[YOUNS]

Hello.

I'm working on centrifugal compressor of the turbocharger for car.
Geometry has 4 domains :
1. Inblock(Inlet domain) 2. Passage(Blade) 3. Outblock(Diffuser) 4. Volute

Condition for analysis is Inlet total pressure and Outlet mass flow rate.
0. steady state
1. Inlet total pressure: 1atm(reference pressure: 0atm)
2. Outlet mass flow rate: 26.7 g/s(@Surge), 69.9 g/s(@Choke)
3. Rotating Speed: 230,000 rpm
4. Frozen Rotor condition at all interfaces.
5. Passage domain and Outblock(Wall Configuration: Yes) domain are
rotating condition.

Design point of this compressor is 46.0 g/s and 230,000 rpm.
In this case, I have a very good converged result and analysis result at surge condition is so so.
But, Problem is choke condition.
I tried to input for initial condition of converged result at design point.
But.... In this case isn't convergence...
So, I tried to condition that has 57.95 g/s condition then It is convergence.
Now, I tried to 63.925 g/s...

How to set analysis condition if i should get converged result?

Thanks for read.

[ghorrocks]

Choked flow is often tricky to converge. The standard tips for improving numerical stability apply:
* Improve mesh quality
* Smaller time steps
* Double precision numerics
* Better initial condition

[YOUNS]

Originally Posted by ghorrocks

Choked flow is often tricky to converge. The standard tips for improving numerical stability apply:
* Improve mesh quality
* Smaller time steps
* Double precision numerics
* Better initial condition

Thanks your reply

I have a one more question.
To my knowledge, it recommend that setting the time step is 1/RPM(rad/s) from cfx guide.
But, I used to very large time step(about 20) than recommend value.
This time step give good convergence.

How about your opinion this situation?
I am confuse always

Thanks for read
Have a nice day!!

[ghorrocks]

If it is a steady state simulation and it converges with a large time step then that is OK. It means your simulation is quite stable and should converge quickly.