How to... increase /decrease time step size in Ansys Fluent

 Today I would like to show you how easy it is to control the  analysis in Fluent. All the necessary items can be found in the solver under Run Calculation menu. This is where the coefficients can be modified on an ongoing basis so that our residual equations are at the required level. 

Example of residual plot in Fluent 

Also thanks to this manual control, we are able to keep track of what is happening with our simulation and optimize it in terms of the time of computer calculations.

Window where U can change step size in Fluent 

Before starting the calculation, the number of steps (red frame) and the initial size of the time step (blue frame) must be determined. As starting data, I recommend a small number of steps and a very small time step size. so that you can react quickly to "events on the monitor". If our residual equations decrease with each successive step (they approach the value 0) in the next phase of calculations (after passing all steps), the size of the time step should be increased. In such cases, I personally double the value of the time step size.

If our analysis is not complicated and iterations run "sprint" on the monitor, we can increase the Reporting Interval to 10, for example, to see a little more what is happening with our analysis (gray frame).

Of course, on the other hand, if our analysis is complicated and has a convergence problem, we can increase Max Iterations / Time Step. This will allow for a greater number of solved approximations per time step - which should reduce the value of the residual equations (the orange frame).

In the next post I will present two parameters which today I have not discussed "Type" (above red frame) and Method (above blue frame). These two parameters are related to autmatization and the type of transient calculation.

As I mentioned in the previous post, Fluent offers more possibilities in terms of manual simulation control. The plasticity of breaking the analysis, defining a new step size or iteration is very high, mainly because it takes place in one window. During the simulation, we can react on an ongoing basis to what is happening with the monitors that we have defined or partial equations.