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Centrifugal compressor analysis at Choke and Surge condition |
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#1 |
New Member
seunghyeon, yun
Join Date: Apr 2018
Posts: 18
Rep Power: 8 ![]() |
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. |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,816
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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
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#3 | |
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seunghyeon, yun
Join Date: Apr 2018
Posts: 18
Rep Power: 8 ![]() |
Quote:
![]() 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!! ![]() |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,816
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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.
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Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. |
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