Step time and first order upwind

salvaCCM · January 9, 2021, 11:35

I am currently studying the flow inside a diffuser of a plane’s motor . As I know the phisical conditions of the air at 3500ft my boundary conditions for the inlet and oulet are pressure inlet and mass flow outlet.
However, an iteration problem occurs when trying to obtain residuals and convergence ( Floating problem (divided by zero)). I have read that this can be solved by changing the step time or using a first order upwind scheme but i dont know where to change those parameters in Star CCM+
Any idea? Any other possible solution for the problem?
Thnx

koful · January 10, 2021, 05:57

Hi.

If you choose impicit unsteady from physics, you can find time step size under "solver->implicit unsteady".

also you can increase time step iterations from "stopping criteria->maximum inner iteration"

Lastly you can choose adaptive time step from physics. The settings will be appear under "solvers".

January 9, 2021, 11:35	Step time and first order upwind	#1
salvaCCM New Member Salvador Gonzalez Ciscar Join Date: Jan 2021 Posts: 1 Rep Power: 0	I am currently studying the flow inside a diffuser of a plane’s motor . As I know the phisical conditions of the air at 3500ft my boundary conditions for the inlet and oulet are pressure inlet and mass flow outlet. However, an iteration problem occurs when trying to obtain residuals and convergence ( Floating problem (divided by zero)). I have read that this can be solved by changing the step time or using a first order upwind scheme but i dont know where to change those parameters in Star CCM+ Any idea? Any other possible solution for the problem? Thnx

January 10, 2021, 05:57		#2
koful Member Join Date: Jun 2014 Location: Turkey Posts: 43 Rep Power: 11	Hi. If you choose impicit unsteady from physics, you can find time step size under "solver->implicit unsteady". also you can increase time step iterations from "stopping criteria->maximum inner iteration" Lastly you can choose adaptive time step from physics. The settings will be appear under "solvers". salvaCCM likes this.