[hwsv07]

I am running LES unsteady simulations and I want a time-series solution.

For a given timestep, I want to have an accurate intepretation of the evolution.

My problem is that I dunno how many iterations I should run per time step?
What do I need to judge and what parameters should I check/limit?

Appreciate all help please.

[TimCFD]

It is very important to ensure the convergence within each time step. Create some monitor points in your domain near "busy" locations (e.g. inside jets, at separation points, ...) and check the convergence of the pressure.

The pressure convergence can be checked with a plot (pressure on the y-axis and the number of iterations on the x-axis). Now you can adjust the number of inner iterations in order to get a "constant" converged pressure value within a time step.

[hwsv07]

Originally Posted by TimCFD

It is very important to ensure the convergence within each time step. Create some monitor points in your domain near "busy" locations (e.g. inside jets, at separation points, ...) and check the convergence of the pressure.

The pressure convergence can be checked with a plot (pressure on the y-axis and the number of iterations on the x-axis). Now you can adjust the number of inner iterations in order to get a "constant" converged pressure value within a time step.

Thanks. I will try that.

Im using StarCCM to run my simulations. Within it, the default residual plot monitors the residues of x,y,z momentum and continuity.

My problem involves flow separation over a bluff body. So im guessing i should place a probe at the shear layer and monitor the pressure for convergence. But is there any smart way to select the point or I just have to choose?

typically, how many inner iterations are required?
im running 20 per timestep now. Why 20? i just picked a number cos I read somewhere that for smaller global timestep, the number of inner iterations can be small.

[shahrooz.omd]

Originally Posted by hwsv07

Thanks. I will try that.

Im using StarCCM to run my simulations. Within it, the default residual plot monitors the residues of x,y,z momentum and continuity.

My problem involves flow separation over a bluff body. So im guessing i should place a probe at the shear layer and monitor the pressure for convergence. But is there any smart way to select the point or I just have to choose?

typically, how many inner iterations are required?
im running 20 per timestep now. Why 20? i just picked a number cos I read somewhere that for smaller global timestep, the number of inner iterations can be small.

yes you can choose lower iterations for each time step if you set smaller time steps, since with smaller time steps flow changes are smaller too, so the equations converge faster

[Vukosi]

I am quite new to CFD and the forum so pardon my "inappropriateness" if any exists. I am running a simulation and a set it on 1500 simulation but the solution completes before the iterations are complete, i.e at 600 iterations. What is the meaning of that? Does it mean that the solution has converged?

[shahrooz.omd]

Originally Posted by Vukosi

I am quite new to CFD and the forum so pardon my "inappropriateness" if any exists. I am running a simulation and a set it on 1500 simulation but the solution completes before the iterations are complete, i.e at 600 iterations. What is the meaning of that? Does it mean that the solution has converged?

probably residuals become smaller than a defined value.

[hwsv07]

Originally Posted by Vukosi

I am quite new to CFD and the forum so pardon my "inappropriateness" if any exists. I am running a simulation and a set it on 1500 simulation but the solution completes before the iterations are complete, i.e at 600 iterations. What is the meaning of that? Does it mean that the solution has converged?

typically u set a converging critertion and maximum number of iterations. In your case, you have set your maximum iterations to be 1500 and another criterion (e.g. pressure) to converge. So when either the max iterations is reached or your other criterion is met, your simulation stops.