Compressible flow problem

bharath · March 5, 2014, 00:40

Hi to all,
I am simulating a compressible flow with Steam(Equilibirium) in CFX.My input BC's are,

Inlet Total Pressure = 0.05768 atm & T = 308.82 K (mass flow =111.17 kg/s)
Outlet Static Pressure = 0.05004 atm
Reference Pressure = 0 atm

Material: Steam Vapour (IAPWS table).

I started with water ideal gas and it is converged.When switching to steam it is not able start the calculation.
I tried different options and getting different warnings(Invalid number,Floating point, Over flow,High mach number,Table Clipping error and etc..)

Could anybody help me to solve this problem.

Thanks in Advance

ghorrocks · March 5, 2014, 05:24

IAPWS are always hard to converge.

You are using the ideal gas result as an initial condition? That will help a lot.

Also (the standard stuff for numerical instability): Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).

bharath · March 11, 2014, 06:03

Thanks Glenn for your reply.

1) After so many trials i managed to converge 2 cases (Total 5 different Pressure BC cases & Same mesh).But other cases reporting high Mach number and solver is failing.

2) How i can deal this high mach number warning...

ghorrocks · March 11, 2014, 07:21

As I said: Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).

March 5, 2014, 00:40	Compressible flow problem	#1
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	Hi to all, I am simulating a compressible flow with Steam(Equilibirium) in CFX.My input BC's are, Inlet Total Pressure = 0.05768 atm & T = 308.82 K (mass flow =111.17 kg/s) Outlet Static Pressure = 0.05004 atm Reference Pressure = 0 atm Material: Steam Vapour (IAPWS table). I started with water ideal gas and it is converged.When switching to steam it is not able start the calculation. I tried different options and getting different warnings(Invalid number,Floating point, Over flow,High mach number,Table Clipping error and etc..) Could anybody help me to solve this problem. Thanks in Advance

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March 5, 2014, 05:24		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	IAPWS are always hard to converge. You are using the ideal gas result as an initial condition? That will help a lot. Also (the standard stuff for numerical instability): Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).

March 11, 2014, 06:03		#3
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	Thanks Glenn for your reply. 1) After so many trials i managed to converge 2 cases (Total 5 different Pressure BC cases & Same mesh).But other cases reporting high Mach number and solver is failing. 2) How i can deal this high mach number warning...

March 11, 2014, 07:21		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	As I said: Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).