limit value set by default (currently: 0.001, see the Chapter 'General').
- The graph of the residual pressure over time no longer changes (or only very little), or it periodically oscillates around a certain mean value (see the Image below).
