Steam Turbine Simulation

AliMobasher · November 21, 2020, 01:57

Dear all, I'm using Ansys CFX to simulate one stage of a steam turbine in a real operating condition. I'm using H2Olg as a homogeneous fluid and equilibrium simulation is considered. In inlet boundary when I use H2Og as "equilibrium constraint" and H2Ol as "equilibrium Fraction" everything is ok, but when I switch these options, the solver divergs with the error of "Maximum Mach Number". What's Wrong?
Is it important to choose H2Og or H2Ol as "equilibrium Fraction"???
If "yes" which of H2Ol or H2Og should be selected as "equilibrium fraction"???

Gert-Jan · November 22, 2020, 12:02

It depends.
In general, I would solve the fraction with most of the volume, and constraint with least volume, which is mostly the liquid. But if, by, far most of the mass is present in the liquid, then I could turn it around.

It would be interesting to know how the mass on the inlet is distributed.

AliMobasher · November 29, 2020, 12:23

Thanks Gert-Jan for your reply.
Yes it's rational to choose the dominant volume as constraint but in my case I have convergence problem with this choice. It's interesting to mention that I have a case solved with two options and the results are exactly same. but in another case I receive "Mach number error" with vapor phase as "fraction". It's more interesting to know that in this case the flow is certainly superheat and no liquid phase presents.

November 21, 2020, 01:57	Steam Turbine Simulation	#1
AliMobasher New Member Amini Join Date: Jun 2017 Posts: 3 Rep Power: 9	Dear all, I'm using Ansys CFX to simulate one stage of a steam turbine in a real operating condition. I'm using H2Olg as a homogeneous fluid and equilibrium simulation is considered. In inlet boundary when I use H2Og as "equilibrium constraint" and H2Ol as "equilibrium Fraction" everything is ok, but when I switch these options, the solver divergs with the error of "Maximum Mach Number". What's Wrong? Is it important to choose H2Og or H2Ol as "equilibrium Fraction"??? If "yes" which of H2Ol or H2Og should be selected as "equilibrium fraction"???

November 22, 2020, 12:02		#2
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,887 Rep Power: 27	It depends. In general, I would solve the fraction with most of the volume, and constraint with least volume, which is mostly the liquid. But if, by, far most of the mass is present in the liquid, then I could turn it around. It would be interesting to know how the mass on the inlet is distributed. Last edited by Gert-Jan; November 23, 2020 at 02:56.

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November 29, 2020, 12:23		#3
AliMobasher New Member Amini Join Date: Jun 2017 Posts: 3 Rep Power: 9	Thanks Gert-Jan for your reply. Yes it's rational to choose the dominant volume as constraint but in my case I have convergence problem with this choice. It's interesting to mention that I have a case solved with two options and the results are exactly same. but in another case I receive "Mach number error" with vapor phase as "fraction". It's more interesting to know that in this case the flow is certainly superheat and no liquid phase presents.