[rnbd5782]

Hellow everyone! ^_^

Im studying the CBD(Center Body Diffuser) which simulate high altittude condition. CBD is the supersonic exhaust diffuser.

So i used Density-based type. and In oder to reduce the time required, i used steady-state solver. According to the reference paper, generally k-omega-sst model is used to analyze CBD so i used k-omega-sst model and energy equation. and for cold test, i used nitrogen for fluid materials.

The problem is "time step reduced in cell xxx". When this sentence appear, Calculation go divergence.

i can't undertand why time step reduced occur in steady-state condition.

if you have any solution about that problem, please advise me.

if you don't mind receving the Case file which i made, i would send you to your e-mail.

pleaese help me.

Thank you.

[LuckyTran]

The steady state solver actually has a temporal discretization. You'll notice an option for a Courant number in the solution controls. You might want to call it a pseudo-steady-state solver. The solution is iterated until the temporal gradients are 0. So don't be surprised that you get a funny message about the time-step while using the stead-state solver because it's not a true steady-state solver.

The difference between the steady-state solver and transient solver is that in the steady-state solver the condition that the temporal gradients are zero is imposed during the inner iterations (the steady-state condition is imposed implicitly) whereas the transient solver the gradients are free to be whatever they need to be. The steady state solver doesn't assume the temporal gradients are zero, but rather calculates the solution such that the temporal gradients become zero, thereby implicitly imposing the steady-state condition.

You should focus on why your problem is unstable/diverging but don't worry about the time-step message. It could contain some clues though.